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© Nilam Publication Sdn. Bhd. 96
MODULE • Chemistry FORM 4
5UNIT
•	 Conductor and Electrolyte / Konduktor dan Elektrolit
–...
MODULE • Chemistry FORM 4
97 © Nilam Publication Sdn. Bhd.
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Electrolysis / Elektrolisis
1	 Substances can be classifi...
MODULE • Chemistry FORM 4
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	 Example of electrolytic cell / Contoh sel elektrolisis:...
MODULE • Chemistry FORM 4
99 © Nilam Publication Sdn. Bhd.
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Formation of Free Moving Ions in the Electrolyte
Pembentu...
MODULE • Chemistry FORM 4
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3	 Common half equation at the anode (anion/metal atom r...
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Set-up of apparatus / Rajah susunan radas:
Carbon electr...
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(b)	 Choose the ion to be discharged from the following ...
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(d)	 Complete the following table for the electrolysis o...
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	 (b)	 State the selected ions to be discharged at the a...
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The concentration of hydrochloric
acid after a while and...
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(b)	 Complete the following table for the electrolysis o...
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1	 Complete the table below / Lengkapkan jadual di bawah...
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	 Explanation / Penerangan:
–	 Potassium chloride soluti...
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Observation and half equation / Pemerhatian dan persamaa...
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Electrolysis in Industry / Elektrolisis dalam Industri
1...
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(a)	 State the name of the substance used as: / Nyatakan...
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6	 To electroplate an object with metal / Untuk menyadur...
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Magnesium
Magnesium
Copper(II) sulphate solution
Larutan...
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Electrical current produced is detected by the galvanome...
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7	 Daniell cell / Sel Daniell
(a)	 It is an example of v...
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8	 Four main uses of the Electrochemical Series:
	Empat ...
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2	 The diagram below shows the set-up of the apparatus t...
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	 Complete the following table to compare cell X and cel...
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(d)	 Referring to Cell A.
	 Merujuk kepada Sel A.
(i)	 W...
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1	 Which of the following is an electrolyte?
	 Antara be...
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6	 The diagram below shows the set-up of apparatus of a
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Unit 5 elektrokimia

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Unit 5 elektrokimia

  1. 1. © Nilam Publication Sdn. Bhd. 96 MODULE • Chemistry FORM 4 5UNIT • Conductor and Electrolyte / Konduktor dan Elektrolit – To differentiate between electrolyte and conductor with regard to electrical conductivity and any chemical changes that may occur. / Membezakan elektrolit dan konduktor dari segi kebolehan mengkonduksikan elektrik dan sebarang perubahan kimia yang berlaku. – To list examples of substances which are classified as electrolytes and conductors. Menyenaraikan contoh-contoh bahan yang dikelaskan sebagai elektrolit dan konduktor. • Electrolytic Cell / Sel Elektrolisis – To draw and label the electrolytic cell. / Melukis dan melabelkan sel elektrolisis. – To identify anode and cathode in the electrolytic cell diagram. / Mengenali anod dan katod dalam rajah sel elektrolisis. • Ionic Theory / Teori Ion – To relate the existence of free moving ions in an electrolyte with the electron flow in an external circuit. Mengaitkan kewujudan ion-ion yang bebas bergerak dalam elektrolit dengan proses pengaliran elektron dalam litar luar. – To explain the electrolysis process. / Menerangkan proses elektrolisis. – To conclude that electrolysis process involve changes from electrical energy to chemical energy. Membuat kesimpulan proses elektrolisis sebagai perubahan tenaga elektrik kepada tenaga kimia. • Formation of Free Moving Ions / Pembentukan Ion Bebas Bergerak – To differentiate molten and aqueous electrolytes. / Membezakan elektrolit leburan dan akueus. – To write the ionisation equation of molten and aqueous electrolytes. Menulis persamaan pengionan untuk elektrolit leburan dan akueus. • Reaction at Electrode / Tindak Balas di Elektrod – To write the discharge equation at the anode, where the anion releases electron. Focus on ions that are normally selected for discharge, such as chloride, hydroxide and bromide ions. Menulis persamaan di anod yang melibatkan anion melepaskan elektron. Fokus adalah kepada ion-ion yang biasa terpilih untuk nyahcas seperti ion klorida, ion hidroksida dan ion bromida. – To write the discharge equation at the cathode, where the cation receives electron. Focus on ions that are normally selected for discharge, such as hydrogen, copper(II) and silver ions. Menulis persamaan di katod yang melibatkan kation menerima elektron. Fokus adalah kepada ion yang biasa terpilih untuk nyahcas seperti ion hidrogen, ion kuprum(II) dan ion argentum. • Factors that Affect Reactions at the Electrodes / Faktor-Faktor yang Mempengaruhi Tindak Balas di Elektrod (i) The position of ions in the Electrochemical Series – for dilute solutions and inert electrodes. / Kedudukan ion dalam Siri Elektrokimia – bagi larutan cair dan elektrod lengai. (ii) The concentration – for concentrated solutions and inert electrodes / Kepekatan – bagi larutan pekat dan elektrod lengai (iii) The types of electrode – for diluted solutions and reactive electrodes / Jenis elektrod – bagi larutan cair dan elektrod tak lengai • Electrolysis in Industry / Kegunaan Elektrolisis dalam Industri – Electrolysis in electroplating, purifying and extracting metals / Elektrolisis dalam penyaduran, penulenan dan pengekstrakan logam ELECTROLYSIS / ELEKTROLISIS • Electrochemical Series / Siri Elektrokimia – To define and memorise the sequence of metal including hydrogen in the Electrochemical Series. Menakrif dan menghafal siri logam termasuk hidrogen dalam Siri Elektrokimia. • Application of Electrochemical Series in Displacement of Metals / Aplikasi Siri Elektrokimia dalam Penyesaran Logam – To predict the displacement of metal reactions based on the positions of metals in the Electrochemical Series. Meramal tindak balas penyesaran logam berdasarkan kedudukan logam dalam Siri Elektrokimia. – To write the equation of displacement reaction and to state the observations. Menulis persamaan tindak balas penyesaran dan menyatakan pemerhatian. – To describe the metal displacement experiment to construct the Electrochemical Series. Menghuraikan eksperimen penyesaran logam bagi membina Siri Elektrokimia. • Application of Electrochemical Series in Voltaic Cell / Aplikasi Siri Elektrokimia dalam Sel Kimia – To determine the negative and positive terminals of a voltaic cell. Menentukan terminal negatif dan positif suatu sel kimia. – To predict the voltage of voltaic cell. / Meramal voltan sel kimia. – To determine the direction of electron flow. / Menentukan arah pengaliran elektron. VOLTAIC CELL / SEL KIMIA 5 ELECTROCHEMISTRY ELEKTROKIMIA 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 96 9/18/15 5:05 PM
  2. 2. MODULE • Chemistry FORM 4 97 © Nilam Publication Sdn. Bhd. 5UNIT Electrolysis / Elektrolisis 1 Substances can be classified into three types based on electrical conductivity. Bahan boleh dibahagikan kepada tiga jenis berdasarkan kekonduksian elektrik. Type of substance Jenis bahan Definition Definisi Example Contoh Conductor Konduktor Element that can conduct electricity in solid or molten state without any chemical changes , normally metals and carbon. Unsur yang boleh mengkonduksi arus elektrik dalam keadaan pepejal atau leburan tanpa perubahan kimia , biasanya logam dan karbon. Copper, lead, tin, silver and carbon Kuprum, plumbum, stanum, argentum dan karbon Electrolyte Elektrolit Compounds that can conduct electricity in *molten state or *aqueous solution and undergo chemical changes . Sebatian yang boleh mengkonduksikan arus elektrik dalam keadaan *lebur atau *akueus serta mengalami perubahan kimia . * Molten state: a solid that is heated until it melts. * Lebur: pepejal yang dipanaskan sehingga cair. * Aqueous solution: a solid that is dissolved in water. * Akueus: pepejal yang larut di dalam air. – Aqueous solution of ionic compound such as copper(II) sulphate solution and sodium chloride solution. Larutan akueus bagi sebatian ion contohnya larutan kuprum(II) sulfat dan larutan natrium klorida. – Aqueous solution of *acid or alkali such as hydrochloric acid (HCl) and ammonia solution (NH3 ). Larutan akueus *asid atau alkali contohnya asid hidroklorik (HCl) dan larutan ammonia (NH3). – Molten ionic compounds such as molten lead(II) bromide, molten sodium chloride and molten aluminium oxide. Leburan sebatian ion contohnya leburan plumbum(II) bromida, leburan natrium klorida dan leburan aluminium oksida. * HCl and NH3 are covalent compounds, exist in the form of molecule without water but ionised in water. (Explanation is in the next topic i.e acid and base) * HCl dan NH3 adalah sebatian kovalen, yang terdiri daripada molekul dalam keadaan tanpa air tetapi ianya terion dalam air (akan dijelaskan dalam tajuk seterusnya iaitu dalam asid dan bes) Non-electrolyte Bukan elektrolit Compounds that cannot conduct electricity in solid, molten and aqueous solution. Sebatian kimia yang tidak boleh mengkonduksikan elektrik dalam keadaan pepejal, lebur dan akueus. Molten covalent compound such as naphthalene, molten sulphur and liquid bromine. Leburan sebatian kovalen contohnya naftalena, sulfur lebur dan cecair bromin. 2 Electrolysis is a process whereby an electrolyte is decomposed to its constituent elements when electric current passes through it. Elektrolisis adalah proses penguraian elektrolit kepada unsur juzuknya apabila arus elektrik dialirkan melaluinya. 3 Energy change in electrolysis process is electric energy to chemical energy . Perubahan tenaga dalam proses elektrolisis adalah dari tenaga elektrik kepada tenaga kimia . 4 Conductor which is dipped into electrolyte which carries electric current in and out of electrolyte is called an electrode . Electrode is normally made up of inert substance such as carbon. Konduktor yang dicelup dalam elektrolit yang mengalirkan arus elektrik ke dalam dan keluar daripada elektrolit dipanggil elektrod . Elektrod biasanya terdiri daripada bahan lengai seperti karbon. 5 An electrolytic cell is a set-up of apparatus that contains two electrodes which are dipped in an electrolyte and produce a chemical reaction when connected to a battery (source of electricity). Sel elektrolisis adalah susunan radas yang terdiri daripada dua elektrod yang dicelup ke dalam elektrolit dan menghasilkan tindak balas kimia apabila disambungkan kepada bateri (sumber arus elektrik). 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 97 9/18/15 5:05 PM
  3. 3. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 98 5UNIT Example of electrolytic cell / Contoh sel elektrolisis: (i) (ii) (iii) 6 Electric current from the battery flows into the electrolyte through the electrode. There are two types of electrode in the electrolytic cell: Arus elektrik dari bateri mengalir ke dalam elektrolit melalui elektrod. Terdapat dua jenis elektrod dalam sel elektrolisis: (a) Anode: An electrode that is connected to the positive terminal of the battery. Anod: Elektrod yang disambung kepada terminal positif bateri dalam sel elektrolisis. (b) Cathode: An electrode that is connected to the negative terminal of the battery. Katod: Elektrod yang disambung kepada terminal negatif bateri dalam sel elektrolisis. 7 An electrolyte consists of free moving ions because it is in a molten or aqueous state. Each ion moves to the opposite charge electrode. There are two types of ions in electrolyte: Dalam keadaan lebur atau akueus, elektrolit terdiri daripada ion-ion yang bergerak bebas. Setiap ion bergerak kepada elektrod yang bertentangan cas. Terdapat dua jenis ion dalam elektrolit: (a) Anions: Negative ions which are attracted and move to the positively charged electrode, anode . Anion: Ion negatif akan tertarik dan bergerak ke arah elektrod anod yang bercas positif . (b) Cations: Positive ions which are attracted and move to the negatively charged electrode, cathode . Kation: Ion positif akan tertarik dan bergerak ke arah elektrod katod yang bercas negatif . 8 Electrolysis occurs at the electrode when electric current flows in the electrolytic cell. The stages in electrolysis process are: Proses elektrolisis berlaku di elektrod apabila arus elektrik mengalir melalui sel elektrolisis. Peringkat dalam proses elektrolisis adalah seperti berikut: (a) Anions (negative ions) are attracted and move to the anode . The anions release electrons to the surface of anode and become neutral atoms or molecule. The anions are discharged at the anode. Anion (ion negatif) akan tertarik dan bergerak ke arah anod . Anion melepaskan elektron pada permukaan anod dan menjadi atom/molekul. Anion dinyahcaskan pada anod. (b) Electrons flow from the anode to the cathode through the connecting wire in the external circuit . Elektron mengalir dari anod ke katod melalui wayar penyambung dalam litar luar . (c) Cations (positive ions) are attracted and move to the cathode . The cations receive electrons at the surface of cathode and become neutral atoms or molecules. The cations are discharged at the cathode. Kation (ion positif) akan tertarik dan bergerak ke arah katod . Kation menerima elektron pada permukaan katod dan menjadi atom/molekul. Kation dinyahcaskan pada katod. – Electrons flow through the external circuit. Elektron mengalir melalui litar luar. – Chemical changes occur at the anode and cathode. Perubahan kimia berlaku di anod dan katod. Heat Panaskan A A Electrodes Elektrod Electrodes Elektrod Electrolyte Elektrolit Electrolyte Elektrolit Electrolyte Elektrolit Electrode Elektrod Electrode Elektrod Electrolysis of aqueous electrolyte (Gas is released) Elektrolisis elektrolit dalam bentuk akueus (Gas dibebaskan) Electrolysis of aqueous electrolyte (No gas released) Elektrolisis elektrolit dalam bentuk akueus (Tiada gas dibebaskan)Electrolysis of molten electrolyte Elektrolisis elektrolit lebur 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 98 9/18/15 5:05 PM
  4. 4. MODULE • Chemistry FORM 4 99 © Nilam Publication Sdn. Bhd. 5UNIT Formation of Free Moving Ions in the Electrolyte Pembentukan Ion Bergerak Bebas dalam Elektrolit 1 Ionisation equation is an equation to determine the ions present in molten or aqueous electrolyte. Persamaan pengionan adalah persamaan yang menunjukkan ion yang hadir dalam elektrolit sama ada dalam keadaan leburan atau akueus. (a) Example of ionisation of molten electrolyte (a compound that is heated until it melts) Contoh pengionan elektrolit dalam keadaan leburan (sebatian yang dipanaskan sehingga lebur) (i) Molten sodium chloride / Natrium klorida lebur : NaCl (s/p) Na+ (l/ce) + Cl– (l/ce) (ii) Molten lead(II) bromide / Plumbum(II) bromida lebur: PbBr2 (s/p) Pb2+ (l/ce) + 2Br– (l/ce) (iii) Molten sodium oxide / Natrium oksida lebur: Na2O (s/p) 2Na+ (l/ce) + O2– (l/ce) (iv) Molten aluminium oxide / Aluminium oksida lebur: Al2O3 (s/p) 2Al3+ (l/ce) + 3O2– (l/ce) (b) Example of the ionisation of an aqueous electrolyte (a compound that is dissolved in water): Contoh pengionan elektrolit dalam keadaan akueus (sebatian yang dilarutkan dalam air): (i) Sodium chloride solution / Larutan natrium klorida: NaCl(aq/ak) Na+ (aq/ak) + Cl– (aq/ak) H2O H+ (aq/ak) + OH– (aq/ak) (ii) Copper(II) sulphate solution / Larutan kuprum(II) sulfat: CuSO4(aq/ak) Cu2+ + SO4 2– H2O H+ + OH– (iii) Sulphuric acid / Asid sulfurik: H2SO4(aq/ak) 2H+ + SO4 2– H2O H+ + OH– 2 Ionisation of molten electrolyte produces cation and anion of the compound only. However the ionisation of an aqueous electrolyte produces cation and anion from the ionisation of the compound and water. Pengionan elektrolit dalam keadaan lebur hanya menghasilkan kation dan anion dari sebatian itu sahaja. Pengionan elektrolit dalam keadaan akueus menghasilkan kation dan anion daripada sebatian dan air. Example / Contoh: (i) Ionisation of molten sodium chloride produces Na+ and Cl– only. Pengionan natrium klorida leburan menghasilkan Na+ dan Cl– sahaja. (ii) Ionisation of aqueous sodium chloride produces Na+ , H+ , Cl– and OH– . Pengionan larutan akueus natrium klorida menghasilkan Na+ , H+ , Cl– dan OH– . Reactions at the Electrodes / Tindak Balas di Elektrod 1 The process of cation gaining electrons at the cathode or anion losing electrons at the anode is called discharged : Proses apabila kation menerima elektron di katod atau anion melepaskan elektron di anod dipanggil nyahcas : (a) A cation is discharged when it receives electrons at the cathode. Kation dinyahcaskan apabila menerima elektron di katod. (b) An anion is discharged when it releases electrons at the anode. Anion dinyahcaskan apabila melepaskan elektron di anod. (c) When ions are discharged , they become neutral atoms or molecules . Apabila ion dinyahcaskan , ianya akan menjadi atom atau molekul yang neutral. 2 The ionic equation that occurs at the anode and cathode to produce neutral atom or molecule is called ‘half equation’. Persamaan ion yang berlaku di anod dan di katod untuk menghasilkan atom atau molekul neutral dipanggil ‘persamaan setengah’. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 99 9/18/15 5:05 PM
  5. 5. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 100 5UNIT 3 Common half equation at the anode (anion/metal atom releases electrons): Persamaan setengah yang biasa di anod (anion/atom logam melepaskan elektron): Half equation Persamaan setengah Explanation Penerangan 4OH– 2H2O + O2 + 4e Four hydroxide ions release four electrons to form two water molecules and one oxygen molecule . Empat ion hidroksida melepaskan empat elektron membentuk dua molekul air dan satu molekul oksigen. 2Cl– Cl2 + 2e Two chloride ions release two electrons to form one chlorine molecule . Dua ion klorida melepaskan dua elektron membentuk satu molekul klorin. 2Br– Br2 + 2e Two bromide ions release two electrons to form one bromine molecule . Dua ion bromida melepaskan dua elektron membentuk satu molekul bromin. Cu Cu2+ + 2e Copper atom releases two electrons to form copper(II) ion . Atom kuprum melepaskan dua elektron membentuk ion kuprum(II) . Ag Ag+ + e Silver atom releases one electron to form silver ion . Atom argentum melepaskan satu elektron membentuk ion argentum . 4 Common half equation at the cathode (cation receives electrons): Persamaan setengah yang biasa di katod (kation menerima elektron): Half equation Persamaan setengah Explanation Penerangan 2H+ + 2e H2 Two hydrogen ions receive two electrons to form one hydrogen molecule . Dua ion hidrogen menerima dua elektron membentuk satu molekul hidrogen. Ag+ + e Ag Silver ion receive one electron to form one silver atom . Ion argentum menerima satu elektron membentuk satu atom argentum. Cu2+ + 2e Cu Copper(II) ion receives two electrons to form one copper atom . Ion kuprum(II) menerima dua elektron membentuk satu atom kuprum. 5 Write the half equation of discharge of ion: Tuliskan persamaan setengah untuk nyahcas ion yang berikut: (i) Lead(II) ion to lead atom : Pb2+ + 2e Pb Ion plumbum(II) kepada atom plumbum (ii) Silver ion to silver atom : Ag+ + e Ag Ion argentum kepada atom argentum (iii) Iodide ion to iodine molecule : 2I– I2 + 2e Ion iodida kepada molekul iodin Using lead(II) bromide as an example, explain the electrolysis of molten lead(II) bromide. In your explanation, draw a labelled diagram for the set-up of apparatus and show the movement of particles by using arrows that occur in lead(II) bromide and the direction of electron flow in the external circuit. Dengan menggunakan plumbum(II) bromida sebagai contoh, jelaskan elektrolisis plumbum(II) bromida leburan. Dalam penerangan anda, lukiskan satu rajah susunan radas berlabel dan tunjukkan dengan anak panah pergerakan zarah yang berlaku dalam plumbum(II) bromida serta arah aliran elektron dalam litar luar. Exercise / Latihan 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 100 9/18/15 5:05 PM
  6. 6. MODULE • Chemistry FORM 4 101 © Nilam Publication Sdn. Bhd. 5UNIT Set-up of apparatus / Rajah susunan radas: Carbon electrodes Elektrod karbon Lead(II) bromide Plumbum(II) bromida Heat Panaskan Explanation / Penerangan: The ions present are lead(II) ions/ Pb2+ and bromide ions/ Br– . Bromide ion/ Br– move to the anode. Bromide ion/ Br– releases one electron to form bromine atom at the anode. Two bromine atoms combine to form bromine molecule. 2Br– Br2 + 2e. Lead(II) ions/Pb2+ move to the cathode. Lead(II) ions/Pb2+ receive two electrons to form lead atom at the cathode. Pb2+ + 2e Pb. Ion yang hadir adalah ion plumbum(II) /Pb2+ dan ion bromida/Br– . Ion Bromida/Br– bergerak ke arah anod. Ion Bromida/Br– membebaskan satu elektron untuk membentuk atom bromin di anod. Dua atom bromin bergabung dan membentuk molekul bromin. 2Br– Br2 + 2e. Ion plumbum(II)/Pb2+ bergerak ke arah katod. Ion plumbum(II)/Pb2+ menerima dua elektron untuk membentuk atom plumbum di katod. Pb2+ + 2e Pb. Factors that Affect the Electrolysis of an Aqueous Solution Faktor-faktor yang Mempengaruhi Elektrolisis Larutan Akueus 1 When more than one type of ion are attracted towards the electrodes during electrolysis, only one type of ion is selected to be discharged at each electrode. Selective discharge only occurs in aqueous solution because it usually has more than one type of ion attracted to the anode or cathode. Apabila lebih dari satu jenis ion bergerak ke elektrod semasa elektrolisis, hanya satu jenis ion sahaja yang akan dipilih untuk dinyahcas pada setiap elektrod. Pemilihan nyahcas ion hanya berlaku di dalam larutan akueus sahaja kerana ia biasanya mempunyai lebih dari satu jenis ion yang tertarik ke anod atau katod. 2 The selection of ion for discharge depends on three factors: Pemilihan ion untuk nyahcas bergantung pada tiga faktor: (a) The position of ions in the Electrochemical Series (normally in dilute solution and inert electrode). Kedudukan ion dalam Siri Elektrokimia (biasanya dalam larutan cair dan elektrod lengai). (b) The concentration of electrolyte (normally in concentrated solution and inert electrode). Kepekatan elektrolit (biasanya dalam larutan pekat dan elektrod lengai). (c) The types of electrode (when metal as electrode is used). Jenis elektrod (apabila elektrod logam digunakan). 3 The position of ions in the Electrochemical Series: Kedudukan ion dalam Siri Elektrokimia: (a) When electrolysis is conducted on dilute solution and inert electrodes, the cation at the lower position in the Electrochemical Series, or anions in the lower position of the anion discharge series will be selected to be discharged. Apabila elektrolisis dijalankan ke atas larutan cair dan elektrod lengai, kation yang lebih rendah kedudukan dalam Siri Elektrokimia atau anion yang lebih rendah kedudukan dalam siri discas anion akan dinyahcas. Cation: K+ , Na+ , Ca2+ , Mg2+ , Al3+ , Zn2+ , Fe2+ , Sn2+ , Pb2+ , H+ , Cu2+ , Ag+ , and Au+ Kation: K+ , Na+ , Ca2+ , Mg2+ , Al3+ , Zn2+ , Fe2+ , Sn2+ , Pb2+ , H+ , Cu2+ , Ag+ , dan Au+ Increasing ease of discharge of ion from left to right Ion semakin mudah dinyahcas dari kiri ke kanan Anion: F– , SO4 2– , NO3 – , Cl– , Br– , I– , and OH– Anion: F– , SO4 2– , NO3 – , Cl– , Br– , I– , dan OH– 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 101 9/18/15 5:05 PM
  7. 7. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 102 5UNIT (b) Choose the ion to be discharged from the following pairs of ions. State the electrode where it occurs and write the half equation for the discharge of ion: Pilih ion yang akan dinyahcas dari pasangan ion berikut, nyatakan di elektrod mana ia berlaku dan tulis persamaan setengah untuk nyahcas ion: (i) Hydroxide sulphate ions : Half equation: 4OH– 2H2O + O2 + 4e at the anode . Ion hidroksida ion sulfat : Persamaan setengah: 4OH– 2H2O + O2 + 4e di anod . (ii) Hydroxide nitrate ions : Half equation: 4OH– 2H2O + O2 + 4e at the anode . Ion hidroksida ion nitrat : Persamaan setengah: 4OH– 2H2O + O2 + 4e di anod . (iii) Hydrogen copper(II) ions : Half equation: Cu2+ + 2e Cu at the cathode . Ion hidrogen ion kuprum(II) : Persamaan setengah: Cu2+ + 2e Cu di katod . (iv) Hydrogen potassium ions : Half equation: 2H+ + 2e H2 at the cathode . Ion hidrogen ion kalium : Persamaan setengah: 2H+ + 2e H2 di katod . (v) Hydrogen silver ions : Half equation: Ag+ + e Ag at the cathode . Ion hidrogen ion argentum : Persamaan setengah: Ag+ + e Ag di katod . (c) Complete the following table for the electrolysis of 0.1 mol dm–3 sodium nitrate solution using carbon electrode. Lengkapkan jadual berikut bagi elektrolisis larutan natrium nitrat 0.1 mol dm–3 menggunakan elektrod karbon. Set-up of apparatus Susunan radas Carbon electrodes Elektrod karbon Sodium nitrate solution Larutan natrium nitrat Equation of electrolyte ionisation Persamaan pengionan elektrolit NaNO3 Na+ + NO3 – H2O H+ + OH– Electrode / Elektrod Anode / Anod Cathode / Katod Ions that are attracted to the anode and cathode Ion yang ditarik ke anod dan katod NO3 – , OH– Na+ , H+ Half equation Persamaan setengah 4OH– 2H2O + O2 + 4e 2H+ + 2e H2 Name of the products Nama hasil Oxygen Oksigen Hydrogen Hidrogen Observations Pemerhatian Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Confirmatory test (method and observations) Ujian pengesahan (kaedah dan pemerhatian) – Insert a glowing wooden splinter into test tube. Masukkan kayu uji berbara ke dalam tabung uji. – Glowing wooden splinter is lighted up. Kayu uji berbara menyala. – When a lighted wooden splinter is placed near the mouth of the test tube – Apabila kayu uji menyala diletakkan di mulut ujian tabung uji – A ‘pop’ sound is produced. Bunyi ‘pop’ dihasilkan. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 102 9/18/15 5:05 PM
  8. 8. MODULE • Chemistry FORM 4 103 © Nilam Publication Sdn. Bhd. 5UNIT (d) Complete the following table for the electrolysis of 0.1 mol dm–3 sulphuric acid using carbon electrodes. Lengkapkan jadual berikut bagi elektrolisis asid sulfurik 0.1 mol dm–3 menggunakan elektrod karbon. Set-up of apparatus Susunan radas Carbon electrodes Elektrod karbon Sulphuric acid Asid sulfurik Equation of electrolyte ionisation Persamaan pengionan elektrolit H2SO4 2H+ + SO4 2– H2O H+ + OH– Electrode / Elektrod Anode / Anod Cathode / Katod Ions that are attracted to the anode and cathode Ion yang ditarik ke anod dan katod SO4 2– , OH– H+ Half equation Persamaan setengah 4OH– 2H2O + O2 + 4e 2H+ + 2e H2 Name of the products Nama hasil Oxygen Oksigen Hydrogen Hidrogen Observations Pemerhatian Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Confirmatory test (method and observations) Ujian pengesahan (kaedah dan pemerhatian) – Insert a glowing wooden splinter into test tube. Masukkan kayu uji berbara ke dalam tabung uji. – Glowing wooden splinter is lighted up. Kayu uji berbara menyala. – When a lighted wooden splinter is placed near the mouth of the test tube. Apabila kayu uji menyala diletakkan di mulut ujian tabung uji. – A ‘pop’ sound is produced. Bunyi ‘pop’ dihasilkan. (e) Complete the following table for the electrolysis of 0.1 mol dm–3 copper(II) sulphate solution using carbon electrodes. Lengkapkan jadual berikut bagi elektrolisis larutan kuprum(II) sulfat 0.1 mol dm–3 menggunakan elektrod karbon. Set-up of apparatus Susunan radas Carbon electrodes Elektrod karbon Copper(II) sulphate solution Larutan kuprum(II) sulfat Equation of electrolyte ionisation Persamaan pengionan elektrolit CuSO4 Cu2+ + SO4 2– H2O H+ + OH– Electrode / Elektrod Anode / Anod Cathode / Katod Ions that are attracted to the anode and cathode Ion yang ditarik ke anod dan katod SO4 2– , OH– Cu2+ , H+ Half equation Persamaan setengah 4OH– 2H2O + O2 + 4e Cu2+ + 2e Cu Name of the products Nama hasil Oxygen Oksigen Copper Kuprum Observations Pemerhatian Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Brown solid deposited. Pepejal perang terenap. Confirmatory test (method and observations) Ujian pengesahan (kaedah dan pemerhatian) – Insert a glowing wooden splinter into test tube. Masukkan kayu uji berbara ke dalam tabung uji. – Glowing wooden splinter is lighted up. Kayu uji berbara menyala – 4 Concentration of electrolyte / Kepekatan elektrolit: (a) When electrolysis is carried out using inert electrodes and concentrated solutions, ions that are more concentrated will be discharged but this is only true for halide ions, which are Cl– , Br– and I– . Apabila elektrolisis dijalankan menggunakan elektrod lengai dan larutan pekat, ion yang lebih pekat akan dinyahcas tetapi ia benar untuk ion-ion halida sahaja iaitu Cl– , Br– dan I– . 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 103 9/18/15 5:05 PM
  9. 9. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 104 5UNIT (b) State the selected ions to be discharged at the anode and cathode for the following concentrated solutions. Nyatakan ion yang terpilih untuk dinyahcaskan di anod dan di katod bagi larutan pekat di bawah. (i) Concentrated hydrochloric acid solution, using carbon electrodes Larutan asid hidroklorik pekat menggunakan elektrod karbon Anode / Anod : Cl– Cathode / Katod : H+ (ii) Concentrated potassium iodide solution, using carbon electrodes Larutan kalium iodida pekat menggunakan elektrod karbon Anode / Anod : l– Cathode / Katod : H+ (iii) Concentrated sodium chloride solution, using carbon electrodes Larutan natrium klorida pekat menggunakan elektrod karbon Anode / Anod : Cl– Cathode / Katod : H+ (c) Complete the following table for the electrolysis of 0.001 mol dm–3 hydrochloric acid and 2.0 mol dm–3 hydrochloric acid, using carbon electrodes. Lengkapkan jadual berikut bagi elektrolisis asid hidroklorik 0.001 mol dm–3 dan asid hidroklorik 2.0 mol dm–3 menggunakan elektrod karbon. Set-up of apparatus Susunan radas Hydrochloric acid Asid hidroklorik Carbon electrodes Elektrod karbon Equation of electrolyte ionisation Persamaan pengionan elektrolit HCl H+ + Cl– H2O H+ + OH– Electrolyte / Elektrolit 0.001 mol dm-3 of HCl / HCl 0.001 mol dm–3 2.0 mol dm-3 of HCl / HCl 2.0 mol dm–3 Ions that are attracted to the cathode Ion bergerak ke katod H+ H+ Half equation at the cathode Persamaan setengah di katod 2H+ + 2e H2 2H+ + 2e H2 Observation at cathode Pemerhatian di katod Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Confirmatory test at cathode (method and observations) Ujian pengesahan (kaedah dan pemerhatian) – Place a burning wooden splinter at the mouth of the test tube / Apabila kayu uji menyala diletakkan di mulut tabung uji – A ‘pop’ sound is produced. Bunyi ‘pop’ dihasilkan. – Place a burning wooden splinter at the mouth of the test tube / Apabila kayu uji menyala diletakkan di mulut tabung uji – A ‘pop’ sound is produced. Bunyi ‘pop’ dihasilkan. Name the product at the cathode Nama hasil di katod Hydrogen gas Gas hidrogen Hydrogen gas Gas hidrogen Ions that are attracted to the anode Ion bergerak ke anod Cl– , OH– Cl– , OH– Half equation at the anode Persamaan setengah di anod 4OH– 2H2O + O2 + 4e 2Cl– Cl2 + 2e Observations at anode Pemerhatian di anode Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Greenish yellow gas is released. Gas kuning kehijauan dibebaskan. Confirmatory test at anode (method and observations) Ujian pengesahan (kaedah dan pemerhatian) – Insert a glowing wooden splinter into the test tube. Masukkan kayu uji berbara ke dalam tabung uji. – Glowing wooden splinter is lighted up. Kayu uji berbara menyala. – A damp blue litmus paper is placed near the mouth of the test tube. / Sehelai kertas litmus biru lembap diletakkan di mulut tabung uji. – The gas changed the damp blue litmus paper to red and then bleached it. Gas ini menukarkan kertas litmus biru lembap kepada merah dan kemudian melunturkannya. Name the product at the anode Nama hasil di anod Oxygen gas Gas oksigen Chlorine gas Gas klorin 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 104 9/18/15 5:05 PM
  10. 10. MODULE • Chemistry FORM 4 105 © Nilam Publication Sdn. Bhd. 5UNIT The concentration of hydrochloric acid after a while and explanation Kepekatan elektrolit selepas beberapa ketika dan terangkan Concentration of hydrochloric acid increases . Hydrogen gas is released at the cathode and oxygen gas is released at the anode. Water decomposed to oxygen gas and hydrogen gas. Kepekatan asid hidroklorik bertambah . Gas hidrogen dibebaskan di katod dan gas oksigen dibebaskan di anod. Air terurai kepada gas oksigen dan gas hidrogen . Concentration of hydrochloric acid decreases . Hydrogen gas released at the cathode and chlorine gas released at the anode. Concentration of chloride ions decreases. Kepekatan asid hidroklorik berkurang . Gas hidrogen dibebaskan di katod dan gas klorin dibebaskan di anod. Kepekatan ion klorida berkurang. (d) Complete the following table for the electrolysis of 2.0 mol dm–3 sodium iodide solution using carbon electrodes. Lengkapkan jadual berikut bagi elektrolisis larutan natrium iodida 2.0 mol dm–3 menggunakan elektrod karbon. Set-up of apparatus Susunan radas Carbon electrodes Elektrod karbon Sodium iodide solution Larutan natrium iodida Equation of electrolyte ionisation Persamaan pengionan elektrolit NaI Na+ + I– H2O H+ + OH– Electrode / Elektrod Anode / Anod Cathode / Katod Ions that are attracted to the anode and cathode Ion yang ditarik ke anod dan katod I– , OH– Na+ , H+ Half equation Persamaan setengah 2I– I2 + 2e 2H+ + 2e H2 Name of the products Nama hasil Iodine Iodin Hydrogen Hidrogen Observations Pemerhatian Brown solution is formed. Larutan perang terbentuk. Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Confirmatory test (method and observations) Ujian pengesahan (kaedah dan pemerhatian) – A few drops of starch solution is added. Beberapa titik larutan kanji ditambah. – Starch solution turns dark blue. Larutan kanji menjadi biru gelap. – When a lighted wooden splinter is placed near the mouth of the test tube. Apabila kayu uji menyala diletakkan di mulut tabung uji. – A ‘pop’ sound is produced. Bunyi ‘pop’ dihasilkan. 5 Types of electrode: Jenis elektrod: (a) There are two types of electrode: Terdapat dua jenis elektrod: (i) Inert electrode – An electrode that acts as a conductor only and does not undergo any chemical changes. Normally they are made of carbon or platinum. Elektrod lengai – Elektrod yang bertindak sebagai pengalir arus sahaja dan tidak mengalami perubahan kimia. Biasanya diperbuat daripada karbon atau platinum. (ii) Reactive electrode – An electrode that does not only act as a conductor but also undergoes chemical changes. During the electrolysis, the metal atom at the anode releases electron to form metal ion, metal anode becomes thinner while the less electropositive cation will be selected at the cathode which is electrodes such as copper, silver and nickel. Elektrod reaktif – Elektrod yang bertindak bukan sahaja sebagai pengalir arus tetapi juga mengalami perubahan kimia. Semasa proses elektrolisis berlaku, atom logam pada anod melepaskan elektron menjadi ion logam, anod logam menjadi nipis manakala ion yang kurang elektropositif akan menyahcas di katod yang terdiri daripada logam seperti kuprum, argentum dan nikel. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 105 9/18/15 5:05 PM
  11. 11. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 106 5UNIT (b) Complete the following table for the electrolysis of 1 mol dm–3 copper(II) sulphate solution with carbon electrode and copper electrode. Lengkapkan jadual berikut bagi elektrolisis larutan kuprum(II) sulfat 1 mol dm–3 menggunakan elektrod karbon dan elektrod kuprum. Set-up of apparatus Susunan radas Copper(II) sulphate solution Larutan kuprum(II) sulfat Carbon electrodes Elektrod karbon Copper electrodes Elektrod kuprum Copper(II) sulphate solution Larutan kuprum(II) sulfat Equation of electrolyte ionisation Persamaan pengionan elektrolit CuSO4 (aq/ak) Cu2+ + SO4 2– H2O H+ + OH– Type of electrode Jenis elektrod Carbon electrode Elektrod karbon Copper electrode Elektrod kuprum The ions that move to the cathode Ion bergerak ke katod Cu2+ , H+ Cu2+ , H+ Half equation at the cathode Persamaan setengah di katod Cu2+ + 2e Cu Cu2+ + 2e Cu Name the product at the cathode Nama hasil di katod Copper Kuprum Copper Kuprum Observation at cathode Pemerhatian di katod Brown solid deposited Enapan perang terbentuk Brown solid deposited Enapan perang terbentuk The ions that move to the anode Ion bergerak ke anod SO4 2– , OH– SO4 2– , OH– Half equation at the anode Persamaan setengah di anod 4OH– 2H2O + O2 + 4e Cu Cu2+ + 2e Name the product at anode Nama hasil di anod Oxygen gas Gas oksigen Copper(II) ion Ion kuprum(II) Observations at the anode Pemerhatian di anod – Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. – Intensity of blue colour solution decreases. Keamatan warna larutan biru berkurang. – Copper electrode becomes thinner. Elektrod kuprum semakis nipis. – Intensity of blue colour solution remains unchanged. Keamatan warna larutan biru tidak berubah. Confirmatory test (method and observations) Ujian pengesahan (kaedah dan pemerhatian) – Insert a glowing wooden splinter into the test tube. Masukkan kayu uji berbara ke dalam tabung uji. – Glowing wooden splinter is lighted up. Kayu uji berbara menyala. – The concentration of copper(II) solution after a while and explanation Kepekatan elektrolit selepas beberapa ketika dan terangkan – Concentration of copper(II) sulphate solution decreases. Kepekatan larutan kuprum(II) sulfat berkurang. – Copper(II) ions is discharged to become copper atoms and deposited at the cathode. Ion kuprum(II) dinyahcas menjadi atom kuprum dan terenap di katod. – Concentration of copper(II) sulphate solution remains unchanged. Kepekatan larutan kuprum(II) sulfat tidak berubah. – The number of copper atoms form at the anode is equal to the number of copper(II) ions form at the cathode. Bilangan atom kuprum yang menjadi ion kuprum(II) di anod adalah sama dengan bilangan ion kuprum(II) yang menjadi atom kuprum dan terenap di katod. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 106 9/18/15 5:05 PM
  12. 12. MODULE • Chemistry FORM 4 107 © Nilam Publication Sdn. Bhd. 5UNIT 1 Complete the table below / Lengkapkan jadual di bawah: Electrolyte Elektrolit Electrode Elektrod Factor that affects electrolysis Faktor yang mempengaruhi elektrolisis Ions present Ion yang hadir Half equation at the anode and observation Persamaan setengah di anod dan pemerhatian Half equation at the cathode and observation Persamaan setengah di katod dan pemerhatian Dilute sulphuric acid Asid sulfurik cair Carbon Karbon Position of ion in the Electrochemical Series Kedudukan ion dalam Siri Elektrokimia H+ , SO4 2– , OH– 4OH– 2H2O + O2 + 4e Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. 2H+ + 2e H2 Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Concentrated hydrochloric acid Asid hidroklorik pekat Carbon Karbon Concentration of electrolyte Kepekatan elektrolit H+ , Cl– , OH– 2Cl– Cl2 + 2e Greenish yellow gas is released. Gas kuning kehijauan dibebaskan. 2H+ + 2e H2 Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Silver nitrate solution Larutan argentum nitrat Carbon Karbon Position of ion in the Electrochemical Series Kedudukan ion dalam Siri Elektrokimia Ag+ , NO3 – , H+ , OH– 4OH– 2H2O + O2 + 4e Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Ag+ + e Ag Grey shiny solid deposited. Pepejal kelabu berkilat terenap. Silver nitrate solution Larutan argentum nitrat Silver Argentum Type of electrode Jenis elektrod Ag+ , NO3 – , H+ , OH– Ag Ag+ + e Anode becomes thinner. Anod menjadi semakin nipis. Ag+ + e Ag Grey shiny solid deposited. Pepejal kelabu berkilat terenap Dilute potassium iodide solution Larutan kalium iodida cair Carbon Karbon Position of ion in the Electrochemical Series Kedudukan ion dalam Siri Elektrokimia K+ , I– , H+ , OH– 4OH– 2H2O + O2 + 4e Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. 2H+ + 2e H2 Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Concentrated potassium iodide solution Larutan kalium iodida pekat Carbon Karbon Concentration of electrolyte Kepekatan elektrolit K+ , I– , H+ , OH– 2I– I2 + 2e Brown solution formed. Larutan perang terhasil. 2H+ + 2e H2 Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. Dilute potassium sulphate solution Larutan kalium sulfat cair Carbon Karbon Position of ion in the Electrochemical Series Kedudukan ion dalam Siri Elektrokimia K+ , SO4 2– , H+ , OH– 4OH– 2H2O + O2 +4e Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. 2H+ + 2e H2 Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. 2 Electrolysis is carried out on dilute potassium chloride solution using carbon electrodes. Explain how this electrolysis occurs. Use a labelled diagram to explain your answer. Proses elektrolisis dijalankan ke atas larutan kalium klorida cair menggunakan elektrod karbon. Jelaskan bagaimana proses elektrolisis ini berlaku. Gunakan gambar rajah berlabel untuk menerangkan jawapan anda. Set-up of apparatus / Susunan radas: Carbon electrode Elektrod karbon Carbon electrode Elektrod karbon Dilute potassium chloride solution Larutan kalium klorida Exercise / Latihan 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 107 9/18/15 5:05 PM
  13. 13. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 108 5UNIT Explanation / Penerangan: – Potassium chloride solution consists of K+ , H+ , Cl– and OH– ions that move freely. Larutan kalium klorida mengandungi ion K+ , H+ , Cl– dan OH– yang bergerak bebas. – Cl– ion and OH– ion move to the anode. Ion Cl– dan ion OH– bergerak ke anod. – OH– ion is lower than Cl– ion in the Electrochemical Series. Ion OH– terletak di bawah ion Cl– dalam Siri Elektrokimia. – OH– ion is selectively discharged by releasing electrons to form oxygen and water molecules. Ion OH– dipilih untuk dinyahcaskan dengan melepaskan elektron membentuk molekul oksigen dan air . – Half equation / Persamaan setengah: 4OH– 2H2O + O2 + 4e . – H+ ion is lower than K+ ion in the Electrochemical Series. Ion H+ terletak di bawah ion K+ dalam Siri Elektrokimia. – H+ ion is selectively discharged by receiving electrons to form hydrogen molecules. Ion H+ dipilih untuk dinyahcaskan dengan menerima elektron membentuk molekul hidrogen . – Half equation / Persamaan setengah: 2H+ + 2e H2 . 3 Describe an experiment to determine the product of electrolysis copper(II) sulphate solution with carbon electrode. Your answer should include the observation, confirmatory test for the product at the anode and half equation at the electrode. Huraikan satu eksperimen untuk menentukan hasil elektrolisis larutan kuprum(II) sulfat menggunakan elektrod karbon. Dalam jawapan anda perlu disertakan pemerhatian, ujian pengesahan untuk hasil yang terbentuk di anod dan persamaan setengah bagi tindak balas yang berlaku di elektrod. Answer / Jawapan: Apparatus / Radas : Battery/powersupply,carbonelectrodes,wire,electrolyticcell,testtube,Ammeter[fromalabelleddiagram] Bateri/bekalan kuasa, elektrod karbon, wayar, sel elektrolisis, tabung uji, ammeter (dari rajah berlabel) Material / Bahan : 1 mol dm–3 copper(II) sulphate solution / Larutan kuprum(II) sulfat 1 mol dm–3 Carbon electrodes Elektrod karbon Copper(II) sulphate solution Larutan kuprum(II) sulfat Procedure / Langkah: (a) Pour 1 mol dm–3 copper(II) sulphate solution in the electrolytic cell until it is half full . Masukkan larutan kuprum(II) sulfat 1 mol dm–3 ke dalam sel elektrolisis sehingga separuh penuh . (b) The apparatus is set up as shown in the diagram. Fill the test tube with copper(II) sulphate solution and invert the test tube on the anode . Radas disusunkan seperti dalam gambar rajah. Isi tabung uji dengan larutan kuprum(II) sulfat dan terbalikkan tabung uji itu pada anod . (c) Carbon electrodes are connected to batteries using connecting wire. Elektrod karbon disambung kepada bateri menggunakan wayar penyambung. (d) Collect the gas produced at the anode . Kumpulkan gas yang terhasil di anod . (e) Gas produced at the anode is tested with a glowing wooden splinter . Gas yang terhasil di anod diuji dengan kayu uji berbara . 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 108 9/18/15 5:05 PM
  14. 14. MODULE • Chemistry FORM 4 109 © Nilam Publication Sdn. Bhd. 5UNIT Observation and half equation / Pemerhatian dan persamaan setengah: Electrodes Elektrod Observation Pemerhatian Confirmatory test Ujian pengesahan Half equation Persamaan setengah Cathode Katod Brown solid deposited. Pepejal perang terenap. – Cu2+ + 2e Cu Anode Anod Colourless gas bubbles are released. Gelembung gas tak berwarna dibebaskan. – Insert the glowing wooden splinter into the test tube. Masukkan kayu uji berbara ke dalam tabung uji. – The glowing wooden splinter is lighted up. Kayu uji berbara menyala. 4OH– 2H2O + O2 + 4e 4 Copper(II) sulphate solution is electrolysed using copper electrodes. Larutan kuprum(II) sulfat dielektrolisis dengan menggunakan elektrod kuprum. (a) Write the formula of all the anions present in the solution. / Tuliskan formula semua anion yang terdapat dalam larutan itu. SO4 2– , OH– (b) Write the half equation for the reaction at the / Tuliskan persamaan setengah untuk tindak balas di (i) anode / anod : Cu Cu2+ + 2e (ii) cathode / katod : Cu2+ + 2e Cu (c) (i) From your observations, what happen to the intensity of the blue colour of the copper(II) sulphate solution during electrolysis? / Daripada pemerhatian anda, apakah yang berlaku ke atas keamatan warna biru larutan kuprum(II) sulfat semasa proses elektrolisis? The intensity of the blue colour of copper(II) sulphate remains unchanged. Keamatan warna biru kuprum(II) sulfat tidak berubah. (ii) Explain your answer. / Jelaskan jawapan anda. The number of copper(II) ions become copper atoms at the cathode is equal to the number of copper atoms become copper(II) ions at the anode. Bilangan ion kuprum(II) menjadi atom kuprum di katod adalah sama dengan bilangan atom kuprum menjadi ion kuprum(II) di anod. (d) If the experiment is repeated with the copper electrodes being replaced by carbon electrodes, state the name of the products formed at the Jika eksperimen diulangi dengan menggantikan elektrod kuprum dengan elektrod karbon, namakan hasil yang terbentuk di (i) anode / anod : Oxygen / Oksigen (ii) cathode / katod: Copper / Kuprum 5 The diagram below shows the set-up of apparatus of an electrolytic cell. Rajah di bawah menunjukkan susunan radas bagi sel elektrolisis. Copper(II) nitrate solution Larutan kuprum(II) nitrat Carbon electrode P Elektrod karbon P Carbon electrode Q Elektrod karbon Q (a) Write the formula of all ions present in copper(II) nitrate solution. Tuliskan formula semua ion yang hadir dalam larutan kuprum(II) nitrat. Cu2+ , NO3 – , H+ , OH– (b) Write the half equation for the reaction at the / Tuliskan persamaan setengah untuk tindak balas di electrode P / elektrod P : Cu2+ + 2e Cu electrode Q / elektrod Q : 4OH– 2H2O + O2 + 4e (c) (i) What is the colour of copper(II) nitrate / Apakah warna larutan kuprum(II) nitrat? Blue / Biru (ii) What happens to the intensity of the colour of copper(II) nitrate solution? Explain your answer. Apakah yang berlaku kepada keamatan warna larutan kuprum(II) nitrat? Jelaskan jawapan anda. Theintensityofthebluecolourofcopper(II)nitratesolutiondecreases.TheconcentrationofCu2+ decreasesbecausecopper(II) ions receive electrons to form copper atom at the cathode. /Keamatan warna biru larutan kuprum(II) nitrat berkurang. Kepekatan ion Cu2+ berkurang kerana ion kuprum(II) menerima elektron untuk membentuk atom kuprum di katod. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 109 9/18/15 5:05 PM
  15. 15. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 110 5UNIT Electrolysis in Industry / Elektrolisis dalam Industri 1 Three uses of electrolysis in industries are / Tiga kegunaan elektrolisis dalam industri ialah: Application Aplikasi Example Contoh Electrolyte Elektrolit Anode / Half equation Anod / Persamaan setengah Cathode / Half equation Katod / Persamaan setengah (a) Electroplating Penyaduran logam Silver electroplating Penyaduran perak Silver nitrate solution Larutan argentum nitrat Anode / Anod: Silver metal / Logam argentum Half equation / Persamaan setengah: Ag Ag+ + e Cathode / Katod: Metaltobeelectroplated/Logamyangdisadur Half equation / Persamaan setengah: Ag+ + e Ag (b) Purification of metal Penulenan logam Purification of copper Penulenan kuprum Copper(II) sulphate solution Larutan kuprum(II) sulfat Anode / Anod: Impure copper / Kuprum tak tulen Half equation / Persamaan setengah: Cu Cu2+ + 2e Cathode / Katod: Pure copper / Kuprum tulen Half equation / Persamaan setengah: Cu2+ + 2e Cu (c) Metal extraction Pengekstrakan logam Extraction of aluminium Pengekstrakan aluminium Molten aluminium oxide Aluminium oksida lebur Anode / Anod: Carbon / Karbon Half equation / Persamaan setengah: 2O2– O2 + 4e Cathode / Katod: Carbon / Karbon Half equation / Persamaan setengah: Al3+ + 3e Al 2 The following diagram shows the aluminium extraction process. / Rajah di bawah menunjukkan proses pengekstrakan aluminium. Substance Z / Bahan Z Substance Y Bahan Y Substance W Bahan W Substance X + cryolite Bahan X + kriolit (a) State the name of the following substances: / Nyatakan nama bahan-bahan berikut: W : Liquid aluminium / Cecair aluminium X : Molten aluminium oxide / Leburan aluminium oksida Y : Carbon / Karbon Z : Carbon / Karbon (b) Which substance acts as anode and cathode? / Bahan yang manakah bertindak sebagai anod dan katod? Anode / Anod: Z Cathode / Katod: Y (c) State the name of the product at anode and cathode. / Namakan hasil yang diperoleh di anod dan katod. Anode / Anod: Oxygen / Oksigen Cathode / Katod: Aluminium / Aluminium (d) Write the ionic equation for the reactions at / Tuliskan persamaan ion bagi tindak balas yang berlaku di Anode / Anod: 2O2– O2 + 4e Cathode / Katod: Al3+ + 3e Al (e) Why is cryolite added to X? / Mengapakan kriolit ditambah ke dalam X? To reduce the melting point of aluminium oxide (from 2 045 °C to 900 °C ). Untuk menurunkan takat lebur aluminium oksida (dari 2 045 °C ke 900 °C). 3 The diagram below shows the set-up of apparatus used in the purification of copper. Rajah di bawah menunjukkan susunan radas yang digunakan untuk proses penulenan kuprum. Electrode X Elektrod X Electrode Y Elektrod Y Electrolyte Z Elektrolit Z 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 110 9/18/15 5:05 PM
  16. 16. MODULE • Chemistry FORM 4 111 © Nilam Publication Sdn. Bhd. 5UNIT (a) State the name of the substance used as: / Nyatakan nama bahan yang dijadikan sebagai: electrode X / elektrod X : Impure copper / Kuprum tidak tulen electrode Y / elektrod Y : Pure copper / Kuprum tulen electrolyte Z / elektrolit Z : Copper(II) sulphate solution / Larutan kuprum(II) sulfat (b) Tuliskan persamaan setengah yang berlaku di / Write the half equation that occur at the electrode X / elektrod X : Cu Cu2+ + 2e electrode Y / elektrod Y : Cu2+ + 2e Cu (c) What are the observations at the / Apakah pemerhatian di electrode X / elektrod X : Electrode becomes thinner / Elektrod semakin nipis electrode Y / elektrod Y : Brown solid deposited / Logam perang terenap 4 To purify an impure metal / Untuk menulenkan logam tak tulen: (a) The impure metal is used as the anode. / Logam tak tulen dijadikan sebagai anod. (b) The pure metal is used as the cathode. / Logam tulen dijadikan sebagai katod. (c) The electrolyte used is a salt solution containing the ions of the purifying metal. Elektrolit adalah larutan garam yang mengandungi ion logam yang hendak ditulenkan. 5 A student intends to electroplate an iron spoon with copper. Describe a laboratory experiment to electroplate the iron spoon. Your answer should involve the following: / Seorang pelajar bercadang untuk menyadurkan sebatang sudu besi dengan kuprum. Huraikan satu eksperimen di dalam makmal untuk menyadur sebatang sudu besi. Jawapan anda perlu mengandungi: – A labelled diagram showing the set-up of apparatus. / Rajah berlabel menunjukkan susunan radas. – Procedure. / Kaedah. – Half equation for the reactions at both electrodes. / Persamaan setengah untuk tindak balas di kedua-dua elektrod. – Observation at both electrodes. / Pemerhatian di kedua-dua elektrod. Answer / Jawapan: Copper Kuprum Copper(II) nitrate solution Larutan kuprum(II) nitrat Iron spoon Sudu besi Procedure / Kaedah: (a) Copper plate and iron spoon are cleaned with sand paper . Kepingan kuprum dan sudu besi dibersihkan dengan kertas pasir . (b) Copper(II) nitrate solution is poured into a beaker until half full . Larutan kuprum(II) nitrat dituangkan ke dalam bikar sehingga separuh penuh . (c) Iron spoon is then connected to the negative terminal of battery while the copper plate is connected to the positive terminal of the battery using connecting wire. // Iron spoon is made as cathode while copper plate is made as anode. Sudu besi disambungkankepadaterminalnegatifbateridan kepingan kuprum disambungkankepadaterminal positif bateri menggunakan wayar penyambung. // Sudu besi dijadikan katod dan kepingan kuprum dijadikan anod. (d) The iron spoon and the copper plate are dipped in the copper(II) nitrate solution as shown in the diagram. Sudu besi dan plat kuprum dicelup ke dalam larutan kuprum(II) nitrat seperti ditunjukkan dalam rajah. (e) The circuit is completed / Litar dilengkapkan . (f) Half equation at the cathode / Persamaan setengah di katod: Cu2+ + 2e Cu . (g) Observation of the cathode: Brown solid is deposited / Pemerhatian di katod: pepejal perang terenap. (h) Half equation at the anode / Persamaan setengah di anod: Cu Cu2+ + 2e . (i) Observation of the anode: Copper plate becomes thinner / Pemerhatian di anod: Kuprum menipis . 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 111 9/18/15 5:05 PM
  17. 17. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 112 5UNIT 6 To electroplate an object with metal / Untuk menyadur sesuatu objek dengan logam: (a) The metal object to be electroplated is made to be cathode / Objek yang hendak disadur dijadikan katod . (b) The electroplating metal is made to be anode / Logam penyadur dijadikan anod . (c) The electrolyte used is an aqueous salt solution containing the ions of the electroplating metal. Elektrolit yang digunakan adalah larutan akueus garam yang mengandungi ion logam penyadur. Electrochemical Series / Siri Elektrokimia 1 Electrochemical Series is an arrangement of metals according to their tendency to release electrons to form a positive ion. Siri Elektrokimia ialah susunan logam mengikut kecenderungan melepaskan elektron membentuk ion bercas positif . 2 The position of metal atoms in Electrochemical Series / Kedudukan atom logam dalam Siri Elektrokimia: K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, Cu, Ag Tendency of metal atom to release/donate electrons increases (electropositivity increases) Kecenderungan untuk atom logam melepaskan/menderma elektron bertambah (keelektropositifan bertambah) 3 The position of metal ions (cation) in the Electrochemical Series / Kedudukan ion logam (kation) dalam Siri Elektrokimia: K+ , Na+ , Ca2+ , Mg2+ , Al3+ , Zn2+ , Fe2+ , Sn2+ , Pb2+ , *H+ , Cu2+ , Ag+ Tendency of metal ion (cation) to receive/gain electrons increases Kecenderungan untuk ion logam (kation) untuk menerima elektron bertambah * H+ is also in the series of ion because it is present in aqueous solution of any electrolyte (salt solution/acid/alkali) * H+ juga terdapat dalam siri ion kerana kehadiran ion H+ dalam elektrolit larutan akueus (larutan garam/asid/alkali) Metal Displacement Reaction / Tindak Balas Penyesaran Logam 1 The metal which is situated at a higher position (higher tendency to release electron) in the Electrochemical Series is able to displace metals below it from its salt solution . Logam yang berada di kedudukan atas (kecenderungan melepaskan elektron yang tinggi) dalam Siri Elektrokimia dapat menyesarkan logam yang di bawahnya daripada larutan garam logam tersebut. 2 Example / Contoh: Experiment / Eksperimen Observation / Pemerhatian Remark / Catatan Copper Kuprum Silver nitrate solution Larutan argentum nitrat – Copper strip becomes thinner . Kepingan kuprum menipis . – A grey solid deposited. Pepejal kelabu terenap. – The colourless solution turns blue. Larutan tidak berwarna bertukar menjadi biru. Inference / Inferens: – The grey solid is silver . Pepejal kelabu adalah argentum . – The blue solution is copper(II) nitrate . Larutan biru adalah kuprum(II) nitrat . Explanation / Penerangan: – Silver ion receives electrons to form silver atom. Ion argentum menerima elektron membentuk atom argentum . – Copper atom releases electrons to form copper(II) ion . Atom kuprum melepaskan elektron membentuk ion kuprum(II) . – Copper has displaced silver from silver nitrate solution. Kuprum telah menyesarkan argentum dari larutan argentum nitrat. Cu + 2AgNO3 Cu(NO3)2 + 2Ag . – Copper is more electropositive than silver// Copper is above silver in the Electrochemical Series of metal. Kuprum adalah lebih elektropositif daripada argentum //Kuprum terletak di atas argentum dalam Siri Elektrokimia logam. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 112 9/18/15 5:05 PM
  18. 18. MODULE • Chemistry FORM 4 113 © Nilam Publication Sdn. Bhd. 5UNIT Magnesium Magnesium Copper(II) sulphate solution Larutan kuprum(II) sulfat Magnesium strip becomes thinner . Kepingan magnesium menipis . The brown solid deposited. Pepejal perang terenap. The blue solution turns colourless. Larutan biru bertukar menjadi tidak berwarna. Inference / Inferens: – The brown solid is copper . Pepejal perang adalah kuprum . – The colourless solution is magnesium sulphate . Larutan tidak berwarna adalah magnesium sulfat . Explanation / Penerangan: – Copper(II) ion receives electrons to form copper atom. Ion kuprum(II) menerima elektron membentuk atom kuprum. – Magnesium atom releases electrons to form magnesium ion . Atom magnesium melepaskan elektron membentuk ion magnesium . – Magnesium has displaced copper from copper(II) sulphate solution. Magnesium telah menyesarkan kuprum dari larutan kuprum(II) sulfat. Mg + CuSO4 MgSO4 + Cu . – Magnesium is more electropositive than copper// Magnesium is above copper in the Electrochemical Series of metal. Magnesium adalah lebih elektropositif daripada kuprum// Magnesium terletak di atas kuprum dalam Siri Elektrokimia logam. Copper / Kuprum Zinc sulphate solution Larutan zink sulfat No observable changes. Tiada perubahan yang dapat diperhatikan. Inference / Inferens: No reaction occur. Tiada tindak balas berlaku. Explanation / Penerangan: – Copper cannot displace zinc from zinc sulphate solution. Kuprum tidak boleh menyesarkan zink daripada larutan zink sulfat. – Copper is less electropositive than zinc// Copper is below zinc in the Electrochemical Series of metal. Kuprum adalah kurang elektropositif daripada zink // Kuprum terletak di bawah zink dalam Siri Elektrokimia logam. Voltaic Cell (Chemical Cell) / Sel Ringkas (Sel Kimia) 1 A cell that produces electrical energy when chemical reactions occur in it. Sel yang menghasilkan tenaga elektrik apabila berlaku tindak balas kimia di dalamnya. 2 Energy change in voltaic cell is from chemical energy to electrical energy . Perubahan tenaga dalam sel ringkas ialah dari tenaga kimia kepada tenaga elektrik . 3 Produced when two different metals are dipped in an electrolyte and are connected by an external circuit . Terhasil apabila dua logam berlainan dicelup dalam elektrolit dan disambung dengan litar luar . 4 The voltage of chemical cell depends on the distance between the two metals in the Electrochemical Series, where the further the distance between them, the higher is the voltage. Voltan sel kimia bergantung pada jarak antara dua logam dalam Siri Elektrokimia di mana semakin jauh dua logam dalam Siri Elektrokimia, semakin tinggi voltannya. 5 A more electropositive metal becomes the negative terminal of the cell. A less electropositive metal becomes the positive terminal: Logam yang lebih elektropositif akan menjadi terminal negatif sel. Logam yang kurang elektropositif akan menjadi terminal positif sel: 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 113 9/18/15 5:05 PM
  19. 19. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 114 5UNIT Electrical current produced is detected by the galvanometer (Chemical energy Electrical energy) Arus elektrik terhasil dikesan oleh galvanometer (Tenaga kimia Tenaga elektrik) Negative terminal / Terminal negatif : • More electropositive metal. Logam lebih elektropositif. • Metal atom will release electrons that will flow through the external circuit. Metal atom becomes metal ion (becomes thinner). Atom logam akan melepaskan elektron yang akan mengalir di litar luar. Atom logam menjadi ion logam (semakin nipis). Positive terminal / Terminal positif : • Less electropositive metal. Logam kurang elektropositif. • The electrons that flow from the external circuit are received by the positive ion in the electrolyte through this terminal. Elektron yang akan mengalir dari litar luar diterima oleh ion positif dalam elektrolit melalui terminal ini. _ + G _ + V 6 Example of simple voltaic cell / Contoh voltan sel ringkas: Magnesium Magnesium Copper(II) sulphate solution Larutan kuprum(II) sulfat Copper Kuprum _ + G _ + V (a) Magnesium electrode is the negative terminal because magnesium is more electropositive than copper : Elektrod magnesium adalah terminal negatif kerana magnesium lebih elektropositif daripada kuprum : – Magnesium atom releases electrons to form magnesium ion, Mg2+ . Atom magnesium melepaskan elektron untuk membentuk ion magnesium, Mg2+ . – Half equation/ Persamaan setengah: Mg Mg2+ + 2e . – Magnesium electrode becomes thinner / Elektrod magnesium menjadi nipis . – Electron flows through external circuit to the copper electrode. Elektron mengalir melalui litar luar ke elektrod kuprum . (b) Copper electrode is the positive terminal because copper is less electropositive than magnesium : Elektrod kuprum adalah terminal positif kerana kuprum kurang elektropositif daripada magnesium : – Electrons from magnesium flow through external circuit to copper electrode. Elektron dari magnesium mengalir melalui litar luar ke elektrod kuprum. – Copper(II) ion in the electrolyte receives electron to form copper atom. Ion kuprum(II) dalam elektrolit menerima elektron untuk membentuk atom kuprum. – Half equation / Persamaan setengah : Cu2+ + 2e Cu . – Brown solid is deposited on the surface of copper electrode. Pepejal perang terenap di permukaan elektrod kuprum. (c) The concentration of copper(II) sulphate decreases because copper(II) ions discharged to form copper atom at the positive terminal. The intensity of blue colour of copper(II) sulphate solution decreases. Kepekatan larutan kuprum(II) sulfat berkurang kerana ion kuprum(II) dinyahcaskan kepada atom kuprum. Keamatan warna biru larutan kuprum(II) sulfat berkurang. If the magnesium metal is replaced with a zinc metal, the voltage reading decreases because zinc is nearer to copper in the Electrochemical Series. Jika logam magnesium digantikan dengan logam zink, bacaan voltan akan berkurang kerana zink lebih dekat dengan kuprum dalam Siri Elektrokimia. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 114 9/18/15 5:05 PM
  20. 20. MODULE • Chemistry FORM 4 115 © Nilam Publication Sdn. Bhd. 5UNIT 7 Daniell cell / Sel Daniell (a) It is an example of voltaic cell which consists of zinc electrode dipped in zinc sulphate solution, copper electrode dipped in copper(II) sulphate solution and connected by a salt bridge or porous pot. Merupakan satu contoh sel kimia yang terdiri daripada elektrod zink yang dicelup ke dalam larutan zink sulfat, elektrod kuprum dicelupkan ke dalam larutan kuprum(II) sulfat dan dihubungkan dengan titian garam atau pasu berliang. Zn / ZnSO4 // CuSO4 / Cu (b) The function of porous pot or salt bridge is to allow the flow of ions through it so that the electric circuit is completed. Fungsi pasu berliang atau titian garam adalah untuk membenarkan ion-ion mengalir melaluinya dan melengkapkan litar. (c) The diagram below shows the set-up of apparatus of Daniell cell. Rajah di bawah menunjukkan susunan radas bagi sel Daniell. Copper Kuprum Zinc / Zink Zinc sulphate solution Larutan zink sulfat Porous pot Pasu berliang Copper(II) sulphate solution Larutan kuprum(II) sulfat Copper Kuprum Zinc Zink Zinc sulphate solution Larutan zink sulfat Copper(II) sulphate solution Larutan kuprum(II) sulfat Sulphuric acid Asid sulfurik (d) Zinc electrode is the negative terminal because zinc is more electropositive than copper : Elektrod zink adalah terminal negatif kerana zink adalah lebih elektropositif daripada kuprum : – Zinc atom releases electron to form zinc ion, Zn2+ . Atom zink melepaskan elektron untuk membentuk ion zink, Zn2+ . – Half equation / Persamaan setengah : Zn Zn2+ + 2e . – Zinc electrode becomes thinner / Elektrod zink menjadi nipis . – Electrons flow through external circuit to the copper electrode. Elektron mengalir melalui litar luar ke elektrod kuprum . (e) Copper electrode is the positive terminal because copper is less electropositive than zinc : Elektrod kuprum adalah terminal positif kerana kuprum kurang elektropositif daripada zink : – Electrons from zinc electrode flow through external circuit to copper electrode. Elektron dari zink mengalir melalui litar luar ke elektrod kuprum. – Copper(II) ion in the electrolyte receives electron to form copper atom. Ion kuprum(II) dalam elektrolit menerima elektron untuk membentuk atom kuprum. – Half equation / Persamaan setengah : Cu2+ + 2e Cu . – Brown solid is deposited on the surface of copper electrode. Pepejal perang terenap di permukaan elektrod kuprum. (f) The concentration of copper(II) sulphate solution decreases because copper(II) ions are discharged to copper atoms. The intensity of blue colour of copper(II) sulphate solution decreases. Kepekatan larutan kuprum(II) sulfat berkurang kerana ion kuprum(II) telah dinyahcaskan kepada atom kuprum. Keamatan warna biru larutan kuprum(II) sulfat berkurang. (g) If zinc metal is replaced with a magnesium metal and zinc sulphate solution is replaced with magnesium sulphate solution, the voltage reading increases because magnesium is further from copper in the Electrochemical Series. Jika logam zink digantikan dengan logam magnesium dan larutan zink sulfat digantikan dengan larutan magnesium sulfat, bacaan voltan bertambah kerana jarak antara magnesium dengan kuprum lebih jauh daripada jarak antara zink dengan kuprum dalam Siri Elektrokimia. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 115 9/18/15 5:05 PM
  21. 21. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 116 5UNIT 8 Four main uses of the Electrochemical Series: Empat kegunaan utama Siri Elektrokimia: (a) To predict the terminal of chemical cell Untuk meramalkan terminal sel kimia – The more electropositive metal is the negative terminal of the cell. Logam yang lebih elektropositif ialah terminal negatif sel. – The less electropositive metal is the positive terminal of the cell. Logam yang kurang elektropositif ialah terminal positif sel. (b) To predict the voltage of chemical cell Untuk meramalkan voltan sel kimia – The further the distance between two metals in the Electrochemical Series, the higher is the voltage of the chemical cell. Semakin jauh jarak antara dua logam dalam Siri Elektrokimia, semakin tinggi bacaan voltan sel kimia. (c) To predict the metal displacement reactions Untuk meramalkan tindak balas penyesaran logam – The more electropositive metal can displace a less electropositive metal from its salt solution. – Logam yang lebih elektropositif dapat menyesarkan logam yang kurang elektropositif daripada larutan garamnya. (d) To predict the selected ion to be discharged at the electrode in an electrolysis Untuk meramalkan pemilihan ion untuk dinyahcas di elektrod dalam proses elektrolisis 1 The table below shows the results of an experiment to construct the Electrochemical Series through the ability of metals to displace other metals from their salt solution. Jadual di bawah menunjukkan keputusan eksperimen untuk membina Siri Elektrokimia berdasarkan keupayaan suatu logam untuk menyesarkan logam lain dari larutan garamnya. Experiment I / Eksperimen I Experiment II / Eksperimen II Zinc / Zink P nitrate solution Larutan P nitrat Zinc / Zink R nitrate solution Larutan R nitrat Metal P is displaced, blue colour solution turns colourless. Logam P disesarkan, larutan biru bertukar menjadi tanpa warna. No reaction. Tiada tindak balas. (a) Based on the results in the table, arrange metal P, zinc and R in descending order of electropositivity. Berdasarkan keputusan dalam jadual, susunkan logam P, zink dan R dalam tertib menurun keelektropositifan. R, Zn, P (b) Based on the observation in Experiment I, / Berdasarkan pemerhatian dalam Eksperimen I, (i) name a suitable metal for P. / namakan logam yang sesuai bagi P. Copper / Kuprum (ii) zinc can displace metal P from P nitrate solution. Explain. zink boleh menyesarkan logam P daripada larutan P nitrat. Terangkan. Zinc is more electropositive than P. Zink lebih elektropositif daripada P. (iii) write the chemical equation for the reaction. tuliskan persamaan kimia untuk tindak balas. Zn + Cu(NO3)2 Zn(NO3)2 + Cu Exercise / Latihan 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 116 9/18/15 5:05 PM
  22. 22. MODULE • Chemistry FORM 4 117 © Nilam Publication Sdn. Bhd. 5UNIT 2 The diagram below shows the set-up of the apparatus to arrange metals W, X, Y and Z based on the potential difference of the metals. Rajah di bawah menunjukkan susunan radas bagi eksperimen untuk menentukan kedudukan logam W, X, Y dan Z berdasarkan beza upaya logam. Metal electrode Elektrod logam Metal electrode Elektrod logam Electrolyte / Elektrolit V The table below shows the results of the experiment. Jadual di bawah menunjukkan keputusan eksperimen. Pair of metals Pasangan logam Potential difference (V) Beza keupayaan (V) Negative terminal Terminal negatif W and X W dan X 0.50 X X and Y X dan Y 0.30 Y W and Z W dan Z 1.10 Z (a) Arrange metals W, X, Y and Z in descending order of the electropositivity of metal. Susunkan logam W, X, Y dan Z dalam tertib menurun keelektropositifan logam. Z, Y, X, W (b) (i) Metals X and Z are used as electrodes in the diagram. State which metal acts as positive terminal. Logam X dan Z digunakan sebagai elektrod dalam rajah. Nyatakan logam yang manakah akan bertindak sebagai terminal positif. Metal X / Logam X (ii) Give reason for your answer in (b)(i). Berikan sebab untuk jawapan anda di (b)(i). Metal X is less electropositive than metal Z. Logam X kurang elektropositif daripada logam Z. (c) Predict the voltage of the cell in (b)(i). Ramalkan nilai voltan dalam sel di (b)(i). 0.6 V 3 The diagram below shows the set-up of apparatus for two types of cell. Rajah di bawah menunjukkan susunan radas untuk dua jenis sel. Cell X / Sel X Cell Y / Sel Y Copper Kuprum Copper Kuprum Zinc Zink Copper(II) sulphate solution Larutan kuprum(II) sulfat 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 117 9/18/15 5:05 PM
  23. 23. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 118 5UNIT Complete the following table to compare cell X and cell Y: Lengkapkan jadual berikut untuk membandingkan sel X dan sel Y: Description Perkara Cell X Sel X Cell Y Sel Y Type of cell Jenis sel Electrolytic cell / Sel elektrolisis Chemical cell / Sel kimia The energy change Perubahan tenaga Electrical energy Chemical energy Tenaga elektrik Tenaga kimia Chemical energy Electrical energy Tenaga kimia Tenaga elektrik Ion presence in the electrolyte Ion hadir dalam elektrolit Cu2+ , H+ , SO4 2– , OH– Cu2+ , H+ , SO4 2– , OH– Electrode Elektrod Anode / Anod: Copper / Kuprum Cathode / Katod: Copper / Kuprum Negative terminal / Terminal negatif : Zinc / Zink Positive terminal / Terminal positif : Copper / Kuprum Half equation Persamaan setengah Anode / Anod: Cu Cu2+ + 2e Cathode / Katod: Cu2+ + 2e Cu Negative terminal / Terminal negatif : Zn Zn2+ + 2e Positive terminal / Terminal positif : Cu2+ + 2e Cu Observation Pemerhatian Anode / Anod: Copper electrode becomes thinner Elektrod kuprum semakin nipis Cathode / Katod: Brown solid deposited / Pepejal perang terenap Electrolyte / Elektrolit: Intensity of blue colour of copper(II) sulphate solution remains unchanged / Keamatan warna biru larutan kuprum(II) sulfat tidak berubah Negative terminal / Terminal negatif : Zinc electrode becomes thinner/Elektrod zink semakin nipis Positive terminal / Terminal positif : Brown solid deposited / Pepejal perang terenap Electrolyte / Elektrolit: Intensity of blue colour of copper(II) sulphate solution decreases Keamatan warna biru larutan kuprum(II) sulfat semakin berkurang 4 The diagram below shows the set-up of apparatus for an experiment. Rajah di bawah menunjukkan susunan radas bagi suatu eksperimen. Zinc / Zink Cell A / Sel A Cell B / Sel B Copper(II) sulphate solution Larutan kuprum(II) sulfat Copper(II) sulphate solution Larutan kuprum(II) sulfat Zinc sulphate solution Larutan zink sulfat V Copper Kuprum Copper Kuprum Porous pot Pasu berliang Anode / Anod+– Cathode / Katod (a) In the above diagram, label / Dalam gambar rajah di atas, label (i) the positive terminal and negative terminal in Cell A, terminal positif dan terminal negatif bagi Sel A, (ii) anode and cathode in Cell B. anod dan katod bagi Sel B. (b) What is the energy change in Cell A and Cell B? Apakah perubahan tenaga dalam Sel A dan Sel B? Cell A / Sel A : Chemical energy to electrical energy / Tenaga kimia kepada tenaga elektrik Cell B / Sel B : Electrical energy to chemical energy / Tenaga elektrik kepada tenaga kimia (c) What is the function of the porous pot in Cell A? Apakah fungsi pasu berliang dalam Sel A? To allow the movement of ions through it. / Untuk membolehkan ion mengalir melaluinya. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 118 9/18/15 5:05 PM
  24. 24. MODULE • Chemistry FORM 4 119 © Nilam Publication Sdn. Bhd. 5UNIT (d) Referring to Cell A. Merujuk kepada Sel A. (i) What is the observation at zinc electrode? Apakah pemerhatian di elektrod zink? Zinc electrode becomes thinner. / Elektrod zink menipis. (ii) Write the half equation for the reaction at zinc electrode. Tuliskan persamaan setengah untuk tindak balas di elektrod zink. Zn Zn2+ + 2e (iii) What is the observation at copper electrode? Apakah pemerhatian di elektrod kuprum? Brown solid deposited. / Pepejal perang terenap. (iv) Write the half equation for the reaction at copper electrode. Tuliskan persamaan setengah untuk tindak balas di elektrod kuprum. Cu2+ + 2e Cu (v) After 30 minutes, what is the colour change of the copper(II) sulphate solution? Explain why. Selepas 30 minit, apakah perubahan warna larutan kuprum(II) sulfat? Jelaskan mengapa. The intensity of blue colour decreases. Copper(II) ions are discharged to form copper atoms. Concentration of copper(II) ions in copper(II) sulphate solution decreases. Keamatan warna biru berkurang. Ion kuprum(II) menerima elektron untuk membentuk atom kuprum. Kepekatan ion kuprum(II) dalam larutan kuprum(II) sulfat berkurangan. (e) Referring to Cell B. Merujuk kepada Sel B. (i) What is the observation at the anode? Apakah pemerhatian di anod? Copper electrode becomes thinner. / Elektrod kuprum menipis (ii) Write the half equation for the reaction at the anode. Tuliskan persamaan setengah untuk tindak balas di anod. Cu Cu2+ + 2e (iii) What is the observation at the cathode? Apakah pemerhatian di katod? Brown solid deposited. / Pepejal perang terenap (iv) Write the half equation for the reaction at cathod. Tuliskan persamaan setengah untuk tindak balas di katod. Cu2+ + 2e Cu (f) The intensity of blue colour of copper(II) sulphate solution in the Cell B remains unchanged during the experiment. Explain why. Keamatan warna biru larutan kuprum(II) sulfat dalam Sel B tidak berubah semasa eksperimen. Jelaskan mengapa. The concentration of copper(II) sulphate remain unchanged. The rate of copper(II) ions discharged to copper atom at the cathode equals to the rate of copper atoms form copper(II) ions at the anode. Kepekatan kuprum(II) sulfat tidak berubah. Kadar ion kuprum(II) menyahcas kepada atom kuprum di katod sama dengan kadar atom kuprum mengion membentuk ion kuprum(II) di anod. 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 119 9/18/15 5:05 PM
  25. 25. MODULE • Chemistry FORM 4 © Nilam Publication Sdn. Bhd. 120 5UNIT 1 Which of the following is an electrolyte? Antara berikut, yang manakah adalah elektrolit? A Glacial ethanoic acid Asid etanoik glasial B Molten naphthalene Naftalena lebur 3 C Aqueous solution of zinc chloride Larutan akueus zink klorida D Hydrogen chloride in methylbenzene Hidrogen klorida dalam metilbenzena 2 The diagram below shows the set-up of apparatus used to electrolyse substance X. Rajah di bawah menunjukkan susunan radas untuk elektrolisis bahan X. Carbon electrodes Elektrod karbon Substance X Bahan X Heat Panaskan Which of the following compounds can light up the bulb when used as substance X? Antara berikut, yang manakah boleh menyalakan mentol apabila digunakan sebagai bahan X? A Copper(II) nitrate / Kuprum(II) nitrat 3 B Lead(II) iodide / Plumbum(II) iodida C Zinc carbonate / Zink karbonat D Sodium carbonate / Natrium karbonat 3 The diagram below shows the set-up of apparatus for electrolysis of copper(II) sulphate solution. Rajah di bawah menunjukkan susunan radas untuk elektrolisis larutan kuprum(II) sulfat. Copper electrode X Elektrod kuprum X Copper electrode Y Elektrod kuprum Y Copper(II) sulphate solution Larutan kuprum(II) sulfat What can be observed at the electrodes X and Y after 30 minutes? Apakah yang dapat diperhatikan pada elektrod X dan Y selepas 30 minit? X Y 3 A Copper electrode becomes thinner Elektrod kuprum semakin nipis Copper electrode becomes thicker Elektrod kuprum semakin tebal B Copper electrode becomes thinner / Elektrod kuprum semakin nipis Gas bubbles are released Gelembung gas dibebaskan C Copper electrode becomes thicker Elektrod kuprum semakin tebal Copper electrode becomes thinner Elektrod kuprum semakin nipis D Gas bubbles are released Gelembung gas dibebaskan Copper electrode becomes thicker Elektrod kuprum semakin tebal 4 The diagram below shows the set-up of apparatus of an electrolysis process. Rajah di bawah menunjukkan susunan radas untuk proses elektrolisis. Carbon electrode Elektrod karbon Carbon electrode Elektrod karbon Electrolyte Elektrolit P Q Which of the following electrolytes produce oxygen gas at electrode Q / Antara elektrolit berikut, yang manakah membebaskan gas oksigen pada elektrod Q? I 1.0 mol dm–3 hydrochloric acid Asid hidroklorik 1.0 mol dm–3 II 1.0 mol dm–3 sulphuric acid Asid sulfurik 1.0 mol dm–3 III 1.0 mol dm–3 potassium iodide solution Larutan kalium iodida 1.0 mol dm–3 IV 1.0 mol dm–3 nitric acid Asid nitrik 1.0 mol dm–3 A I and II only / I dan II sahaja B II and III only / II dan III sahaja 3 C II and IV only / II dan IV sahaja D II, III and IV only / II, III dan IV sahaja 5 The table below shows the observation of electrolysis of a substance Q using carbon electrode. Jadualdibawahmenunjukkanpemerhatianbagielektrolisis bahan Q menggunakan elektrod karbon. Electrode Elektrod Observation Pemerhatian Anode Anod A greenish-yellow gas released Gas kuning kehijauan terbebas Cathode Katod A colorless gas which burns with a ‘pop’ sound is released / Gas tanpa warna terbakar dengan bunyi ‘pop’ dibebaskan What is substance Q? Apakah bahan Q? 3 A 1.0 mol dm–3 of hydrochloric acid Asid hidroklorik 1.0 mol dm–3 B 1.0 mol dm–3 of sodium nitrate solution Larutan natrium nitrat 1.0 mol dm–3 C 1.0 mol dm–3 of copper(II) chloride solution Larutan kuprum(II) klorida 1.0 mol dm–3 D 1.0 mol dm–3 of magnesium bromide solution Larutan magnesium bromida 1.0 mol dm–3 Objective Questions / Soalan Objektif 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 120 9/18/15 5:05 PM
  26. 26. MODULE • Chemistry FORM 4 121 © Nilam Publication Sdn. Bhd. 5UNIT 6 The diagram below shows the set-up of apparatus of a chemical cell that shows the direction of electron flow from zinc to metal Q. Rajah di bawah menunjukkan susunan radas sel kimia yang menunjukkan arah pengaliran elektron dari zink ke logam Q. Dilute sodium chloride solution Larutan natrium klorida cair Q Zinc Zink What is metal Q? Apakah logam Q? 3 A Copper Kuprum B Calcium Kalsium C Aluminium Aluminium D Magnesium Magnesium 7 The diagram below shows the set-up of apparatus used to purify impure copper by using electrolysis method. Rajah di bawah menunjukkan susunan radas yang digunakan untuk menulenkan kuprum tak tulen dengan menggunakan kaedah elektrolisis. X Y Electrolyte Z Elektrolit Z Which of the following shows the correct position of pure copper, impure copper and electrolyte Z? Antara berikut, yang manakah adalah betul untuk kuprum tulen, kuprum tak tulen dan elektrolit Z? Electrode X Elektrod X Electrode Y Elektrod Y Electrolyte Z Elektrolit Z 3 A Impure copper Kuprum tak tulen Pure copper Kuprum tulen Copper(II) sulphate solution Larutan kuprum(II) sulfat B Pure copper Kuprum tulen Impure copper Kuprum tak tulen Copper(II) sulphate solution Larutan kuprum(II) sulfat C Impure copper Kuprum tak tulen Pure copper Kuprum tulen Sulphuric acid Asid sulfurik D Pure copper Kuprum tulen Impure copper Kuprum tak tulen Sulphuric acid Asid sulfurik 8 The table below shows the information about three voltaic cells. Jadual di bawah menunjukkan maklumat tentang tiga sel kimia. Pair of metals Pasangan logam Positive terminal Terminal positif Potential difference (V) Beza upaya (V) W, Z Z 3.1 X, Y Y 0.3 W, X X 1.8 What is the potential difference of the voltaic cell when metal Y is paired with metal Z? Apakah beza upaya sel kimia apabila logam Y dipasangkan dengan logam Z? 3 A 1.0 V C 2.1 V B 1.3 V D 2.8 V 9 The diagram below shows the set-up of apparatus in a chemical cell and electrolytic cell. Rajah di bawah menunjukkan susunan radas bagi sel kimia dan sel elekrolisis. Copper Kuprum Copper Kuprum Zinc Zink Copper(II) sulphate solution Larutan kuprum(II) sulfat Zinc sulphate solution Larutan zink sulfat P Q R S Which of the following is the observation at electrode R? Antara berikut, yang manakah merupakan pemerhatian pada elektrod R? 3 A Electrode R becomes thinner / Elektrod R semakin nipis B Electrode R becomes thicker / Elektrod R semakin tebal C Acolourless gas is released / Gas tanpa warna terbebas D A brown solid is deposited / Pepejal perang terenap 10 The table below shows the results of an experiment to study the displacement of metal from its solution using other metals. Jadual di bawah menunjukkan keputusan eksperimen untuk mengkaji penyesaran logam daripada larutan garamnya menggunakan logam lain. Metal Logam Nitrate of Q Nitrat bagi Q Nitrate of S Nitrat bagi S P ✓ ✓ Q – ✗ ✓ – reaction occur / tindak balas berlaku ✗ – no reaction / tiada tindak balas Which of the following is the arrangement of metals P, Q and S in ascending order of the tendency of the metals to form ions? Antara berikut, yang manakah adalah susunan logam P, Q dan S dalam susunan menaik kecenderungan logam membentuk ion? A P, S, Q C S, P, Q 3 B Q, S, P D S, Q, P 05 Chap 5 ChemF4 Bil(FSY5p) new.indd 121 9/18/15 5:05 PM

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