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Chapter 6   electrochemistry
 

Chapter 6 electrochemistry

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    Chapter 6   electrochemistry Chapter 6 electrochemistry Presentation Transcript

    • ELECTROCHEMISTRY
    • CHEMICAL SUBSTANCES ELECTROLYTES NON-ELECTROLYTESSubstances that can conduct Substances that cannotelectricity when they are in conduct electricity either inmolten state or aqueous and molten state or aqueousundergo chemical changes Example:Example: Covalent substances Ionic substances (iii) Naphthalene(iii) Dilute acid solution (iv) Sugar solution(iv) Dilute alkaline solution (v) Latex(v) Molten salts (vi) Hydrogen chloride in organic(vi) Aqueous salt solution solvents
    • switch switchCarbon Bulb Bulbelectrodes Carbon electrodes …. …. …. …. …. …. .. … ……….. …. …………. …. …. …. …. …. …. …. … ………. Heat Heat Solid lead (II) iodide Molten lead (II) iodide
    • IN A SOLID STATE •Do not conduct electricity Pb 2+ I- Pb 2+ I- •This is because thePb 2+ I- Pb 2+ I- Pb 2+ ions are held in a Pb 2+ I- Pb 2+ I- fixed crystal lattice.Solid lead (II) iodide •They are held with the strong electrostatic forces of attraction •Do not freely move
    • IN A MOLTEN STATE Pb 2+ Pb 2+ - •Can conduct I I - electricity I- Pb 2+ •This is because the presence of moving ions. The ions are free to move in the molten or aqueous solutionMolten lead (II) iodide
    • ELECTROLYTES AND NON ELECTROLYTESClassify the following chemicals into electrolytes or non- electrolytes Potassium chloride, KCl solution Molten lead (II) bromide, PbBr2 Glucose solution Trichloromethane Molten zinc oxide, ZnO Sodium chloride, NaCl solution Ammonia in tetrachloromethane
    • ELECTROLYSISA process of breaking down the chemical compounds into their constituent elements using electric currentExample: Electric currentMolten aluminium oxide (I) aluminium (s) + oxygen (g) Electric currentCopper (II) chloride (aq) copper (s) + chlorine (g)
    • ELECTROLYTIC CELL e- e- - e e- + (anode) - (cathode)Electrode Electrode …… ……………… ….. …. ….. …… … …. .. . - …….. …… … + … Electrolyte ……………………………………... Anion Cation
    • ELECTROLYTIC CELL The set of apparatus needed to conduct electrolysis It consists of a battery, an electrolyte, and two electrodes (anode and cathode) Anode - the electrode which is connected to the positive terminal of an electric source in the electrolytic cell Cathode - the electrode which is connected to the negative terminal of an electric source in the electrolytic cell
    •  During electrolysis: ANODE CATHODE(POSITIVE ELECTRODE) (NEGATIVE ELECTRODE)Anions (negative ions) Cations (positive ions) willwill be pulled towards be pulled towards thethe anode (positive cathode (negativeelectrode) electrode)At the anode, anions At the cathode, cations willwill be discharged by be discharged by receivingreleasing the electrons the electrons from theto the anode cathode
    • ELECTROLYSIS OF MOLTEN COMPOUNDS
    • QUESTIONS(a) Molten zinc chloride (I) Electric current(b) Molten aluminium (III) bromide Electric current(c) Molten zinc (II) iodide Electric current(d) Molten lead (II) oxide Electric current
    • Example 1 e- e- - e e- + (anode) - (cathode) Carbon Carbonelectrode …… ……………… ….. electrode …. ….. …… … …. .. . …….. …… … … Molten Potassium ……………………………………... Iodide, KI The ions that presents in electrolyte are: (ii) Anion: (iii) Cation:
    • Example 2 e- e- - e e- + (anode) - (cathode) Carbon Carbonelectrode …… ……………… ….. electrode …. ….. …… … …. .. . …….. …… … … ……………………………………... Molten zinc oxide, ZnO The ions that presents in electrolyte are: (ii) Anion: (iii) Cation:
    • Example 3 e- e- - e e- + (anode) - (cathode) Carbon Carbonelectrode …… ……………… ….. electrode …. ….. …… … …. .. . …….. …… … … Molten lead (II) ……………………………………... bromide, PbBr2 The ions that presents in electrolyte are: (ii) Anion: (iii) Cation:
    • Example 4 e- e- - e e- + (anode) - (cathode) Carbon Carbonelectrode …… ……………… ….. electrode …. ….. …… … …. .. . …….. …… … … Molten lead (II) oxide, ……………………………………... PbO The ions that presents in electrolyte are: (ii) Anion: (iii) Cation:
    • Example 5 e- e- - e e- + (anode) - (cathode) Carbon Carbonelectrode …… ……………… ….. electrode …. ….. …… … …. .. . …….. …… … … ……………………………………... Molten zinc (II) chloride, ZnCl2 The ions that presents in electrolyte are: (ii) Anion: (iii) Cation:
    • ELECTROLYSIS OF MOLTEN COMPOUND e- e- - e e- + (anode) - (cathode) Carbon Carbon electrode …… ……………… ….. electrode …. ….. …… … …. .. . …….. …… … … Molten lead (II) ……………………………………... bromide, PbBr2 The ions that presents in electrolyte are: (ii) Anion: (iii) Cation:
    • ELECTROLYSIS OF MOLTEN COMPOUND e- e- e - e- + (anode) - (cathode) Carbon Carbonelectrode …… ……………… ….. electrode Br- Pb2+ …. Br - ….. …… Pb … 2+ …. - Br…….. Pb2+ .. . ……Pb … 2+ … Molten lead (II) Br- ……………………………………... bromide
    • ANODE CATHODE (POSITIVE ELECTRODE) (NEGATIVE ELECTRODE)Br- are attracted to anode Pb2+ are attracted to the cathodeBr- discharge by releasing electrons to theanode Pb2+ discharge by receiving electrons Br- Br + e- (provided by the battery) at the cathode to form neutral lead atoms Neutral atoms form and combine to form neutral bromine molecules The half reaction at cathode can be Br + Br Br2 (g) represented by the half equation Pb2+(l) + 2e- Pb (s) The half reaction at anode can be represented by the half equation 2Br- (l) Br2 (g) + 2e-
    • The Half Equation: 2+ -Cathode: Pb (l) + 2e Pb (s)Anode: 2Br- (l) Br2 (g) + 2e-Overall Equation: Pb2+(l) + 2Br- (l) Pb(s) + Br2 (g)
    • Write the half equation and the overall equation for the electrolysis of these molten compounds :(A) Molten potassium iodide, KI(B) Molten zinc (II) chloride, ZnCl2(C) Molten lead (II) oxide, PbO
    • ELECTROLYSIS OF AQUEOUS SOLUTIONWater molecules in an aqueous solution can slightly dissociate toproduce H+ and OH- H2O H+ (aq) + OH-(aq)So, aqueous solution contains H+ and OH- and electrolyte ionsExamples: Ions present Aqueous Solution Anion Cation NaCl solution Cl- , OH- Na+ , H+ CuSO4 solution HNO3 solution
    • If they are more than one cations or anionsattracted, the choice of ion to be discharged depends on : Positions of the ions in the electrochemical series Concentration of ions in the electrolyte Types of electrodes
    • Electrochemical Series (pg.101) CATIONS ANIONS K+ F- Na+ Ca2+ SO42- Mg2+ NO3- Al 3+ Cl- Zn2+ Fe2+ Br- Sn2+ I- Pb2+ OH- H+ Tendency to Cu2+ discharge Ag+ increases
    • Positions of the ionsin the electrochemical series e- e- e - e- + (anode) - (cathode) Carbon Carbonelectrode electrode OH- Cu2+ Cl- H+ OH- Cu2+ Cl - H+ Copper (II) chloride solution, CuCl2
    • Positions of the ions in the electrochemical series Anode CathodeIons that are OH- , Cl- H+ , Cu2+ attracted OH- are preferred to be Cu2+are preferred to be discharged discharged (OH- is below Cl- in the ES) (Cu2+ is below H+ in the ES)Observation Bubbles of gas, O2 and Brown solid, Cu is formed Product is released 4OH- (aq) 2H2O (l) + O2 (g)Half equation Cu2+ (aq) + 2e- Cu (s) + 4 e-
    • Concentration of ions in electrolyte solutions Concentration of ions in electrolyte solution also can affects the choice of ions to be discharged An ion that is more concentrated is preferably discharged Anode – the ions to be discharged is determined by the concentration of ions Cathode – the ions to be discharged is determined by the position of the ion in the E.S
    • Concentration of ions in electrolyte solutions e- e- - e e- + (anode) - (cathode) Carbon Carbonelectrode electrode OH- Cu2+ Cl - H+ Concentrated copper (II) chloride solution, CuCl2
    • Concentration of ions in electrolyte solutions Anode CathodeIons that are OH- , Cl- H+ , Cu2+ attracted Cl- are preferred to be Cu2+are preferred to be discharged discharged (Cl- is more concentrated) (Cu2+ is below H+ in the ES)Observation Brown solid, Cu is formed Yellow bubbles gas, Cl2 and Product is releasedHalf equation 2Cl- (aq) Cl2 (g) + 2 e- Cu2+ (aq) + 2e- Cu (s)
    • Types of Electrodes e- e- - e e- + (anode) - (cathode)Silver plate Carbon electrode Ag+ Ag+ Ag Silver nitrate, AgNO3 solution
    • Types of Electrodes Anode Cathode Ions Ag atom releases one Ag+ receives one electron to electron to form Ag+ form metal atomsObservation and The silver plate corrodes Grey silver solid, Ag is Product formedHalf equation Ag (s) Ag+ (aq) + e- Ag+ (aq) + e- Ag (s)
    • Exercises Electrolysis of copper (II) sulphate, CuSO4, solution using carbon electrodes Anode Cathode Ions that are attracted Ion that are prefer to be discharged Observation Product Half equation
    • Exercises Electrolysis of concentrated potassium chloride, KCl, solution using carbon electrodes Anode Cathode Ions that are attracted Ion that are prefer to be discharged Observation Product Half equation
    • Exercises Electrolysis of nickel (II) sulphate, NiSO4, solution using nickel plate as anode and cathode Anode Cathode Half equation Observation Product
    • Factors that influence electrolysis of aqueous solutions POSITION OF IONS IN THE ELECTROCHEMICAL SERIES CONCENTRATION OF IONS IN THE ELECTROLYTE SOLUTION TYPES OF ELECTRODES
    • EXTRACTION OF METALS USES OF ELECTROLYSIS IN INDUSTRIESReacts with a carbonatemetal to form carbon OF PURIFICATION ELECTROPLATINGdioxide gas (CO2),water METALS OF METALS(H2O) and salt
    • Extraction of Metals Electrolysis can be used to extract metals from their ores Reactive metals that are more reactive than C such as (K, Na, Ca, Mg, Al) cannot be extracted through heating of their metal oxides with C They need to be extracted from their molten ores using the electrolysis process In this process: Electrolyte The molten ore Anode Carbon electrode Cathode Carbon electrode
    • Example: Extraction of aluminium from electrolysis of molten aluminium oxide, Al2O3
    • Purification of Metals Metals that have been extracted from their ores are normally not pure. They contains impurities which need to be removed These metals can be purified by electrolysis process In the purification process Electrolyte The solution that contains the metal ions Anode The impure metal plate Cathode The pure metal plate
    • Example: Purification of copper
    • Electroplating of Metals Many types of metals can be plated with other metals through electrolysis. The aim of metal plating through electrolysis includes:(i) making the metal more resistant to corrosion(ii) making the metal appear more attractive In the electroplating process Electrolyte The solution which contains ions of plating metal Anode Plating metal Cathode Metal to be plated
    • Example: Electroplating of a iron spoon with copper metal
    • ELECTROLYTIC CELL e- e- e- e- - (cathode) + (anode)Carbon Carbonelectrode electrode Copper (II) sulphate solution
    • VOLTAIC CELL e- e- V e- e- - (anode) + (cathode) Zn CuCopper (II)sulphate Zn (s) Zn2+ (aq) + 2e- Cu2+ (aq) + 2e- Cu (s)
    • VOLTAIC CELL Also known as galvanic cell Has two different metals which are immersed into an electrolyte and connected by wire Produces electrical energy from the chemical reactions occurring inside the cell Chemical energy electrical energy Example : Daniell cell
    • DANIELL CELL e- e- V e- e- Zn (-) Cu (+) (Anode) (Cathode) Dilute H2SO4 (Salt bridge)ZnSO4 solution CuSO4 solution Zn (s) Zn2+ (aq) + 2e- Cu2+ (aq) + 2e- Cu (s)
    • SALT BRIDGE Can be made from any electrolyte that does not react with the electrodes in Daniell Cell Function : (i) to allow the flow of the ions so the electric current is completed Example: (i) diluted H2SO4 (ii) sodium nitrate, NaNO3 solution (iii) Potassium chloride solution, KCl
    • DANIELL CELL e- e- V e- e- Zn (-) Cu (+) (Cathode) (Anode) CuSO4 solutionPorouspotcontainsZnSO4
    • Reactivity SeriesMETALS MORE ELECTROPOSITIVE K Na (negative terminal) Ca Mg Al Zn Fe Sn Pb MORE ELECTRONEGATIVE H Cu (positive terminal) Ag
    • Anode and Cathode  Anode – the electrode where the process of donation of electrons takes place  Cathode – the electrode where the process of receiving of electrons takes place ELECTROLYTIC CELL VOLTAIC CELLNegative terminal – Cathode Negative terminal – AnodePositive terminal - Anode Positive terminal - Cathode
    • ELECTROCHEMICAL SERIES
    • Electrochemical Series (pg.101) CATIONS ANIONS K+ F- Na+ Ca2+ SO42- Mg2+ NO3- Al 3+ Cl- Zn2+ Fe2+ Br- Sn2+ I- Pb2+ OH- H+ Tendency to Cu2+ discharge Ag+ increases
    • ELECTROCHEMICAL SERIES An arrangement of metals, based on thetendency of each metal atom to donate electrons
    • ELECTROCHEMICAL SERIES The higher the position of a metal in the electrochemical series:More electropositive The greater the tendency of the metal atoms to donate electrons
    • PRINCIPLES DURING CONSTRUCTING THE ELECTROCHEMICAL SERIESPotential differences Ability of a metal tobetween two metals in the displace another metalvoltaic cell from its salt solution
    • Potential differences between two metals in the voltaic cellWhen two different metals are immersed in an electrolytesolution, a potential difference is generated The value of the potential difference of a simple voltaic cell is affected by the position of the metals in the electrochemical series The further the two metals in the electrochemical series The larger the value of the cell voltage is produced
    • Potential differences between two metals in the voltaic cell The metal that is more electropositive Located higher in the Act as the negative terminal electrochemical series The metal that is less electropositiveLocated lower in the Act as the positive terminalelectrochemical series
    • Potential differences between two metals in the voltaic cell Mg Zn 3.0 V Pb 1.1 V 0.4 V Cu 0.5 V AgPredict the negative terminal, positive terminal and cell voltage of the following voltaic cell(b) Magnesium and silver (c) zinc and lead(c) Magnesium and zinc (d) zinc and silver
    • Metal DisplacementA metal that is more electropositive can displaceanother metal which is less electropositive fromits salt solutionA metal that is located higher in the electrochemicalseries can displace another metal which is locatedlower in the electrochemical series from its saltsolution This reaction – displacement reaction
    • Metal DisplacementExample: Zinc, Zn can displace copper, Cu, from copper (II) nitrate, Cu(NO3)2solution Zn (s) + Cu(NO3)2 (aq) Zn(NO3)2 (aq) + Cu (s) Metal displaced• Zn is more electropositive than copper• Zn can displace Cu from copper (II) nitrate, Cu(NO3)2 solution• The zinc, Zn, will dissolve and brown copper solid, Cu, will form
    • It can determined the terminals of voltaic cells IMPORTANCE OF THE ELECTROCHEMICAL SERIESReacts with a carbonate It can determined the It can predicted themetal voltage carbon cell to form for a pair of potential of a metal todioxide gasmetals (CO2),water displace another metal(H2O) and salt from its solution