Chemistary ppt by group b
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Chemistary ppt by group b

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    Chemistary ppt by group b Chemistary ppt by group b Presentation Transcript

    • b) Physical properties of non metals :-
    • 2) Chemical properties of metals :i) Reaction with oxygen :Metals react with oxygen to form metal oxides. When copper is heated it combines with oxygen to form copper oxide. 2Cu + O2 2CuO When aluminium is heated it combines with oxygen to form aluminium oxide. 4Al + 3O2 2Al2O3 Some metal oxides are basic oxides because they react with water to form bases. 4Na + O2 2Na2O Na2O + H2O 2NaOH K + O2 K 2O K2O + H2O 2KOH Some metal oxides show acidic and basic properties. They are called amphoteric oxides. Eg :- Aluminium oxide, Zinc oxide etc. Al2O3 + 6HCl 2AlCl3 + 3H2O (basic) Al2O3 + NaOH NaAlO2 + H2O (acidic) (Sodium aluminate)
    • The reactivity of different metals with oxygen is different :-
    • ii) Reaction with water :Metals react with water to form metal oxides or metal hydroxides and hydrogen. 2Na + 2H2O 2NaOH + H2 2K + H2O 2KOH + H2 Ca + H2O Ca(OH)2 + H2 2Al + 3H2O Al2O3 + H2 3Fe + 4H2O Fe2O3 + 4H2 The reactivity of different metals with water is different :- Sodium and potassium react violently with cold water to form sodium hydroxide and hydrogen and catches fire. - Calcium reacts less violently with water to form calcium hydroxide and water and does not catch fire. - Magnesium reacts only with hot water to form magnesium hydroxide and hydrogen. - Metals like aluminium, iron and zinc react only with steam to form the metal oxides and hydrogen. - Metals like lead, copper, silver and gold do not react with water.
    • iii) Reaction with acids :Metals react with dilute acids to form salts and hydrogen. Mg + 2HCl MgCl 2 + H2 2Al + 6 HCl 2AlCl 3 + 3H2 Zn + 2HCl ZnCl 2 + H2 Fe + 2HCl FeCl 2 + H2 The reactivity varies from metal to metal. For the above metals the decreasing order of reactivity is Mg > Al > Zn > Fe. Copper, silver and gold do not react with dilute HCl. Hydrogen gas is not evolved when metals react with nitric acid (HNO3) because it is a strong oxidising agent and it oxidises the H2 produced to water and is itself reduced to oxides of nitrogen. 3Cu + 8HNO3 3Cu(NO3)2 + 4H2O + 2NO2
    • iv) Reaction of metals with metal salt solutions :A more reactive metal displaces a less reactive metal from its salt solution. (Displacement reaction) Magnesium displaces copper from copper sulphate solution. Mg + CuSO4 MgSO4 + Cu Zinc displaces copper from copper sulphate solution. Zn + CuSO4 ZnSO4 + Cu Iron displaces copper from copper sulphate solution Fe + CuSO4 FeSO4 + Cu after 15 – 20 minutes
    • 3) Reactivity series of metals :-
    • 4) How do metals an non metals react ?
    • 5a) Formation of sodium chloride molecule – NaCl Na . AN = 11 EC = 2,8,1 + x xx + x Cl x xx Na xx x Cl .xx x x NaCl AN = 17 EC = 2,8,7 The atomic number of Na is 11, its electronic configuration is 2,8,1, it has 1 valence electron, it loses 1 electron to form Na + ion. The atomic number of Cl is 17, its electronic configuration is 2,8,7, it has 7 valence electrons, it gains 1 electron to form Cl - ion. Then the attraction between the Na + ion and Cl - ion results in the formation of sodium chloride molecule – NaCl.
    • b) Formation of Magnesium chloride molecule – MgCl2 Mg AN = 12 EC = 2,8,2 Cl + 1e AN = 17 EC = 2,8,7 . Mg. x + x Mg 2+ + 2e - 2,8 Cl - 2,8,8 xx Cl x x xx xx Cl xx x x 2+ Mg . Cl x xx xx . Cl x xx xx x x x x MgCl 2 The AN of Mg is 12, its EC is 2,8,2, it has 2 valence electrons, it loses 2 electrons to form Mg 2+ . The AN of Cl is 17, its EC is 2,8,7, it has 7 valence electrons, it gains 1 electron to form Cl -. Then the attraction between Mg 2+ ion and 2 Cl - ions results in the formation of Magnesium chloride molecule – MgCl .
    • 6) Ionic compounds (Electrovalent compounds) :Ionic compounds are compounds formed by the transfer of electrons from a metal to a non metal. Properties of ionic compounds :i) They are formed by the transfer of electrons and are made up of ions. i) They are crystalline solids. ii) They have high melting points and boiling points. iii) They are soluble in water but insoluble in organic solvents (like petrol, kerosene etc.) iv) They conduct electricity in molten state or in solution.
    • 7a) Occurence of metals :Some metals like gold, silver, platinum etc are found in the free state in the earth’s crust because they are least reactive. Most metals are found as oxides, carbonates, sulphides, halides etc. Minerals :- are elements or compounds which occur naturally inside the earth’s crust. Ore :- is a mineral from which metals can be extracted profitably. Gangue :- is the impurities present in the ore like rock particles, sand particles, clay particles etc. b) Extraction of metals from their ores :Metals are extracted from their ores in three main steps. They are :i) Concentration of the ore (Enrichment of the ore). ii) Reduction to the metal. iii) Refining (Purification of the metal). Concentration of the ore :- is the removal of gangue (impurities) from the ore by different methods.
    • 8) Steps involved in the extraction of metals from their ores :Ore Metals of high reactivity Metals of medium reactivity Electrolysis of molten ore Carbonate ore Pure metal Sulphide ore Calcination Roasting Metals of low reactivity Sulphide ore Roasting Oxide of metal Metal Reduction to metal Refining Refining
    • i) Extraction of metals low in the activity series :Metals which are low in the activity series can be reduced to the metals by heating in the presence of oxygen (Roasting). Eg :- Mercury is obtained from its ore Cinnabar (HgS) by heating in the presence of oxygen. When it is heated in the presence of oxygen it is first converted into mercuric oxide (HgO) and on further heating it is reduced to mercury. heat 2HgS + 3O2 2HgO + 2O 2 2HgO heat 2Hg + O 2 Copper is obtained from its sulphide ore (CuS) by heating in the presence of oxygen. heat heat 2CuS + 3O2 2Cu2O + 2SO2 2Cu2O + Cu2S 6Cu + SO 2
    • ii) Extraction of metals in the middle of the activity series : Metals in the middle of the activity series like Zn, Fe, Pb, are found as oxide, sulphide or carbonate ores. It is easier to obtain metals from their oxides than from their sulphides or carbonates. So non oxide ores are converted into oxide form before reduction. Non oxide ores can be converted into oxide form by roasting or calcination. Roasting :- is heating of an ore in the presence of oxygen. It is used to convert suphide ores into oxide form. Eg :- 2 ZnS + 3O2 heat 2 ZnO + 2SO2 Calcination :- is heating of an ore in the absence of oxygen. It is used to convert sulphide ores into oxide form. heat Eg :- ZnCO3 ZnO + CO2 The oxide ore is then reduced to the metal by heating with a reducing agent. The most common reducing agent is coke (carbon). heat Eg :- ZnO + C Zn + CO
    • Thermit reactions :-
    • GENERAL
    • iii) Extraction of metals at the top of the activity series :Metals at the top of the activity series like K, Na, Ca, Al etc. cannot be obtained from their ores by simple heating or by heating with reducing agents. They are obtained by electrolytic reduction of their molten chlorides. Eg :- When electric current is passed through molten sodium chloride, sodium metal is deposited at the cathode and chlorine gas is deposited at the anode. At cathode :- Na + + e At anode :- 2Cl - Na (Sodium metal) Cl2 + 2e - (Chlorine gas)
    • 9) Refining of metals :The removal of impurities from the metal to obtain the pure metal is called refining of metals. The most common method for refining of metals is electrolytic refining. In this method a block of the impure metal is made the anode and a thin sheet of the pure metal is made the cathode. The electrolyte is a salt solution of the metal to be purified. Eg :- In the electrolytic refining of copper, a block of impure copper is made the anode and a thin sheet of pure copper is made the cathode. The electrolyte is acidified copper sulphate solution. When electric current is passed through the electrolyte, pure copper from the anode is deposited at the cathode and the impurities settle down as anode mud.
    • 10a) Corrosion :Corrosion is the damage caused to metals due to the reaction of metals with oxygen, moisture, carbon dioxide etc. Eg :- Formation of brown coating of rust over iron. Formation of green coating of basic copper carbonate over copper. Formation of black coating of silver sulphide over silver. To show that air and moisture are necessary for the rusting of iron :Take three test tubes marked 1,2,3 and put iron nails in each of them. Put some anhydrous calcium chloride in test tube 1 to absorb moisture. Pour some boiled distilled water in test tube 2 and pour some oil over it to prevent air into the test tube. Pour some water in test tube 3. Cork the test tubes and leave them for a few days. The nails in test tube 1 does not get rusted because it had only air and no water. The nails in test tube 2 does not rust because it had only water and no air. The nails in test tube 3 gets rusted because it had air and water.
    • b) Prevention of corrosion :Corrosion of metals can be prevented by :i) Applying oil or grease. ii) Applying paint. iii) By galvanisation. (Coating with zinc) iv) By tinning. (Coating with tin) v) By electroplating. (Coating a less reactive metal like chromium) vi) By alloying. (Making alloys) c) Alloy :An alloy is a homogeneous mixture of a metal with other metals or non metal. Eg :- Steel – iron, carbon Stainless steel – iron, carbon, cobalt, nickel Brass – copper, zinc Bronze – copper, tin Solder – Lead, tin (used for welding electrical wires together) If one of the metals in an alloy is mercury, it is called an amalgam.