WAEC GCE CHEMISTRY ANSWERS 2 & 8 (2ai) Graham's law of diffusion states that the rate of diffusion of gas at constant temperature and pressure is inversely proportional to the square root of its vapour density. (2aii) (I) PB = 1.013*10^5Nm^-3 VB = 5dm^3 Pc= 3.039* 10^5Nm^-2 Vc= 5dm^3 PT= PB+PC PT = 1.013*10^5+3.03*10^5 PT= 4.052*10^5Nm^-2 (II) PT:(1.013*10^5*10) + (3.03*10^5*10) PT= 4.052*10^6Nm^-2 (2bi) No of mole of methane = 0.50mol, No of mole of oxygen= 1.5mol, 1mol of methane produces 2 mol of oxygen, 0.50mol of methane produces 2/1 * (0.50) = 1.0 mol of oxygen Methane is in excess of oxygen (2bii) 2mol of oxygen produces 2moles of steam, 1.5mol of oxygen produces 2/2*(1.5) = 1.5moles of steam (2biii) 3.0 = no of molecules/ 6.02*10^23 no of molecules = 3.0*6.02*10^23 = 18.06 * 10^23 particles =1.806*10^24 (2c) To 1cm^3 of unknown substance, add calcium hydroxide. The presence if milky solution confirms the presence of carbon(iv)oxide (2di) (I) By using calcium Chloride (II) Dry agent (2dii) Because it is less denser than air (2diii) Hydrogen perioxide and Cu are formed (8a) - Rain -Spring -Well (8b) i. Alum is added to cause coagulation of particles ii. To allow for the passage of carbon(iv)oxide iii. To kill germs (8c) i. Sodium hydroxide and hydrogen gas are produced ii. Water produces colourless solution with copper (II)tetraoxosulphate(iv) (8di) (I) paint (II) Oil (8dii) - Erosion - Acid rain (8diii) (I) Furing of kettles and boilers stalagmites and stalactites (II) To remove the hardness in water (8e) Al + H2SO4 -> Al2O3 + SO2 + H2 No of moles of SO2 = 1120/22400 =0.05 0.05 = mass/molar mass Molar mass of SO2 = 32+(16*2) = 64g/mol 0.05 = mass/64 mass= 0.05 * 64 = 3.2g 3.2g of SO2 produces 2.50g of Al 1g of SO2 produces 2.50g/3.2 of Al = 2.50/3.2*(27) = 21.09g. Pure aluminium = 21.09 - 2.50 = 18.59g
Posted on: Mon, 23 Sep 2013 15:09:57 +0000
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