WAEC Chemistry Answers

1-10: DAAABDADCA
11-20: BABBBDCCAC
21-30: CDABDDACBC
31-40: BBDCCCCDBA
41-50: DCABADBABB 
(1ai) Ionic bond is the bond that exists between metallic and non-metallic atoms. 
(1aii) I ionic bond, II ionic and covalent bond +1y2+2x-2*3=0 
(1bi) Na2S2O3, 2+2x-6=0 2x=6-2 X=4/2=2  :. the oxidation number of sulphur in Na2S2O3 is 2 
(1c) Faraday’s first law states that the quantity of substance deposited or liberated during electrolysis is directly proportional to the amount of current passing through the electrolyte at constant temperature an pressure at a given time i.e Q=it 
(1d) i. SO3 ii.NaO 
(1e) i. Exothermic ii. Endothermic 
(1f) i. It turns blue litmus paper red ii. It turns red litmus to red 
(1g)Efflorescence are substances when exposed to the atmosphere, they lose their water of crystalization to the atmosphere. 
(1h) (i.) It is used in making typewriter ribbon (ii.) for making shoe polish (iii.) For making carbon black  (1i) i. It is used for hardening of oil ii. It is used in breaking heavy hydrocarbon light fraction iii. It is used in producing esters for making soap 
(1j) Recall, m= MQ/nF, where m= mass of sliver deposited. Ag^+ + e^- –> Ag n=1, m/M=No of moles = 10920/1*96500 m/M=No of moles = 0.113 moles. ==================== PLS NOTE THAT ^ MEANS RAISE TO POWER. ==================== 
(2ai) This can be defined as a substance formed when an element gains or looses election  (2aii) Isotopes: these are element that exist with the same at its first election, in the valence shell while aluminium while aluminium retains two hence magnesium will become more stable than aluminium. 
(2bi) (I) 12Mg= 1S^22S^22p^63S^2 13AL= 1S^22S^22P^63S^23P^1 
(II) This is because the first ionization energy increases across the period but decreases down the group 
(2bii) Na2O,MgO, Al2O3 
(2c) (1) Allotropes are atoms that exist in different forms but have the same physical state (ii)Diamond and Graphite (iii) -Diamond is used for making jeweleries - Graphite is used for making lead pencil 
(2d) 2Nacl+H2SO4 –> Na2SO4+2Hcl  (i) -The gas turns blue litmus paper to red -The gas is colourless  (ii)2Nacl+H2SO4–> Na2SO4+2Hcl 
(2e) Molar mass(gmol^-1)=mass/Amount. Amount in moles= 5.68*10^-3/28. Amount in moles=2.03*10^-4moles. Amount in moles=0.000203moles. 
(3ai) coagulation sedimentation filteration disinfection 
(3aii.) magnesium ion and calcium ion 
(3aiii) -it wastes soaps - it causes furring of kettles and boilers 
(3aiv) -crude oil spillage refuse and sewage 
(3bi) water is a polar solvent which is an excellent solvent for electrovalent substances like NaCl but oil is non-polar which has little affinity for hydroxyl ion 
(3bii) -as dehydrating agent -as an acid -as oxidizing agent 
(3ci) oxygen and hydrogen chloride 
(3cii.) I-NaOH II- because it is soluble in water. 
(4ai) I. Anode is the positive electrode through which current enters the electrolyte II. Cathode is te negative electrode through which current leaves the electrolyte 
(4aii) I. Nacl–> Na+ Cl- II. Alcl3–> Al^3+ cl- Al2O3–>Al^3+ O2- 
(4aiii) This is because the reaction of sodium with water is very explosive and violent but that of aluminum is not 
(4bi) This is because one substance is undergoing oxidation and another reduction at the same time. 
(4bii) Cr2O7^-5 –> Cr^+2 Cl- –> Cl2. 
(4c) Current(I)=6A Time(t)=1hr30mins = (1*3600)+(30*60) =3600+1800 =5400s Quantity of Electricity(Q) =I*t =6*5400 =32400coulombus m=MQ/nF Al^3+ + 3e^- –> AL n=3 m= 27*32400/3*96500 m=3.02g Mass of aluminum deposited is 3.02g