WAEC 2016 CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS NOW AVAILABLE FOR FREE

Wednesday 13th April 2016 CHEMISTRY PRACTICAL ALT. A 9.30AM � 11.30AM (1) TABULATE: Volume of pipette Burette reading(cm3)|Rough titre(cm3)|1st titre(cm3)|2nd titre(cm3) Final reading(cm3) |20.00|19.60|19.60 Initial reading(cm3)|0.00 |0.00 |0.00 Volume of acid used |20.00|19.60|19.60 Average titre=(19.60+19.60)/2 cm3 =39.20/2 cm3 =19.60cm3 Equation=>2MnO4^-+5C2O4^2-+16H^+->2NA^2++8H2O+10CO2 (1bi) Conc of B in mol/dm3 CaVa/CbVb=Na/Nb (0.05*19.6)/(Cb*25.0)=5/2 5*Cb*25=2*0.05*19.6 Cb=(2*0.05*19.6)/(5*25)=1.96 Cb=0.0157mol/dm3 Cb=0.016mol/dm3 (1bii) Conc in B in g/dm3 =0.0157*158 =2.4806g/dm3 =2.481g/dm3 (2a ) Observation: C dissolved partially in solution Inference:Salt C in a mixture of soluble and insoluble (2b)Observation:White precipitate is formed.White precipitate dissolved in excess of NH3(aq), Inference:Cl^- is present.Cl^- is confirmed (2ci) Observation: Effervescence occur with liberation colourless odourless gas which turn lime water milky Inference: CO2(g) from HCO3^- or CO3^2- (2cii) Observation:White precipitate is formed which is soluble in excess, Inference: Pb^2+,Zn^2+,Al^3+ may be present (2ciii) Observation:white precipitate is formed which is soluble in excess, Inference:Zn^2+ (3a) (i)Simple distillation-wide boiling point difference between constituent liquid (ii)Chromatography-Relative migration of constituents of mixture over an absorbent or rf-value difference of constituents of mixture (iii)Fractional distillation-Close boiling point between constituent liquid (3b) (i)For easy identification of the end point ie the point of complete titration where the colour change is observed