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WAEC GCE 2017 Chemistry Practical Solutions Answer – Nov/Dec 2017 Expo

WAEC GCE Chemistry Practical Questions and Answer Solutions – NOV/DEC 2017 Expo Runz.


2a)
TEST|OBSERVATION|INFERENCE
2ai)
TEST: A+distilled water and stirred
OBSERVATION: A disolved in water
INFERENCE: A is soluble in salt
2aii)
TEST: A(aq)+litmus paper
OBSERVATION: Turns blue litmus paper red
INFERENCE: A is an acidiic salt
2aiii)
TEST: A(aq)+NaOH(aq)- in drops, then in excess
OBSERVATION:
-White gelatinous ppt formed.
-Precipitate soluble/dissolved
INFERENCE:
Pb^2+ or Zn^2+ or Al^3+ present
Pb^2+ or Zn^2+ or Al^3+ present
2aiv)
TEST:
A(aq)+NH3(aq)
- in dropss,
- then in excess
OBSERVATION:
-White gelatinous precipitate
-Precipitate insoluble
INFERENCE:
-Pb^2+ or Zn^2+ or Al^3+
-Al^3+ present
2av)
TEST:
A(aq)+FeSO4(aq)+conc H2SO4
OBSERVATION:
Brown ring forms between the two solutions
INFERENCE:
NO3- confirmed

2bi)
A is aluminium trioxonitrate(v)
2bii)
Al(NO3)3

2c)
TEST|OBSERVATION|INFERENCE
2ci)
TEST:
K+NaHCO3(aq)
OBSERVATION:
No visible reaction is observed
INFERENCE:
NaHCO3(aq) does not show result for alkanols(K)
2cii)
TEST: K+benedict solution+heat
OBSERVATION: There is no change in the colour of the benedicts solution
INFERENCE: Benedicts solution is not an indicator for alkanols(K)
2ciii)
TEST:
K+KMnO4(aq)
OBSERVATION:
KMnO4(aq) solution changes from purple to colourless
INFERENCE:
Alkanol is being oxidized by KMnO4
2civ)
TEST: K+CH3COOH+conc H2SO4
OBSERVATION: pleasant fruity smell is observed
INFERENCE: Esterification reaction has occured


3a)
i) Putsome distilled water in a beaker
ii) Measure 100cm^3 of 2.00mol/dm^3 of the stock solution by means of a burette and pour all the solution into the beaker containing the distilled water
iii) Stir the solution
iv) Transfer the solution into a 250cm^3 volumetric flask by means of a funnel
v) Ensure that all the solution in the volumetric flask has been transferred by thoroughly rinsing the inside of the beaker with distilled water
vi) Dilute the solution in the volumetric flask with distilled water until it reaches the 250cm^3 mark
vii) Shake the solution carefully

3b)
i) CH3COONa: It forms basic solution
ii) Al2(SO4)3: Acidic solution
iii) KNO3: Neutral solution

3c)
Acidified potasium tetraoxomanganate(vii) KMnO4 was placed in the burette
 
1ai)
tabulate
Burette reading 1cm^3|1|2|3|
final reading|33.10|30.00|25.0O|
initial reading|9.60|7.50|2.40|
volume of acid used 1cm^3|23.50|22.50|22.60|
1aii)
avaerage volume of acide used= 22.50+22.60/2 =22.55cm^3

1bi)
5Fe^2+ +Mn0^-4 + 8H^+ ---->5Fe^2+ +Mn^2+ + 4H20
MA=?
MB=0.0200moldm^-3
VB=22.55cm^3
VA=25cn^3
NA=5
NB=1
MAVA/MBVB=NA/NB
MA*25/0.0200*22.55=5/1
MA=0.0200*22.55*5/25
=0.0900moldm^-3

1bii)
Molar mass of FeSO4' 7H2O
56+32+(4*16)+7(18)
56+32+64+126
=278gmol^-1
Con of FeSO4 7H2O in gdm^-3=0.0900*278=25.02gdm^-3
1biii)
Mass of =33.60-25.02
FeSO4 7H2O=8.58gdm^-3
%age of FeSO4 7H20=8.58/33.60*100=25.54%

1ci)
The reason is KMno4 is a very strong oxidizing agent which can oxidise hydrochloric acid
1cii)
Because of the dark purple color of KMnO4 the bottom of the minisucs in the burette is not clearly seen so the upper of the miniscus is read
1ciii)
Because the product Mn^2+ formed is colourless
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