[WAEC EXPO 2017] CHEMISTRY PRACTICAL QUESTIONS AND ANSWERS POSTED HERE


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1bii)
Molar mass of Bing mol-1:
Molar mass of Na2CO3.yH2O=mass concentration of Bingdm-3
molar concentration of Binmoldm-3
=13.6gdm-3
0.0475moldm-3
=286gmol-1
1biii)
Molar mass of Na2CO3 =[(2×23)+12+(16×3)]=106gmol-1
Mass of anhydrous Na2CO3=106×0.0475gdm-3
=5.035gdm-3
Mass of water=13.6-5.035gdm-3
=8.565gdm-3
Mass of Na2CO3 =Molar mass of Na2CO3
Mass of water y×Molar mass of water
5.035=106
8.565 18y
y =106×8.565
5.035×18
=10
(2)Tabulate
Test
(a)(i)Fn+H2O,then
filter
Observation
White residue and blue
filtrate was observed
Inference
Fn is a mixture of
soluble and insoluble
salts
Test
(ii)Filtrate+NaOH(aq)in
drops,then in excess
Observation
A blue gelatinous
precipitate which is
insoluble in excess
NaOH(aq)was formed
Inference
Cu2+present
Test
(iii)Filtrate+NH3(aq)in
drops,then in excess
Observation
A pale blue gelatinous
precipitate was
formed. The precipitate
dissolves or is soluble
in excess NH3(aq)to give
a deep blue solution
Inference
Cu2+confirmed
Test
(iv)Filtrate+dil.HNO3
+AgNO3(aq)
Observation
No visible reaction
White precipitate
formed
Inference
Cl-present
Test
+NH3(aq)in excess
Observation
Precipitatedissolvedin
excessNH3(aq)
Inference
 
 
 
 

Cl-confirmed



(3)
(i ) P is delivery tube
Q is drying tower
R is quick lime
S is dry ammonia
T is retort stand
(ii)By upward delivery
(iii)It serves as a drying agent
(iv)Ca(OH)2(s)+2NH4(s)-
>CaCl2+2H2O(l)+2NH3(g)


 2bi)First portion of residue +NaOH(aq) in drops, then in excess
Observation
White powdery precipitate which is insoluble in excess NaOH(aq)
Inference
Ca2+ present
Test
2bii)Second portion of residue + dil.HCl
Observation
Effervescence/bubbles; colourless, odourless gas evolved.
Gas turns lime water milky and turns damp blue litmus paper red.
Inference
Gas is CO2
CO3^2- or HCO3- present
===============
3i) Lime juice is cacitic in nature and the color of methyl orange in active medium is Red 


3ii) Iron(iii)chloride will be reduced to iron(ii) with the yellow deposit of Sulphur




3iv)Addition of ethanoic acid to k2lo3 results to the liberation of a colourless or odourless gas co2 Which turns lime water milky
3c. Sulfur dioxide gas (SO2) is bubbled through a solution of acidified potassium permanganate (KMnO4). An oxidation-reduction reaction occurs.
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