link [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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