Waec 2017 Chemistry (Practical Alternative A) Answers – May/June Expo

Waec 2017 Chemistry (Practical Alternative A) Answers – May/June Expo

NOTE:
Tita means θ
^ means Raise to power
Pie means π
/ (means) division or divide
2 whole no 3/4 means 2¾
* means
multiplication (×)
Sqr root means √
Proportional means ∝

1)
Tabulate
Burette reading|Final burette reading
(cm^3)|Initial burette reading (cm^3)|
Volume of acid used(cm^3)|
Rough- 24.10,0.00,24.10
First- 23.80, 0.00, 23.80
Second- 23.75, 0.00, 23.70
Third- 23.75, 0.00, 23.75
Average volume of A used = 23.80 + 23.70 + 23.75cm^3/3 =23.75cm^3

1bi)
CAVA/CcVc=2/1
Cc=CAVA/2VC
=0.100*23.75Moldm^-3/2*25.00
=0.0475moldm^-3
amount of A used = 0.100x
VA/1000=0.100*23.75/1000 =0.00237
2moles Of A = 1mole of C
0.002375mol of A = 0.002375mol/2
100cm^3 of C contain 0.00237*100mol/2*25 =0
1000cm3ofCcontained0.002375x1000mol 2×25 =0.0475mol
concentration of C in moldm-3 =0.0475moldm-3

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

More Typing[Keep Refreshing]
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(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

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

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