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

=========================
NOTE THAT ^ MEANS Raise to
power.
Pls Draw Your Table As Usual And
Input The Following:-
Volume of pipette=25.00cm^3
indicator used- Methyl orange
colour change at end point-yellow
to orange/purple
Note Use Your School End Point.
Tabulate
=========================
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
================================
2a)
Tabulate
Test
(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
Test

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2bi)
Firstportionof
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
================================
3ai)
lime juice is acidic in nature and
the colour of methyl orange in
acidic medium is red
3aii)
Iron(iii)chloride will be reduced to
iro(ii) with yellow deposit of
sulphur
3iii)
The color of KM2O4 is decolorized
because SO2(g) acts as a reducing
agent.
3iv)
Addition of ethanoic acid to KCO3
results to the liberation of a
colorless and odorless gas CO2
which turns lime water milky
=========================
Completed.

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