Chemistry Practical Waec 2017 Free Expo Answers

Chemistry Practical Waec 2017 Free Expo Answers

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Tuesday, 11th April, 2017
Chemistry 3 (Practical) (Alternative A) 09.30am – 11.30am (1st Set)

Chemistry 3 (Practical) (Alternative A) 12.00pm – 2.00pm (2nd Set)
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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


1b 

CaVa Na 
_____ =____
CcVc Nc

CaVa 1
______ = ___
CcVc 2
Cc= CaVa
_____
2Vc 

= 0.100 × 23.75 mol dm^3
________________
2 × 25.00
= 0.0475 mol dm^3

Conc. Of C in mol dm^-3 = 0.0475


(a)(i)Fn+H2O,then
filter



White residue and blue
filtrate was observed


Fn is a mixture of
soluble and insoluble
salts

(ii)Filtrate+NaOH(aq)in
drops,then in excess


A Blue gelatinous
precipitate which is
insoluble in excess


NaOH(aq)was formed
Cu2+present

(iii)Filtrate+NH3(aq)in
drops,then in excess


A pale blue gelatinous
precipitate was
formed.The precipitate
dissolves or is soluble
in excess NH3(aq)to give
a deep blue solution


Cu2+confirmed

(iv)Filtrate+dil.HNO3
+AgNO3(aq)
+NH3(aq)in excess
No Visible Reaction
White Precipitate
formed
Precipitate dissolved in
excess NH3(aq)


Cl-present
Cl-confirmed
(b)(i)First Portion Of
residue+NaOH(aq)in
drops,then in excess
White Powdery
precipitate which is
insoluble in excess
NaOH(aq)


Ca2+present
(ii)Second Portion Of
residue+dil.HCl


Effervescence/bubbles;
colourless,odourless
gas evolved.Gasturns
lime water milky and
turns damp blue litmus
paper red.


GasisCO2
CO3
2-orHCO3
-present


(a)(i)+H2O,then
filter



White residue and blue
filtrate was observed


Fn is a mixture of
soluble and insoluble
salts

(ii)Filtrate+NaOH(aq)in
drops,then in excess


A Blue gelatinous
precipitate which is
insoluble in excess


NaOH(aq)was formed
Cu2+present

(iii)Filtrate+NH3(aq)in
drops,then in excess


A pale blue gelatinous
precipitate was
formed.The precipitate
dissolves or is soluble
in excess NH3(aq)to give
a deep blue solution


Cu2+confirmed

(iv)Filtrate+dil.HNO3
+AgNO3(aq)
+NH3(aq)in excess
No Visible Reaction
White Precipitate
formed
Precipitate dissolved in
excess NH3(aq)


Cl-present
Cl-confirmed
(b)(i)First Portion Of
residue+NaOH(aq)in
drops,then in excess
White Powdery
precipitate which is
insoluble in excess
NaOH(aq)


Ca2+present
(ii)Second Portion Of
residue+dil.HCl


Effervescence/bubbles;
colourless,odourless
gas evolved.Gasturns
lime water milky and
turns damp blue litmus
paper red.


GasisCO2
CO3
2-orHCO3
-present

(2a)(i)Fn+H2O,then
filter



White residue and blue
filtrate was observed


Fn is a mixture of
soluble and insoluble
salts

(2b)Filtrate+NaOH(aq)in
drops,then in excess


A Blue gelatinous
precipitate which is
insoluble in excess


NaOH(aq)was formed
Cu2+present

(2bii)Filtrate+NH3(aq)in
drops,then in excess


A pale blue gelatinous
precipitate was
formed.The precipitate
dissolves or is soluble
in excess NH3(aq)to give
a deep blue solution


Cu2+confirmed

(2c)Filtrate+dil.HNO3
+AgNO3(aq)
+NH3(aq)in excess
No Visible Reaction
White Precipitate
formed
Precipitate dissolved in
excess NH3(aq)


Cl-present
Cl-confirmed

(2di)(i)First Portion Of
residue+NaOH(aq)in
drops,then in excess
White Powdery
precipitate which is
insoluble in excess
NaOH(aq)


Ca2+present

(2dii)Second Portion Of
residue+dil.HCl


Effervescence/bubbles;
colourless,odourless
gas evolved.Gasturns
lime water milky and
turns damp blue litmus
paper red.


GasisCO2
CO3
2-orHCO3
-present


3i)Lime Juice is acidic in Nature and the colour of methyl orange in acidic medium is red

3ii)Iron(II)Chloride will be reduced to Iron(II) with the yellow deposit of sulphur

3c. Sulfur dioxide gas (SO2) is bubbled through a solution of acidified potassium permanganate (KMnO4). An oxidation-reduction reaction occurs.

Potassium permanganate has a purple colour. Sulphur dioxide is a reducing agent. Potassium permanganate is an oxidizing agent. When sulphur dioxide reacts with potassium permanganate the solution decolourizes. Color changes from Purple to colorless

3iv)Addition of ethanoic acid to k2lo3 results to the liberation of a colourless or odourless gas co2 Which turns lime water milky