Tuesday, April 11, 2017

WASSCE 2017/18 Chemistry Practicals Solutions [White Paper Quantitative Analysis]

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One Of Our Teachers has decided to solve the WASSCE Chemistry Practicals Schedule to hold on11th April, 2017 based on the White Paper Released.

Candidates are to study the solving as 70% of are confirmed and will be among the questions for the exam.

The Chemistry Practicals Solutions are in Image Format, so click on them to download or view.
(1a)
Pls 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
2x25=0.0475mol
concentration of C in moldm-3 =0.0475mol/dm^3

(1bii)
C contains 14.3g in 500cm3
.:. Conc of c in gdm^-3 is 28.6dm^-3.

(1biii)
Molar mass of Bing mol-1:
Molar mass of Na2CO3.yH2O=mass concentration of B in g/dm^3
molar concentration of B in mol/dm3=13.6gdm-3
0.0475mol/dm3=286gmol^-1

(1biv)
The hydrated salt is NA2CO3.XHO=286
2(23)+12+3(16)+X(2+16)=286
46+60+18X=286
18X+106=286
18X=286-106
X=180/18
X=10
The number of water molecules in the hydrated salt is 10

==================================
Pls Tabulate:
(2ai)
TEST: F + water
OBSERVATION: Partially soluble salt
Inference: F is a mixture of soluble and insoluble salts

(2bi)
TEST: Filtrate + NaOH(aq)in drops,then in excess
OBSERVATION: A pale blue gelatinous precipitate which is insoluble in excess NaOH(aq).
INFERENCE: Cu2+ present

(2bii)
TEST: Filtrate + NH3(aq) in drops,then in excess.
OBSERVATION: A pale blue precipitate was formed. The precipitate is soluble in excess NH3(aq)to give a deep blue solution.
INFERENCE: Cu2+ confirmed

(2c)
TEST: Filtrate + dilute HNO3(aq) + AgNO3(aq)
OBSERVATION: White precipitate formed which turns grey on exposure to light.
INFERENCE: Cl- present

(2di)
TEST: Residue + HNO3(aq)
OBSERVATION: Effervescence of a colourless, odourless gas which turns moist blue litmus paper faint and turns lime water milky.
INFERENCE: CO2(g) from CO3^2- or HCO3- present

(2dii)
TEST: Residue + NaOH(aq)
OBSERVATION: White powdry ppt insoluble in NaOH(aq)
INFERENCE: Ca2+ present.


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(3i)
The colour of methyl orange will change from orange to yellow

(3ii)
Iron(III)chloride will be reduced from brown iron to green iron
Fe^3+(aq)->Fe^2+(aq)

(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




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