WAEC 2018 CHEMISTRY PRACTICAL ANSWER EXPO

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WAEC 2018 CHEMISTRY PRACTICAL ANSWERS

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)

Con in mol/dm3=conc in g/dm^3/molar mass

con of B in g/dm^3 =4.80/0.25 =19.2g/dm^3

molar mass = Fe+2Cl = 56+2(35.5)=127g/mol

conc in mol/dm^3 =19.2/127 =0.15mol/dm^3

1bii)

using CAVA/CBVB = NA/NB

CA*11.80/0.15*20=1/5

CA=0.15*20*1/11.80*5

CA=0.05moldm^-3

1biii)

mole =con(mol/dm^3)x vol (dm^3)

=0.15*20/1000

=0.003moles.

2a)

-Observation-

part of the C dissolves,colourless filtrate salt

-Inference-

C is a mixture of soluble salt

2bi)

-observation-

white precipitate formed

-Inference-

Cl is present

2bii)

-Observation-

precipitate dissolves

-Inference-

Cl confirmed

2biii)

-Observation-

colourless gas evolved with characteristic choking smell, turns litimus paper blue

-Inference-

Gas is NH3

2c)

-Observation-

Residue dissolves liberating a colourless gas which turns lime water milky

-Inference-

gas is CO2

CO^2-3 present

3a)A white precipitate of barium sulphate will be formed by the instant reaction between barium chloride and sulphuric acid.

BaCl2 + H2SO4 = BaSO4 + 2HCl

3b)Iron sulfide reacts with hydrochloric acid, releasing the malodorous (rotten egg smell) and very toxic gas,hydrogen sulphide. FeS + 2 HCl → FeCl2+ H2S

3c)When solid iron filings are added to dilute aqueous Hydrochloric acid, Iron (II)chloride or ferrous chloride is formed , with the liberation of Hydrogen gas.

Fe (s) + 2HCl (aq) ……..> FeCl2(aq) + H2 (g)

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