WAEC Expo 2018 Chemistry 3 Practical (Alternative A) Answers And Questions - WobeGist Online

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Tuesday, 3 April 2018

WAEC Expo 2018 Chemistry 3 Practical (Alternative A) Answers And Questions





Please Use Your School End Point.
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1a)
Volume of pepette = 25.00Cm^2
Indicator Used = Methyl Orange
Tabulate
BURETTE READING|ROUGH|1ST|2ND|3RD|
Final reading Cm^3|25.00|34.00|29.20|24.10|
Initial Reading Cm^3|0.00|10.00|5.00|0.00|
Volume Of Acid Used In Cm^3|25.00|24.00|24.20|24.10|
Average Volume of Acid used =(24.00+24.20+24.10/3)cm^3
=24.10cm^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.
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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
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3i)
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)
The iron dissolves, releasing hydrogen and making an iron chloride solution:
Fe + 2HCl → FeCl₂ + H₂
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