Waec

2018/19 Waec Chemistry Practical Questions And Answers (May/June Exam)

2018 Waec Practical Agric Answers

2018 WAEC CHEMISTRY PRACTICAL ANSWERS

Use Your School End Point.
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)
TEST: C + about 5cm3 of distilled water
OBSERVATION: C dissolves to form a clear solution;
Turns blue litmus paper to pink
INFERENCE: C is a soluble salt;
C is fairly acidic

(2ai)
TEST: 1st portion of C + NaOH(aq) in drops;
then excess
OBSERVATION: pale-blue precipitate forms in drops of NaOH(aq) which persists in excess of NaoH(aq)
INFERENCE: cu²+ present.

(2aii)
TEST: 2nd portion of C + NH3(aq) in drops and then in excess
OBSERVATION: pale blue precipitate forms in drops of NH3(aq).
Ppt dissolves to form a deep blue coloration.
INFERENCE: Cu²+ present.
Cu²+ confirmed

(2aiii)
TEST: 3rd portion of c + AgNO3(aq) + HCL(aq)
OBSERVATION: a creamy white ppt forms.
INFERENCE: Halogen/Halides present.

(2bi)
TEST: D + about 5cm³ of distilled H2O
OBSERVATION: D dissolves to form a clear solution.
The test tube feels warmth
INFERENCE: D is a soluble salt.

(2bii)
TEST: 2cm³ of D + HCL(aq)
OBSERVATION: effervescence occurs, an odourless and colourless gas evolved. Precipitate dissolves in dil HCL(aq)
INFERENCE: CO32-, so32-present
CO32- 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)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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