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2021 GCE:HOW TO GET WAEC GCE QUESTION AND ANSWER BEFORE EXAM START

 
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WAEC Chemistry Practical Answer – 2020 Expo

WAEC 2020 Chemistry Practical Expo Answer
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2020 WAEC-CHEMISTRY-PRACTICAL ANSWERS 

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(1a) 
In a tabular form
Burette Reading|1st reading|2nd reading|3rd reading
Final |15.25|0.00|45.79|
Initial|0.00||15.25|30.53|
Volume of acid used |15.25|15.28|15.26
Average volume of acid used = 15.25 + 15.26/2
= 15.255cm³
=15.26cm³
(1bi) 
Given: Mass of conc of A = 5g/500cm³ = 5g/0.5dm³
Ca = 10g/dm³
A is HNO3
Therefore; Molar mass = 1+14+(16×3)
= 15+48
=63g/mol
Molarity of A = gram conc/molar mass
Ca = 10/63 = 0.1587mol/dm³
(1bii) 
Using CaVa/CbVb = nA/nB
With reacting equation:  
HNO3 +NaOH–>NaNO3 + H2O
nA = 1, nB = 1
0.1587×15.26/Cb×25.00 = 1/1
25Cb = 0.1587×15.26
CB = 0.1587×15.26/25
CB = 0.09687mol/dm³
(1biii)
B is NaOH
Molar mass = 23+16+1
=40g/mol
Conc of B in g/dm³ = molarity×molar mass
=0.09687×40
=3.8748g/dm³
(1biv) 
No of moles present in 250cm³ of NaOH is 
= molar conc. × volume 
= 0.09687 × 250/1000
= 0.0242 moles 
Mole ratio of NaOH and NaNO3 is 1:1
No of moles of NaNO3 which reacted is 0.0242
Mass of NaNO3 formed = molar mass × no of moles 
= 85 × 0.0242
=2.057grams
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(2a) 
TEST
C + burning splint 
OBSERVATION 
Sample C bursts into flame
It burns with non-smoking blue flame, without soot. 
Colourless gas that turns wet with blue litmus paper faint red and turns lime water milky is present 
INFERENCE 
C is volatile and flammable. The gas is CO2 from combustion of a saturated organic compound. 
(2bi) 
TEST
C + distilled water + Shake 
OBSERVATION 
Clear or colourless solution is observed 
INFERENCE 
C is miscible with water
(2bii) 
TEST
C + Acidified K2Cr2O7
OBSERVATION 
Orange color of K2Cr2O7 Solution turns pale green and eventually pale blue on cooling 
INFERENCE 
C is a reducing agent
(2c) 
TEST
D + C + 10% NaOH + Shake
OBSERVATION 
D dissolve slowly in C and produces reddish brown solution 
Reddish brown solution turns yellow precipitate. The precipitate has an antiseptic odour
INFERENCE 
D is soluble in organic solvents 
Ethanol, ethanal or a secondary alkanol is present 
(2d) 
Compound belongs to the class of secondary alkanol
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(3ai)
Zinc nitrate
(3aii)
2 Zn(NO 3 )2 —–>2 ZnO + 4 NO 2 + O 2
(3aiii)
It turns white when cold from it yellow colour when it was hot
(3b)
Pipette / measure 50.0cm3 of the stock solution into a 250
cm3 volumetric flask (containing some distilled water). Shake / swirl and add more distilled water until the mark is reached.
(3c)
Al2(SO4)3 – turns blue litmus red
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Completed!!!!!!!
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