NECO GCE 2021 CHEMISTRY PRACTICAL ANSWERS-NOV/DEC EXPO

Wednesday, 1st December 2021

Chemistry Paper I (Alternative to Practical)
2.00 pm – 4.00 pm

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(1ai)
Methyl orange

(1aii)
The titration is between strong acid and weak base

(1aiii)
(i) volumetric flask
(ii) conical flask

(1aiv)
I – Yellow
II – Pink.

(1bi)
500cm³ contains 0.1mole
:. 1000cm³ will contain
= 0.1/1000/500
= 0.2mol/dm³

(1bii)
Molar mass of HCl = 1+35.5 = 36.5g/mol
Concentration of A in mol/dm³
= Conc. Of A in g/moldm-³/Molar mass of A
0.2 = Conc. Of A in g/moldm-³/36.5
Conc. of A in g/dm³ = 0.2*36.5
= 7.3g/dm³

(1biii)
CAVA/CBVB = nA/nB
CB = CAVAnB/VBnA
CB = 0.2*24*5*1/25*2
CB = 0.098mol/dm³
:. Concentration of B in moldm-³ = 0.098mol/dm³

(1biv)
Concentration of B in g/dm³
250cm³ contains 7.15g of Na2CO3.nH20
:. 1000cm³ will contain
= 7.15*1000/250 = 28.6g/dm³

(1bv)
Volume of N in Na2CO3.nH20
Conc. of B in mol/dm³ = Conc. of B in g/dm³/Molar mass
0.098 = 28.6/Molar mass
Molar mass = 28.6/0.098
= 291.84g/mol
Na2CO3.nH20 = 291.84
(23*3)+12+(16*3)+n((1*2)+16) = 291.84
46+12+8+18n = 291.84
106+18n = 291.84
18n = 291.84 – 106
18n = 185.84
n = 185.84/18 = 10.3
n = 10

(1bvi)
Percentage of water of crystallization = 10H2O/291.84 * 100/1
= 10(18)/291.84 = 180/291.84
= 61.7%
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(2ai)
OBSERVATIONS;
C dissolved in distilled water to form solution

(2aii)
INFERENCE
Ca²+, Pb²+, Al³+ or Pb²+ present

(2aiii)
INFERENCE
Ca²+ present

(2aiv)
INFERENCE
Ca ²+ present

(2av)
OBSERVATIONS
a white precipitate is formed

(2bi)
INFERENCE
Co² gas from Co²,³ ^- or HCO^-³ confirmed

(2bii)
INFERENCE
Co² gas confirmed

(2biii)
INFERENCE
Ca O present
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(3ai)
(i) Soda line is used because it does not attack glass
(ii) The delivery tube is withdrawn immediately heating is stopped to prevent the sucking back of water into the flask

(3aii)
(i) This is due to the formation of metallic silver which changes the colour to grey
(ii) A white fume are formed

(3bi)
(i) Rhetort stand
(ii) Separating funnel

(3bii)
Separating funnel method

(3biii)
The lower denser liquid distill first

(3biv)
It has higher density

Completed

Enjoy!!!

1 Comment

  1. I really lack a word on how to comment you people, only God can reward, and ours is always prayers for your protection against your enemies, and finally the Chemistry practical for today’s NECO GCE is incomplete pls help us with the remaining, thank you

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