2023 N.E.C.O (CHEMISTRY PRACTICAL) Questions & Answers {Nigeria}

THURSDAY, 13th July, 2023

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(1a)

Burette Reading (cm³)	Rough	Titration I	Titration II
Final Reading (cm³)	21.50	43.00	22.00
Initial Reading (cm³)	0.00	21.50	00.00
Volume of A used (cm³)	21.50	21.50	22.00

(1ai)

Average Volume of acid used = 21.50 + 21.50/2 = 21.50cm³

(1aii)

Solution B

[Sodium trioxocarbonate 

(iv)] feels soapy

(1bi)

Conc. B in mol/dm³ =?

Ca= 0.04, Va= 21.50cm³, na= 1

Cb= ? , Vb= 25.00cm³ nb= 1

CaVa/CbVb = na/nb = 0.04×21.50/Cb×25.00 = 1/1

Cb= 0.04×21.50/25.00 = 0.86/25.00

Cb= 0.0344mol/dm³

(1bii)

Conc. of B in g/dm³ = Conc. of B in mol/dm³ × molar mass of B

Molar mass of B(NaCO₃)= (23×2) + 12 + (16×3) = 106

:. Conc. of B in g/dm³ = 0.0344×106 = 3.6g/dm³

(1biii)

1 mole of Na₂Co₃ = 1mole of Na₂So₄

:.  0.0344 mole of Na₂Co₃ = 0.0344 mole of Na₂So₄

№ of mole= mass/ molar mass

Molar mass of Na₂So₄= (23×2)+32+(16×4)=142

:. 0.0344 = mass/142

Mass=142×0.0344=4.9g

(1biv)

1 mole of Na₂Co₃= 1 mole of CO₂

0.0344 mole of Na₂Co₃ = 0.0344 mole of CO₂

:. № of mole = volume/ molar volume = 0.0344 = volume of CO₂/22400cm³

=771cm³

(2a)

(3ai) 

Sulphur (iv) oxide and hydrogen sulphide.

(3aii)

Liberation of hydrogen gas with pop sound and formation of green iron (ii) chloride solution

(3aiii)

Spatula, beaker, weighing balance,  standard volumetric flask 

(3bi) 

Solution turns red

(3bii) 

Turns from brown to green

(3biii)

 A colourless, odourless, acidic gas liberated which turns blue litmus paper red and turn lime water milky.