WAEC CHEMISTRY PRACTICAL ANSWERS 2021

WAEC CHEMISTRY PRACTICAL ANSWERS 2021

Here is the waec chemistry practical answers for 2021.

Chemistry practical answers

3ai

The titre value would be higher than 23.50cm³.

3aii
This is because when distilled water was added to the base , the base becomes less concentrated , hence it’s easier to titrate than a concentrated base.

3bi no reaction occurs , copper is less electropositive than Zinc , so cannot displace it in the reaction.
ii), KOH is a deliquescent compound, so it would absorb water from the atmosphere to form sticky particle in the watch glass.
III), when few drops of phenolphthalein is dropped in the watch glass , it changes colour to pink because it’s a basic solution (KOH).

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(1a)

Volume of burrete = 50.00cm³

Volume of pipette = 25.00cm³

Indicator = Methyl orange

TABULATE

Final burette readings (cm³); 37.50 | 22.50 | 37.50 | 44.50

Initial burette readings(cm³); 0.00 | 0.00 | 0.00 | 0.00

Volume f Acid used (cm³); 37.50 | 22.50 | 22.50 | 22.50

Volume of A used = 1st + 2nd + 3rd/3

= 22.50+22.50+22.50/3

Average volume of A used = 22.50cm³

(1bi)

Concentration of A ( CA )?

2.03g in 500cm³ of solution

Volume = 500cm³/1000 = 0.500dm³

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In g/dm³ = 2.03/0.5 = 4.06g/dm³

To find concentration in mol/dm³

Conc. of A in mol/dm³ = Conc. of A in g/dm³/Molar mass

Conc. of A in mol/dm³ = 4.06/36.5

= 0.1112mol/dm³

Molar mass of A (HCL) = 1+35.5 = 36.5g/mol

(1bii)

Number of mole of the Acid in average titre

Na = CaVa

= 0.1112 × 22.50

= 2.52moles

(1biii)

Nb= ? Na= 3, Ca= 0.1112mol/dm³, Cb = 0.12mol/dm³ , Va = 22.50cm³, Vb = 50.00cm³

CaVa/CbVb= nA/nB

0.1112×22.50/0.12×50 = 3/nB

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nB × 2.502 = 18

nB = 18/2.502 =

:. nB = 7.194moles

= 7moles(approx.)

(1biv)

Mole ratio of Acid to base

nA:nB = 7:3

We gat you..

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