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).

(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

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

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..