Question

(iii) The filtrate was an alkaline solution of potassium carbonate. This was titrated

against a standard hydrochloric acid solution to find the concentration of the
potassium carbonate.
K₂CO₂ + 2HC1
2KCI+ CO₂ + H₂O
Methyl orange was used as an indicator, this turns from yellow in the potassium
carbonate solution to pink when the potassium carbonate is neutralised by the
hydrochloric acid. The following results were obtained using 25.00 cm³ samples of
the potassium carbonate solution.
Burette finish/cm³
Burette start / cm³
24.80
0.00
26.20
1.60
26.55
2.00
I Calculate the mean volume of hydrochloric acid added, using all three sets
of results.
[1]
(b) In another experiment Penny obtained white crystals of potassium carbonate, K₂CO3,
from the wood ash.
(1) Show that the percentage by mass of potassium in K₂CO, is 56.6.
[2]
Ans
SESTS

Answer 1

h

Step-by-step explanation:

I. To calculate the mean volume of hydrochloric acid added, you need to find the average of the three values obtained from the burette readings.

First set: 24.80 - 0.00 = 24.80 cm³

Second set: 26.20 - 1.60 = 24.60 cm³

Third set: 26.55 - 2.00 = 24.55 cm³

The mean volume of hydrochloric acid added is (24.80 + 24.60 + 24.55) / 3 = 24.66 cm³

b. (1) To find the percentage of potassium in K₂CO₃, you need to calculate the mass of potassium in the compound and divide it by the total mass of the compound, then multiply by 100.

The relative atomic mass of potassium is 39.1 and the relative atomic mass of carbon is 12.01 and oxygen is 16.00.

So, the mass of potassium is 2 x 39.1 = 78.2 g.

The mass of carbon is 1 x 12.01 = 12.01 g.

The mass of oxygen is 3 x 16.00 = 48.00 g.

The total mass of the compound is 78.2 + 12.01 + 48.00 = 138.21 g.

The percentage by mass of potassium in K₂CO₃ is (78.2 / 138.21) x 100 = 56.6%.