Gas volume answer 1

An experiment requires the measurement of a volume of carbon dioxide gas formed by the reaction between potassium carbonate solid and hydrochloric acid. The equation is:

K₂CO₃(s) + 2HCl(aq) ⇒ 2KCl(aq) + H₂O(l) + CO₂(g)

It is proposed to collect the gas over water in an inverted 250 cm³ measuring cylinder. Suggest appropriate quantities of potassium carbonate and acid for this experiment.

A gas volume of around 150 cm³ gives us quite a large volume to reduce measurement errors without filling the cylinder too full.

150 cm³ = 150/24000 = 0.00625 mol

From the equation, K₂CO₃ º CO₂

So we need 0.00625 mol of K₂CO₃

K₂CO₃ = 138

\mass of K₂CO₃ = 138 × 0.00625 = 0.86 g

Also from the equation, K₂CO₃ º 2HCl

\moles of HCl = 2 × 0.00625 = 0.0125 mol

Dilute, 1.0 M HCl should be readily available

Volume of acid required = 0.0125/1.0 = 0.0125 dm³ = 12.5 cm³

It would be better to use an excess of acid to ensure complete reaction of the carbonate. So use 15 cm³ of 1.0 M hydrochloric acid.