Chemistry · Oct / Nov 2025 · Paper 11 · Question 11

A mixture of sodium hydrogencarbonate and sodium chloride is heated. The equation for the reaction that takes place when sodium hydrogencarbonate is heated is shown. 2NaHCO$_3$(s) → Na$_2$CO$_3$(s) + CO$_2$(g) + H$_2$O(g) Sodium chloride is unchanged on heating. When 6.0 g of the mixture is heated, the loss in mass is 1.5 g. What is the percentage by mass of sodium hydrogencarbonate in the mixture? [relative molecular mass, $M_r$: NaHCO$_3$, 84; Na$_2$CO$_3$, 106; CO$_2$, 44; H$_2$O, 18]

1. A34%
2. B48%
3. C68%
4. D95%

As printed in the paper