Sodium hydrogencarbonate, NaHCO3\mathrm{NaHCO_{3}}NaHCO3, is used in baking powder. When it is heated, it decomposes to form sodium carbonate, water and carbon dioxide.
A student heats 8.40 g of sodium hydrogencarbonate in a crucible until the mass stays constant. The mass of solid sodium carbonate left is 5.30 g.
Relative formula masses: NaHCO3=84,Na2CO3=106,CO2=44\mathrm{NaHCO_{3}} = 84, \mathrm{Na_{2}CO_{3}} = 106, \mathrm{CO_{2}} = 44NaHCO3=84,Na2CO3=106,CO2=44
Sodium hydrogencarbonate contains Na+\mathrm{Na^{+}}Na+ and HCO3−\mathrm{HCO_{3}^{-}}HCO3− ions. Sodium carbonate contains Na+\mathrm{Na^{+}}Na+ and CO32−\mathrm{CO_{3}^{2-}}CO32− ions. Explain why the formula of sodium carbonate has two sodium ions but the formula of sodium hydrogencarbonate has only one.
Calculate the total mass of water and carbon dioxide given off.
Use the masses to deduce the balanced equation for the decomposition. Include state symbols.
Explain why the student heated the solid until the mass stayed constant.
Sodium hydrogencarbonate also reacts with excess dilute hydrochloric acid:
NaHCO3(s)+HCl(aq)→NaCl(aq)+H2O(l)+CO2(g)\mathrm{NaHCO_{3}(s)} + \mathrm{HCl(aq)} \rightarrow \mathrm{NaCl(aq)} + \mathrm{H_{2}O(l)} + \mathrm{CO_{2}(g)}NaHCO3(s)+HCl(aq)→NaCl(aq)+H2O(l)+CO2(g)
A student claims that 8.40 g of sodium hydrogencarbonate produces the same mass of carbon dioxide whether it is heated or reacted with excess acid. Evaluate this claim. Use calculations in your answer.
230 exam-style questions on Edexcel GCSE Chemistry 1.1 Formulae, equations and hazards, covering 1.1.1 Formulae, word and balanced equations, 1.1.2 Balanced ionic equations, and 1.1.3 Hazard symbols and risk in practical work. Each one has a worked solution and a mark scheme showing where the marks go.