A student heats green copper carbonate in an open boiling tube. The solid turns black and a gas is given off.
CuCO3(s)→CuO(s)+CO2(g)\mathrm{CuCO_{3}(s)} \rightarrow \mathrm{CuO(s)} + \mathrm{CO_{2}(g)}CuCO3(s)→CuO(s)+CO2(g)
The student records these masses.
| Measurement | Mass / g |
|---|---|
| boiling tube and copper carbonate before heating | 27.47 |
| boiling tube and contents after heating | 26.81 |
Give the name of the black solid.
Calculate the decrease in mass.
A student says the decrease in mass shows that mass is not conserved in this reaction. Explain why the student is wrong.
Relative formula masses: CuCO3=123.5,CuO=79.5,CO2=44\mathrm{CuCO_{3}} = 123.5, \mathrm{CuO} = 79.5, \mathrm{CO_{2}} = 44CuCO3=123.5,CuO=79.5,CO2=44. Use these values to show that the equation obeys the law of conservation of mass.
The student heats the boiling tube again. The mass decreases further. Explain what this shows and what the student should do next.
55 exam-style questions on Edexcel GCSE Chemistry 2.6 Calculations involving masses, covering 2.6.1 Relative formula mass and percentage composition, 2.6.2 Empirical and molecular formulae, 2.6.3 Conservation of mass, 2.6.4 Reacting masses and concentration in g dm⁻³, 2.6.5 The mole and the Avogadro constant, and 2.6.6 Limiting reactants and stoichiometry. Each one has a worked solution and a mark scheme showing where the marks go.