This question is about the formulae of some substances found in a school laboratory.
The table shows the names and formulae of five substances.
| Substance | Formula |
|---|---|
| oxygen | O₂ |
| water | H₂O |
| carbon dioxide | CO₂ |
| ammonia | NH₃ |
| sodium chloride | NaCl |
Which substance in the table is an element?
How many atoms are there in one molecule of ammonia?
A compound contains one calcium atom, one carbon atom and three oxygen atoms.
Write the formula of this compound.
Iron reacts with chlorine to make iron chloride.
Balance the equation for this reaction.
...... Fe + 3 Cl₂ → ...... FeCl₃
Hydrogen burns in oxygen to make water.
A student tries to balance the equation for this reaction like this:
H2+O2→H2O2 \mathrm{H_{2} + O_{2} \rightarrow H_{2}O_{2}} H2+O2→H2O2Explain why the student's method is not correct.
Write the correct balanced equation.
55 exam-style questions on OCR GCSE Chemistry 3.1 Introducing chemical reactions, covering 3.1.1 Writing formulae and balanced chemical equations, 3.1.2 Formulae of compounds from ions, and state symbols, 3.1.3 Conservation of mass and observed changes in mass, 3.1.4 Half equations and balanced ionic equations, 3.1.5 The mole and the Avogadro constant, and 3.1.6 Stoichiometry, limiting reactants and reacting masses. Each one has a worked solution and a mark scheme showing where the marks go.