Indium (Ar=114.8A_r = 114.8Ar=114.8) reacts with dilute aqueous acid in a redox reaction, forming a solution and hydrogen gas. A student proposed three possible ionic equations for this reaction, forming indium ions with different charges:
Equation 1: 2In(s)+2H+(aq)→2In+(aq)+H2(g)2\text{In(s)} + 2\text{H}^+\text{(aq)} \rightarrow 2\text{In}^+\text{(aq)} + \text{H}_2\text{(g)}2In(s)+2H+(aq)→2In+(aq)+H2(g)
Equation 2: In(s)+2H+(aq)→In2+(aq)+H2(g)\text{In(s)} + 2\text{H}^+\text{(aq)} \rightarrow \text{In}^{2+}\text{(aq)} + \text{H}_2\text{(g)}In(s)+2H+(aq)→In2+(aq)+H2(g)
Equation 3: 2In(s)+6H+(aq)→2In3+(aq)+3H2(g)2\text{In(s)} + 6\text{H}^+\text{(aq)} \rightarrow 2\text{In}^{3+}\text{(aq)} + 3\text{H}_2\text{(g)}2In(s)+6H+(aq)→2In3+(aq)+3H2(g)
The student carried out an investigation to determine which equation is correct using dilute hydrochloric acid. The results were:
Assume conditions are room temperature and pressure (RTP) where 1 mol1\text{ mol}1 mol of gas occupies 24000 cm324000\text{ cm}^324000 cm3.
Analyse the student's results to conclude which of Equation 1, 2, or 3 is supported by the experimental results.
Predict how a heated apparatus during the reaction (making the gas mixture hot) would affect the gas volume collected and the conclusion in (a). Explain your answer.
The student modifies the method: 1.15 g1.15\text{ g}1.15 g (0.01 mol0.01\text{ mol}0.01 mol) of indium is reacted with excess dilute hydrochloric acid, then excess aqueous sodium hydroxide is added. A precipitate forms, which is collected, dried, and weighed. Explain how the mass of precipitate formed allows the student to conclude which of the equations is correct.
199 exam-style questions on OCR A A Level Chemistry Atoms and reactions, covering Atomic structure and isotopes, Compounds, formulae and equations, Amount of substance, Acids, and Redox. Each one has a worked solution and a mark scheme showing where the marks go.