To determine the rate equation of a chemical reaction, a student must select an appropriate technique for continuously monitoring the reaction mixture.
Which of the following reactions is paired with the most appropriate method for continuous monitoring?
Reaction: Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)\text{Zn}(s) + 2\text{HCl}(aq) \rightarrow \text{ZnCl}_2(aq) + \text{H}_2(g)Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)
Method: Continuous measurement of the mass of the reaction vessel using a standard laboratory balance.
Reaction: CH3COCH3(aq)+I2(aq)→H+CH3COCH2I(aq)+H+(aq)+I−(aq)\text{CH}_3\text{COCH}_3(aq) + \text{I}_2(aq) \xrightarrow{\text{H}^+} \text{CH}_3\text{COCH}_2\text{I}(aq) + \text{H}^+(aq) + \text{I}^-(aq)CH3COCH3(aq)+I2(aq)H+CH3COCH2I(aq)+H+(aq)+I−(aq)
Method: Colorimetry to measure the change in light absorbance of the solution over time.
Reaction: CH3COOCH2CH3(aq)+H2O(l)→H+CH3COOH(aq)+CH3CH2OH(aq)\text{CH}_3\text{COOCH}_2\text{CH}_3(aq) + \text{H}_2\text{O}(l) \xrightarrow{\text{H}^+} \text{CH}_3\text{COOH}(aq) + \text{CH}_3\text{CH}_2\text{OH}(aq)CH3COOCH2CH3(aq)+H2O(l)H+CH3COOH(aq)+CH3CH2OH(aq)
Method: Using a gas syringe to continuously measure the volume of ethanol vapor produced.
Reaction: S2O82−(aq)+2I−(aq)→2SO42−(aq)+I2(aq)\text{S}_2\text{O}_8^{2-}(aq) + 2\text{I}^-(aq) \rightarrow 2\text{SO}_4^{2-}(aq) + \text{I}_2(aq)S2O82−(aq)+2I−(aq)→2SO42−(aq)+I2(aq)
Method: Using a pH meter to continuously monitor the change in pH.
91 exam-style questions on OCR GCSE Chemistry Monitoring chemical reactions. Each one has a worked solution and a mark scheme showing where the marks go.