Describe how you would measure the rate of a reaction between sodium thiosulfate and hydrochloric acid. Include the apparatus you would use.

To measure the rate of reaction, I would use a conical flask to mix sodium thiosulfate and hydrochloric acid. I would place a piece of paper with a cross underneath the flask and time how long it takes for the cross to disappear as the solution turns cloudy. This answer is anchored to AS apparatus and techniques.

To measure the rate of reaction, I would use a conical flask to mix sodium thiosulfate and hydrochloric acid. I would place a piece of paper with a cross underneath the flask and time how long it takes for the cross to disappear as the solution turns cloudy. is the best answer because it directly supports the AQA A-Level Chemistry objective to measure reaction rates using appropriate methods. This reasoning is anchored to AS apparatus and techniques in AS practical skills and required practical activities, and it separates rates from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.