1.1. A student uses this apparatus to investigate the rate of reaction between calcium carbonate chips and dilute hydrochloric acid.

Every 20 seconds the student records the reading on the balance.

Explain why using a cotton wool plug increases the accuracy of the student’s results.

1.2. Complete the equation for the reaction by adding the state symbols.

CaCO₃ (..........) + 2HCl (..........) → CaCl₂ (aq) + H₂O (..........) + CO₂ (..........)

1.3. The student uses the balance readings to find the decrease in mass of the flask and contents.

The graph shows the student’s results.

 i) Give a reason why there are some calcium carbonate chips remaining in the flask when the reaction stops.

 (1)

 ii) State how the student would know when the reaction has stopped.

 (1)

 iii) Use the graph to determine the amount, in moles, of carbon dioxide produced during the reaction.

 [M_r of CO₂ = 44]

 (2)

 amount = .............................. mol

 iv) Use the graph to calculate the rate of reaction, in grams per second, at time 60 seconds.

 Show your working on the graph.

 (3)

 rate of reaction = .............................. g / s

1.4. The student repeats the investigation by diluting the original hydrochloric acid. 

The student then determines the initial rate of reaction at different percentage concentrations of the original hydrochloric acid. 

The graph shows the student’s results.

 i) Describe the relationship between the initial rate of reaction and percentage concentration of the original hydrochloric acid.

 (2)

 ii) Explain why changing the concentration of hydrochloric acid has an effect on the initial rate of reaction.

 (2)