1.1. A student investigates the rate of reaction between copper sulfate solution and dilute sodium hydroxide solution.

75 cm³ of copper sulfate solution was poured into a 250 cm³ conical flask using a measuring cylinder.

The conical flask was then placed on a cross drawn on a piece of paper. 15 cm³ of dilute sodium hydroxide was added to the conical flask as shown.

The timer was started, and then was stopped when the cross could not be seen anymore. The student then recorded the time. 

i) Write down the equation for the reaction between copper sulfate and dilute sodium hydroxide. Include state symbols.

ii) Explain why the cross on the paper disappears.

iii) Give the name of the product formed in the reaction that causes the cross on the paper to disappear.

1.2. The student investigates the effect of temperature on the rate of the reaction, described in part (a), using the following procedure.

Procedure

1. Measure out copper sulfate using a beaker and pour it into a conical flask.

2. Record the initial temperature of the copper sulfate in the conical flask using a thermometer.

3. Place the flask with the solution onto a cross drawn on a piece of paper.

4. Heat the sodium hydroxide to a specific temperature.

5. Start the stopwatch and then add the dilute sodium hydroxide.

6. Stop the stopwatch when the cross can no longer be seen.

7. Repeat the experiment at different temperatures.

i) Identify one key mistake and one improvement to the students method. 

ii) Suggest two control variables which should remain constant during this experiment.

1.3. The student concludes that the rate of reaction increases with increasing temperature.

Explain whether the student’s conclusion is correct using the collision theory.