1.1. A student investigated the speed of reaction when iodine was produced by the reaction of solution L with potassium iodide at different temperatures. Five experiments were carried out.

Experiment 1

A burette was filled with the aqueous solution L to the 0.0 cm³ mark.

10.0 cm³ of solution L was added from the burette into a boiling tube and the initial temperature of the solution was measured. Using a measuring cylinder, 5 cm³ of aqueous potassium iodide and 3 cm³ of aqueous sodium thiosulfate were poured into a second boiling tube. Starch solution was added to this boiling tube and the mixture shaken.

The mixture in the second boiling tube was added to the solution L, shaken and the clock started. These chemicals reacted to form iodine which reacted with the starch. When a blue colour appeared, the clock was stopped and the time measured and recorded in the table. The final temperature of the mixture was measured.

Experiment 2

Experiment 1 was repeated but solution L was heated to about 40 °C. The temperature of the solution was measured before adding the mixture in the second boiling tube. When a blue colour appeared, the clock was stopped and the time measured and recorded in the table. The final temperature of the mixture was measured.

Experiment 3

Experiment 2 was repeated, heating solution L to about 50 °C.

Experiment 4

Experiment 2 was repeated, heating solution L to about 60 °C.

Experiment 5

Experiment 2 was repeated, heating solution L to about 70 °C.

Use the thermometer diagrams in the table to record the temperatures and complete the table.

1.2. Plot the results on the grid below and draw a smooth line graph.

1.3. From your graph, work out the time taken for the blue colour to appear if solution L was heated to 80 °C. The final temperature of the reaction mixture was 64 °C. Show clearly on the grid how you obtained your answer.

1.4. Suggest the purpose of the starch solution in the experiments.

1.5. i) In which experiment was the reaction speed fastest?

[1]

ii) Explain, using ideas about particles, why this experiment was the fastest.

[2]

1.6. Predict the effect on the time and speed of the reaction in Experiment 5 if it was repeated using a less concentrated solution of L.

Time: ..............................................................

Speed: .............................................................. 

1.7. Why was a burette used to measure solution L instead of a measuring cylinder?