Required practical 7a

Question 1

What is the experiment known as

Answer 1

iodine clock

Question 2

What sort of method is used

Answer 2

Initial rates

Question 3

What happens during the reaction

Answer 3

Hydrogen peroxide reacts with iodide ions to form iodine, and the thiosulfate ions immediately react with the iodine

Question 4

What are the equations for the reaction

Answer 4

1. H2O2 + 2H+ + 2I- –> I2 + 2H2O
2. I2 + 2S2O32- –> 2I- + S4O62-

Question 5

What is the role of the S2O32- ions

Answer 5

Remove the iodine as it is formed

Question 6

Step 1

Answer 6

Fill a 50cm3 burette with potassium iodide solution

Question 7

What should be done before filling the burette

Answer 7

Rinse through with potasium iodide

Question 8

Step 2

Answer 8

Transfer 10cm3 hydrogen peroxide into a clean dry 100cm3 beaker from a burette

Question 9

Step 3

Answer 9

Use a 50cm3 measuring cyclinder to transfer 25cm3 sulfuric acid into a clean, dry 250cm3 beaker

Question 10

Step 4

Answer 10

Use a 25cm3 measuring cylinder to transfer 20cm3 distilled water into the beaker

Question 11

Step 5

Answer 11

Using a dropping pipette, add 1cm3 starch solution into the beaker

Question 12

Step 6

Answer 12

Use the burette to add 5cm3 potassium iodide into the beaker

Question 13

Step 7

Answer 13

Finally, add 5.0 cm3 sodium thiosulfate into the beaker from the burette

Question 14

Step 8

Answer 14

Stir the mixture and add the hydrogen peroxide

Question 15

What should be done as the hydrogen peroxide is added

Answer 15

Immediately start the timer

Question 16

Step 9

Answer 16

Stop the timer when the mixture turn blue-black and record the time

Question 17

Step 10

Answer 17

Rinse the beaker with distilled water and dry with a paper towel

Question 18

Step 11

Answer 18

Repeat the experiment a few more times, changing the concentration of potassium iodide

Question 19

What does repeating the experiment and changing the concentration of potassium iodide allow

Answer 19

The order of reaction with respect to potassium iodide can be established

Question 20

Analysis

Answer 20

Plot a graph of 1/t (on y axis) and conc (on the x axis)