Rate Of Reaction = Iodine And Propanone

Question 1

What is the reaction we are monitoring?

Answer 1

Propanone + iodine + acid catalyst ——> iodide ions

Question 2

How do we monitor propanone + iodine?

Answer 2

By taking samples of the reaction mixture at various time points in a reaction and quenching with sodium hydrogen carbonate

Question 3

Why do we use sodium hydrogen carbonate in particular to quench the reaction?

Answer 3

Because it neutralises the acid catalyst so stops the reaction at this point

Question 4

Why is quenching the reaction required?

Answer 4

So it stops the reaction at this point (freezes it) so the concentration remains the same
So we have time to Titrate it

Question 5

What continuous monitoring method do we use to measure the rate of reaction?

Answer 5

Titration with thiosulfate ions

Question 6

When thiosulfate solution in the burette is added, what does it react with?

Answer 6

Any remaining iodine ions that have NOT reacted

Question 7

The volume of thiosulfate added is proportional to…

Answer 7

The concentration of iodine remaining in the conical flask because all the thiosulfate that is added will immediately react with iodine
So, the concentration of iodine at this point in the reaction between propanone and iodine

Question 8

Indicator for the titration

Answer 8

Starch

Question 9

Starch as an indicator is added…

Answer 9

Towards the end point of the titration

Question 10

Why is starch added toward the end of the titration in the conical flask?

Answer 10

Because starch in iodine turns blue black, so the colour change is difficult to see

Question 11

Colour change using starch indicator

Answer 11

Yellow brown solution to colourless

Question 12

When is starch added?

Answer 12

Toward the end of the titration (when solution is pale yellow) to see if the solution turns blue black to indicate some iodine is still in the conical flask thus hasn’t been fully reacted

Question 13

This reaction with respect to iodine is

Answer 13

0 order

Question 14

This reaction with respect to acid catalyst is

Answer 14

1 order

Question 15

This reaction with respect to propanone is

Answer 15

1 order

Question 16

How is this experiment repeated?

Answer 16

Repeat by withdrawing samples every 5 minutes with a pipette from the reaction mixture to find the concentration of iodine at a new point in time

Question 17

How do we form the reaction mixture?

Answer 17

Large excess acid catalyst and propanone so they have no effect on the rate of reaction, so we can monitor the effect of iodine only on rate of reaction to find its order