CP13b

Question 1

How can you determine the initial rate of reaction from a concentration time graph

Answer 1

tangent at t=0

Question 2

Explain the role of starch in this experiment

Answer 2

acts as an indicator
shows the presence of excess iodine

Question 3

What colour change is observed with the presence of starch

Answer 3

colourless to blue black

Question 4

Why is this experiment an example of the initial rate monitoring method

Answer 4

one experiment is carried out at each concentration and time is measured for the colour change to occur

Question 5

Why is it important to keep the number of moles of sodium thiosulfate fixed

Answer 5

acts as a control variable
changing the concentration of sodium thiosulfate would affect the initial rate of reaction

Question 5

Why is the calculated initial rate an estimate rather than the true value

Answer 5

time is taken for the iodine to react with the sodium thiosulfate
this is a short period of time so the measured initial rate is not a fully accurate measure of the first time they react

Question 6

Why is water added to the reaction mixture

Answer 6

to keep the total volume of solution constant

Question 7

How is concentration varied

Answer 7

by dilution

Question 8

What graph is plotted for this reaction

Answer 8

1/time against concentration
1/time is proportional to rate