RP 7 - Measuring rate of a reaction

Question 1

What is meant by rate of reaction?

Answer 1

The change in concentration of reactants or products overtime

Question 2

How come rate of reaction be measured?

Answer 2

• Initial rates method
• A continuous monitoring method

Question 3

What is an initial rate method?

Answer 3

The method involves measuring the initial rate of reaction for multiple different concentrations to observe how rate of reaction varies

Question 4

What is an example of an initial rate method?

Answer 4

The iodine clock experiment:

• The iodine produced reacts with all of the thiosulphate ions present. Excess iodine remains in solution which then reacts with starch to form a blue black solution.
• Time how long it takes for this blue black colour to appear.

Question 5

What are some issues with the iodine clock experiment?

Answer 5

• Some low iodine concentrations may take too long to react
• Delayed stopwatch reactions
• Concentrations may not be exact due to measuring apparatus

Question 6

What is a continuous monitoring method?

Answer 6

This involves measuring the change in concentration of reactant or product overtime (or me measuring the volume of gas released) as the reaction progresses

Question 7

Give an example of a continuous monitoring method

Answer 7

1) Add a 6 cm strip of magnesium ribbon into a conical flask containing hydrochloric acid and place a bug in the top of the flask and start the timer.
2) Note down the volume of hydrogen gas collect every 15 seconds for a period of 2.5 minutes.
3) Repeat for different hydrochloric acid concentration.

Question 8

How would you analyse the data from the continuous monitoring method experiment?

Answer 8

1) Plot of volume of hydrogen gas produced against time for each concentration of hydrochloric acid and draw a line of best fit.
2) Draw a tangent at t=0 for each line.
3) To deduce the rate of each reaction calculate the gradient of each tangent.
4) Compare the calculated rate values.

Question 9

What are some issues with the continuous monitoring method experiment?

Answer 9

• Some gas may escape before the bung is added
• The magnesium strips may be of different mass and surface area which will affect the rate of reaction

Question 10

How do you prevent gas escaping?

Answer 10

Place the solid reactant upright inside a sample tube in the conical flask tipping the tube over by moving the Chronicle flask around to start the reaction