PAG 09: Rates of Reaction- Continuous Monitoring Method

Question 1

What is role of magnesium dioxide in the decomposition of hydrogen peroxide?

Answer 1

Catalyst

Question 2

What is the purpose of catalysts?

Answer 2

• Provide an alternative reaction route with a lower activation energy
• Increase the rate of reaction

Question 3

Write word and chemical equations for reaction involving manganese(IV) oxide and hydrogen peroxide

Answer 3

Hydrogen peroxide -> water + oxygen
2H2O2 -> 2H2O + O2
(MnO2 isn’t included as it is a catalyst)

Question 4

Describe how to set up the apparatus to measure the volume of gas produced during a reaction

Answer 4

A gas syringe or an upside-down water-filled measuring cylinder in a trough of water may be used to collect the gas

Question 5

What is meant by term ‘half-life’ for a reaction?

Answer 5

The time taken for the reactant concentration to half

Question 6

Briefly describe how to find half-life of the decomposition of hydrogen peroxide

Answer 6

1. Set up the apparatus to collect any gas produced during the reaction
2. React volume of O2 collected at regular intervals and calculate [H2O2]
3. Plot graph of [H2O2] against time and use it to find 2 values for half-life

Question 7

What formula can be used to calculate [H2O2] from volume of oxygen collected?

Answer 7

[H2O2] (in mol dm^-3)= (40-V(O2))/240

Question 8

Why is it important to rapidly put the bung in the conical flask after H2O2 and catalyst have been combined?

Answer 8

Reaction will have started so O2 will be produced. If the bung is not in place, oxygen will escape (this won’t be involved in volume measurement)

Question 9

Why might the volume of gas be measured in a burette rather than a measuring cylinder?

Answer 9

To obtain more precise measurements