PAG 9 - Rates of reactions - Continuous Monitoring Method

Question 1

What is the role of manganese 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 the word and chemical equations
for the 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 the half-life of

the decomposition of hydrogen peroxide

Answer 6

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

Question 7

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

Answer 7

[H2O2] (in mol dm3) =
(40 - V(O2))
——————
240

Question 8

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

Answer 8

The reaction will have started so O2
 will
be produced. If the bung is not in place,
oxygen will be escape (this won’t be
included in the 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