Question 1a

Marks: 2

a)

A group of students planned how to investigate the effect of changing the concentration of H₂SO₄ on the initial rate of reaction with magnesium:

Mg (s) + H₂SO₄(aq)

\to

MgSO₄ (aq) + H₂ (g)

They decided to measure how long the reaction took to complete when similar masses of magnesium were added to acid.

Two methods were suggested:

Method 1 - Use small pieces of magnesium ribbon, an excess of acid and record the time taken for the magnesium ribbon to disappear

Method 2 - Use large strips of magnesium ribbon, an excess of magnesium and record the time taken for bubbles to stop forming

Deduce, giving a reason, which of method 1 and method 2 would be the least affected if the masses of magnesium ribbon used varied slightly between each experiment.

[2]

Key Concepts

Rate experiments

Question 1b

Marks: 2

b)

Neither method in part a) actually allows the initial rate to be calculated. Outline a method that would allow the calculation of initial rate.

[2]

Key Concepts

Rate experiments

Question 1c

Marks: 1

c)

The reaction is to be conducted across a few weeks.

State a factor that has a significant effect on reaction rate, which could vary between experiments across the weeks and therefore needs to be controlled.

[1]

Key Concepts

Rate experiments

Question 1d

Marks: 4

d)

One group collected the following data using 1.50 mol dm^-3acid:

Trial	Time/ s ( $\pm$ 0.01 s)
1	91.56
2	98.33
3	72.08
4	89.41

i)

Comment on the use of the uncertainty when calculating the mean.

[2]

ii)

Calculate the mean time for the set of results.

[2]

Key Concepts

Propagation of errors
Impact of errors

Question 2a

Marks: 5

a)

When investigating the reaction between sulfuric acid and calcium carbonate, it was observed that a small increase of temperature of around 10 ^oC caused a doubling in the rate of the reaction.

Sketch and label Maxwell-Boltzmann curve for the two temperatures T and T+10, and use this diagram to help to explain this effect of temperature on rate.

[5]

Key Concepts

Explaining rates
Maxwell-Boltzmann curves

Question 2b

Marks: 2

b)

Why do some collisions at high temperatures still not result in the formation of the product?

[2]

Key Concepts

Explaining rates

Question 2c

Marks: 3

c)

Identify and explain another factor that affects the number of particles present in a solution with sufficient energy to react.

[3]

Key Concepts

Explaining rates

Question 2d

Marks: 2

d)

Some groups investigating the effect of temperature on rate stirred their reactions, some did not.

Explain the effect of stirring upon the rate of the reaction.

[2]

Key Concepts

Explaining rates

Question 3a

Marks: 5

a)

0.5 g of magnesium reacts with 50 cm³ of 0.01 moldm^-3 nitric acid. Magnesium is in excess.

A graph monitoring the volume of hydrogen gas produced is shown below:

6-1-ib-sl-sq-hard-q3a-rate-of-reaction-graph

i)

Calculate the mean rate of reaction over the first 15 seconds of the reaction

[1]

ii)

Calculate the actual rate of reaction at 15 seconds

[3]

iii)

Explain the difference in values for rate

[1]

Key Concepts

Rate experiments
Measuring rates

Question 3b

Marks: 3

b)

Compare the expected rate and progress of the reaction if 25 cm³ of 0.2 mol dm^-3 nitric acid was used instead of 50 cm³ of 0.1 mol dm^-3 nitric acid.

[3]

Key Concepts

Rate experiments
Measuring rates

Question 3c

Marks: 2

c)

Suggest one change to the reaction that could be made to produce more hydrogen gas in total and explain your choice.

[2]

Key Concepts

Explaining rates

Question 3d

Marks: 2

d)

Suggest why it is often better to study a slower reaction instead of a faster one.

[2]

Key Concepts

Rate experiments

Question 4a

Marks: 1

a)

The following energy profile diagram shows the pathways for both a catalysed and uncatalysed reversible reaction:

Identify the letter(s) representing the activation energy for the catalysed reverse reaction.

[1]

Key Concepts

Energy profiles & catalysis

Question 4b

Marks: 2

b)

State and explain the effect that this catalyst will have on the equilibrium yield.

[2]

Key Concepts

How catalysts work

Question 4c

Marks: 2

c)

Vehicles with combustion engines usually have catalytic convertors added to catalyse the oxidation of carbon monoxide into carbon dioxide and to catalyse the reduction of nitrogen oxides to nitrogen. These catalysts are usually rhodium or platinum.

Leaded fuels were phased out as they were found to poison these catalysts, binding irreversibly to the metal surface.

Explain the problems for drivers of the catalysts being poisoned.

[2]

Key Concepts

How catalysts work

Question 4d

Marks: 1

d)

Suggest a situation in which using a catalyst would not be appropriate.

[1]

Key Concepts

How catalysts work

DP IB Chemistry: SL

Topic Questions

6.1 Chemical Kinetics

Question 1a

Key Concepts

Question 1b

Key Concepts

Question 1c

Key Concepts

Question 1d

Key Concepts

Question 2a

Key Concepts

Question 2b

Key Concepts

Question 2c

Key Concepts

Question 2d

Key Concepts

Question 3a

Key Concepts

Question 3b

Key Concepts

Question 3c

Key Concepts

Question 3d

Key Concepts

Question 4a

Key Concepts

Question 4b

Key Concepts

Question 4c

Key Concepts

Question 4d

Key Concepts

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