(a)

(i)

Catalysts can be heterogeneous or homogeneous.

Explain what is meant by a homogeneous catalyst.

[ 1 ]

(ii)

Complete the table by placing one tick $(\checkmark)$ in each row to indicate the mode of action of the catalyst in each reaction.

[ 1 ]

(a)

Nitrous oxide, $\mathrm{N}_{2} \mathrm{O}$ , decomposes into its elements.

2 \mathrm{~N}_{2} \mathrm{O}(\mathrm{~g}) \rightarrow 2 \mathrm{~N}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})

At a high temperature, a small amount of platinum wire is added to a large amount of nitrous oxide. The reaction follows zero order kinetics. The platinum wire behaves as a catalyst.

[ 5 ]

(i)

Sketch a graph, on the axes below, of reaction rate against time for the catalysed decomposition of $\mathrm{N}_{2} \mathrm{O}$ under these conditions.

[ 1 ]

(ii)

Sketch a graph, on the axes below, of $\left[\mathrm{N}_{2} \mathrm{O}\right]$ against time for this reaction.

[ 1 ]

(iii)

Platinum behaves as a heterogeneous catalyst in this reaction.

Describe the mode of action of a heterogeneous catalyst.

[ 3 ]

(a)

Manganese(IV) oxide, $\mathrm{MnO}_{2}$ , acts as a heterogeneous catalyst in the decomposition of hydrogen peroxide, $\mathrm{H}_{2} \mathrm{O}_{2}$ .

[ 4 ]

(i)

Explain what is meant by a heterogeneous catalyst.

[ 1 ]

(ii)

Describe the mode of action of a heterogeneous catalyst in a reaction.

[ 3 ]

(a)

(i)

Explain what is meant by the following terms:
homogeneous catalyst
heterogeneous catalyst

[ 1 ]

(ii)

Iodide ions react with peroxydisulfate ions.

2 \mathrm{I}^{-}+\mathrm{S}_{2} \mathrm{O}_{8}^{2-} \rightarrow \mathrm{I}_{2}+2 \mathrm{SO}_{4}^{2-}

This reaction is slow, but it is catalysed by $\mathrm{Fe}^{2+}$ ions.
Write two equations to explain how this reaction is catalysed by $\mathrm{Fe}^{2+}$ ions.
1

2

[ 2 ]

(iii)

Suggest why the alternative route in the presence of $\mathrm{Fe}^{2+}$ ions has a lower activation energy than the route in the absence of a catalyst.

[ 1 ]

(a)

(i)

Explain what is meant by the following terms:
homogeneous catalyst
heterogeneous catalyst

[ 1 ]

(ii)

Iodide ions react with peroxydisulfate ions.

2 \mathrm{I}^{-}+\mathrm{S}_{2} \mathrm{O}_{8}^{2-} \rightarrow \mathrm{I}_{2}+2 \mathrm{SO}_{4}^{2-}

This reaction is slow, but it is catalysed by $\mathrm{Fe}^{2+}$ ions.
Write two equations to explain how this reaction is catalysed by $\mathrm{Fe}^{2+}$ ions.
1

2

[ 2 ]

(iii)

Suggest why the alternative route in the presence of $\mathrm{Fe}^{2+}$ ions has a lower activation energy than the route in the absence of a catalyst.

[ 1 ]

[Maximum number: 2]

Hypophosphorous acid is an inorganic acid.
The conjugate base of hypophosphorous acid is $\mathrm{H}_{2} \mathrm{PO}_{2}^{-}$ .

(a)

A student suggests that the reaction between $\mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})$ and $\mathrm{OH}^{-}(\mathrm{aq})$ might happen more quickly in the presence of a heterogeneous catalyst.

Describe the mode of action of a heterogeneous catalyst.

[ 2 ]

[Maximum number: 1]

Elements and their compounds are important as catalysts.
In which process is a compound used, rather than an element?

A

catalytic converters

B

Contact process

C

Haber process

D

hydrogenation of alkenes

(a)

The reaction between $\mathrm{S}_{2} \mathrm{O}_{8}{ }^{2-}(\mathrm{aq})$ and $\mathrm{I}^{-}(\mathrm{aq})$ is catalysed by adding a few drops of $\mathrm{Fe}^{3+}(\mathrm{aq})$ .

[ 2 ]

(i)

Use equations to show the catalytic role of $\mathrm{Fe}^{3+}$ in this reaction.

[ 2 ]

(b)

When aqueous solutions of $\mathrm{S}_{2} \mathrm{O}_{8}{ }^{2-}$ and tartrate ions are mixed the reaction proceeds very slowly. However, this reaction proceeds quickly in the presence of an $\mathrm{Fe}^{3+}(\mathrm{aq})$ catalyst. The overall equation for this reaction is shown.
tartrate ions

[ 1 ]

(i)

Suggest why this reaction is slow without the $\mathrm{Fe}^{3+}$ catalyst.

[ 1 ]

[Maximum number: 4]

Iron has atomic number 26.

(a)

$\mathrm{Fe}^{3+}$ can act as a homogeneous catalyst in the reaction between peroxodisulfate ions $\left(\mathrm{S}_{2} \mathrm{O}_{8}{ }^{2-}\right)$ and iodide ions.

[ 4 ]

(i)

What is meant by a homogeneous catalyst?

[ 1 ]

(ii)

Suggest why, in the absence of a catalyst, the activation energy for this reaction is high.

[ 1 ]

(iii)

Write two equations to show how $\mathrm{Fe}^{3+}(\mathrm{aq})$ ions can catalyse the reaction between $\mathrm{S}_{2} \mathrm{O}_{8}{ }^{2-}(\mathrm{aq})$ ions and $\mathrm{I}^{-}(\mathrm{aq})$ ions.
equation 1 equation 2

[ 2 ]

(a)

(i)

Explain the difference between heterogeneous and homogeneous catalysts.

[ 1 ]

(ii)

Complete the table using ticks $(\checkmark)$ to indicate whether the catalyst used in the reaction is heterogeneous or homogeneous.

[ 2 ]