MC test: Catalysts

Multiple choice quiz on A.3 Catalysts

Use the following 'quiz' to test your knowledge and understanding of this sub-topic. As this relates to a sub-topic on the options you may need access to the IB data booklet.

If you get an answer wrong, read through the explanation carefully to learn from your mistakes.

Which are the three main elements present in all naturally occurring zeolites?

Naturally occurring zeolites are aluminosilicate compounds

 

Which acts as a homogeneous catalyst?

In the esterification reaction the products, reactants and catalyst are all in the same (liquid/aqueous) phase. The other three reactions involve gases reacting in the presence of a solid heterogeneous catalyst.

 

Which are true statements about catalysts?

I. They can change chemically during a reaction.

II. They provide an alternative pathway for the reaction with a lower activation energy.

III. They may be poisoned by substances that affect their active site

Catalysts are chemically unchanged at the end of the reaction but they may change chemically during the reaction.

 

Which are advantages when embedded platinum atoms in a carbon nanotube are used as a catalyst rather than a piece of platinum metal?

I. Less platinum is required to catalyse the reaction.

II. The standard enthalpy change for the reaction is lowered.

III. The surface area of the catalyst per unit mass is greater.

Because the surface area of the catalyst available to the reactants is increased by a large factor less platinum (which is expensive) is required. Using a catalyst provides a reaction pathway with a lower activation energy but the overall enthalpy change for the reaction remains unchanged. 

 

Which statement is true about all gaseous reactions when they are catalysed by a solid catalyst?

Reactant particles are adsorbed (not absorbed) onto the surface of heterogeneous catalysts. Catalysts have no affect on the position of equilibrium and since no reaction intermediates are formed with heterogeneous catalysts there is no change in oxidation state.

 

Which factors help to explain why transition metals and their compounds tend to be good catalysts?

I. Transition metals can form complexes with carbon monoxide and with cyanide ions.

II. Transition metals are able to adsorb gases onto their surface.

III. Transition metals exhibit variable oxidation states.

The metals themselves tend to be good heterogeneous catalysts as they can adsorb reactant gases on their surface and the complexes tend to be good homogeneous catalysts as they can form temporary activated complexes or reaction intermediates which involves a change in oxidation state. Cyanide ions and carbon monoxide poison catalysts by blocking their active site.

 

Which factors affect the choice of a suitable catalyst in industry?

I. Selectivity

II. Cost to benefit ratio

III. Environmental impact

All three are important factors to be considered.

 

Two different reactions to produce oxygen are:

1. Adding solid manganese(IV) oxide to hydrogen peroxide.

2. Adding an acidified solution of potassium manganate(VII) to hydrogen peroxide. 

Which is a correct statement?

MnO2 catalyses the decomposition of hydrogen peroxide. During the heterogeneous reaction the oxidation state of oxygen changes from −1 in H2O2 to 0 in oxygen gas and −2 in water, whereas the oxidation state of Mn is unchanged at the end of the reaction. In the redox reaction between acidified potassium manganate(VII) solution and hydrogen peroxide the oxidation state of Mn changes from +7 in MnO4− to +2 in Mn2+.

 

The suggested two-step mechanism for the reaction between nitrogen dioxide and carbon monoxide below 775 K to form nitrogen monoxide and carbon dioxide is:

Step 1: 2NO2(g)  → NO(g) + NO3(g)

Step 2: NO3(g) + CO(g) → NO2(g) + CO2(g)

Which is a true statement if this mechanism is correct?

The overall equation is NO2(g)  +  CO(g)  → NO(g) + CO2(g) and no catalyst is present. NO3 is a reaction intermediate but it is not a catalyst as there is none present at the start (nor at the end) of the reaction.

 

Other than being used as a catalyst what other major use is made of zeolites?

The ions that cause water to be hard, such as Ca2+ and Mg2+, can be exchanged for ions such as Na+ and H+ ions by passing hard water through zeolites columns or beds to soften the water.

 

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