Types of Catalysis

Question 1

What are the three main types of catalysis?

Answer 1

Homogenous catalysis
Heterogeneous catalysis
Autocatalysis

Question 2

Define homogenous catalysis

Answer 2

A catalysis in which both the reactants and the catalyst are in the same phase

Question 3

Define a phase.

Answer 3

A specific state of matter that has uniform chemical and physical properties

Question 4

What is an example of homogeneous catalysis?

Answer 4

The ‘iodine snake’/ the reaction between concentrated potassium iodide solution and hydrogen peroxide solution

Question 5

Why is the ‘iodine snake’ considered a homogenous catalysis?

Answer 5

As both liquids are in the same phase

Question 6

Define heterogeneous catalysis.

Answer 6

Catalysis in which the reactants and the catalyst are in different phases

Question 7

What is an example of heterogeneous catalysis?

Answer 7

The reaction between methanol vapour and oxygen gas to form methanal using platinum as the catalyst

Question 8

Describe the 9 steps in the reaction between methanol vapour and oxygen gas using platinum as a catalyst to form methanal

Answer 8

1. 25 cm cubed of methanol is placed in a conical flask
2. A piece of cardboards in the shape of a ‘T’ is covered in aluminium foil and suspended in the conical flask
3. The methanol is heated to 60 degrees Celsius in a fume cupboard and is then placed on a heat resistant mat
4. A spiral of platinum wire is heated until red hot over a Bunsen burner using tongs
5. The hot spiral of platinum wire is quickly hung inside the conical flask
6. The platinum now undergoes a cycle of glowing red hot and cooling again as the reaction proceeds
7. ‘Pops’ will be heard as one of the products, hydrogen explodes
8. The smell of methanal will be noticed
9. A flame may be observed in the flask

Question 9

Why is the T covered in aluminium foil during the reaction between methanol vapour and oxygen gas using platinum as a catalyst to form methanal?

Answer 9

To prevent the cardboard from burning

Question 10

Why does the platinum glow during the reaction between methanol vapour and oxygen gas using platinum as a catalyst to form methanal?

Answer 10

The platinum glows as the reaction taking place is exothermic (gives out heat)

Question 11

Why will the platinum cease to glow for a while before becoming red hot again during the reaction between methanol vapour and oxygen gas using platinum as a catalyst to form methanal?

Answer 11

This occurs as carbon monoxide is formed due to incomplete combustion of the methanol which poisons the catalyst but once this gas leaves the platinum it will begin to glow again

Question 12

What causes the flame inside the conical flask during the reaction between methanol vapour and oxygen gas using platinum as a catalyst to form methanal?

Answer 12

The hot wire igniting the methanol vapour causes the flame

Question 13

What extinguishes the flame which may form as a result of the methanol igniting during the reaction between methanol vapour and oxygen gas using platinum as a catalyst to form methanal?

Answer 13

When the flame uses up the oxygen in the flask the flame will be extinguished

Question 14

What happens to methanol in the absence of sufficient oxygen?

Answer 14

Methanol oxidises to methanal and hydrogen gas

Question 15

Define autocatalysis

Answer 15

Catalysis in which one of the products of the reaction act as a catalyst for the reaction

Question 16

Describe the rate of reaction throughout an autocatalytic reaction.

Answer 16

An autocatalytic reaction starts slowly but speeds up as the catalyst product starts to form

Question 17

Give an example of an autocatalytic reaction.

Answer 17

The reduction of manganate (VII) ions

Question 18

How is the reduction of manganate (VII) ions autocatalytic?

Answer 18

As when the first few drops of the purple MNO4- solution are added to the Fe2+ solution they are decolourised slowly but subsequent drops are decolourised rapidly i.e. the Mn2+ formed by the initial slow reaction catalyses the subsequent reaction