Disproportionation and Water Treatment

Question 1

What type of element undergoes disproportionation?

Answer 1

Halogens

Question 2

What type of alkali solution do halogens react with?

Answer 2

Cold, dilute alkali solutions.

Question 3

Is the halogen oxidised or reduced?

Answer 3

It is both oxidised and reduced.

Question 4

What is meant by a disproportionation reaction?

Answer 4

This is where an element is both oxidised and reduced.

Question 5

What two elements/compounds are used to make bleach?

Answer 5

Chlorine and sodium hydroxide.

Question 6

What is the chemical name for bleach?

Answer 6

Sodium chlorate (1) solution.

Question 7

What are 4 uses of sodium chlorate (1) solution?

Answer 7

Water treatment
Bleaching textiles
Bleaching paper
Toilets

Question 8

What happens when you mix chlorine, iodine or bromine with water?

Answer 8

It undergoes a disproportionation reaction.

Question 9

What is chorine used for?

Answer 9

It is used to kill bacteria in water.

Question 10

What products are formed from mixing water?

Answer 10

Hydrochloric acid and chloric (1) acid.

Question 11

Which chlorine containing acid ionises?

Answer 11

Aqueous chlorate (1) acid

Question 12

What does aqueous chlorate (1) acid ionise to?

Answer 12

Chlorate (1) ions

Question 13

What kills bacteria?

Answer 13

Chlorate (1) ions

Question 14

Why is chlorine an important part of water treatment?

Answer 14

It kills disease-causing microorganisms and prevents reinfection further down the water supply.
It also prevents the growth of algae.

Question 15

Why is it important that algae is not present in the water supply?

Answer 15

It can cause discolouration and can create bad tastes and smells.

Question 16

What is the problem with chlorine gas?

Answer 16

It irritates the respiratory system if breathed in.

Question 17

What is the problem with liquid chlorine?

Answer 17

If it gets in eyes or skin it can cause severe chemical burns.

Question 18

What else does water contain?

Answer 18

A variety of hydrocarbons.

Question 19

What products are formed from the reaction of chlorine with organic hydrocarbons?

Answer 19

Chlorinated hydrocarbons.

Question 20

What is the problem with chlorinated hydrocarbons?

Answer 20

Some of them are carcinogenic.

Question 21

If chlorine can create carcinogens, why is it used in water treatment?

Answer 21

The increased cancer risk is small especially compared to the risks of untreated water.

Question 22

What are the two alternatives to chlorine in water treatment?

Answer 22

Ozone and UV light.

Question 23

What is ozone good for?

Answer 23

It is good at killing microorganisms.

Question 24

Why is ozone good at killing microorganisms?

Answer 24

It is a strong oxidising agent.

Question 25

What is the chemical formulae for ozone?

Answer 25

O3

Question 26

How does UV kill microorganisms?

Answer 26

It damages their DNA.

Question 27

What are the two key problems with using ozone in water treatment?

Answer 27

Its expensive and has a short half life so the water treatment isn’t permanent.

Question 28

Where is UV light ineffective?

Answer 28

In cloudy water.

Question 29

What is the other problem with UV light?

Answer 29

It won’t stop the water from being contaminated further down the line.

Question 30

What does UV stand for?

Answer 30

Ultraviolet