Group 7- The Halogens UNIT 2

Question 0

The boiling points of the halogens ……….. down the group

Answer 0

Increase

Due to increasing strength of vdw forces as the size and relative mass of the atoms increases.

Question 1

What are the halogens

Answer 1

The highly reactive non metals in group 7

Question 2

Electronegativity ……….. down the group

Answer 2

Decreases

As you go down the larger the atom becomes. The larger atoms attract electrons less than smaller ones

Question 3

What happens when halogens react

Answer 3

They gain an electron. They get less reactive down the group as the atoms get larger. So they become less oxidising down the group

Question 4

When will a halogen displace a halide from solution

Answer 4

If the halide is below it in the periodic table

Question 5

What happens if you mix chorine gas with dilute sodium hydroxide at room temp

Answer 5

Forms sodium chlorate solution, which is bleach

Question 6

What is disproportionation

Answer 6

When the oxidation state of an element goes both up and down

Question 7

Uses for sodium chlorate solution

Answer 7

Water treatment, to bleach paper and textiles

Question 8

What happens when you mix chlorine with water

Answer 8

It undergoes disproportionation
You end up with a mixture of HCl and chloric acid. Aqueous chloric acid ionises to make chlorate ions. These ions kill the bacteria

Question 9

Why is chlorine an important part of water treatment

Answer 9

Kills disease causing microorganisms

Some chlorine persists in water and prevents reinfection further down the supply

Prevents the growth of algae, eliminating bad tastes and smells, removes discolouration caused by organic compounds

Question 10

Risks of using chlorine in water treatment

Answer 10

Chlorine gas is very harmful if it’s breathed in, it irritates respiratory system. Liquid chlorine on the skin or eyes causes severe chemical burns

Water contains a variety of organic compounds eg from the decomposition of plants. Chlorine reacts with these compounds to form chlorinated hydrocarbons, many of these are carcinogenic (cancer causing). However this increased cancer risk is small compared to the risks from untreated water

Question 11

What are ethical issues with using chlorine in water treatment

Answer 11

We don’t get a choice about having our water chlorinated, some people object to this as forced ‘mass medication’