Group 7- The Halogens

Question 1

Colour of Fluorine

Normal Physical State

Answer 1

Pale Yellow

Gas

Question 2

Colour of Chlorine

Normal Physical State

Answer 2

Green

Gas

Question 3

Colour of Bromine

Normal Physical State

Answer 3

Red-brown

Liquid

Question 4

Colour of Iodine

Normal Physical State

Answer 4

Grey

Solid

Question 5

Trend in Boiling Points

Explain

Answer 5

Boiling points increase down group 7.

Due to increasing strength of the van der Waals forces as the size and relative mass of the molecules increases.

Trend is shown in the changes of physical state from fluorine (gas) to iodine (solid)

Question 6

Trend in Electronegativity

Explain

Answer 6

Electronegativity decreases down group 7.

Halogens are all highly electronegative elements.

But larger atoms attract electrons less than smaller ones.

Due to the electrons being further from the nucleus and are shielded by more electrons

Question 7

Trend in Reactivity

Explain

Answer 7

Decrease in reactivity down group 7.

Because the atoms are getting larger.

The outer shell is also further away from the nucleus, so the electrons are less strongly attracted to it

Question 8

Oxidising Ability

Where can their relative oxidising strengths be seen?

Answer 8

Halogens become less oxidising down the group.

In their displacement reactions

Question 9

Rule of Displacement in Halogens

Answer 9

A halogen will displace a halide from solution if the halide is below it in the periodic table

Question 10

Making Bleach

Answer 10

Mix chlorine gas with cold, dilute, aqueous sodium hydroxide you get sodium chlorate (I) solution.

This is common household bleach

Question 11

Equation for making bleach

Name of reaction

Explain

Answer 11

2NaOH + Cl2 –> NaClO + NaCl + H2O.

Disproportionation.

Oxidation state of chlorine goes up and down, meaning that chlorine is both oxidised and reduced

Question 12

Three Main Uses of Sodium Chlorate (I) Solution

Answer 12

Used in water treatment

Used to bleach paper

Used to bleach textiles

Question 13

Reaction of Chlorine Mixed with Water

Name of Reaction

Answer 13

Produces a mixture of chloride ions and chlorate (I) ions.

Disproportionation

Question 14

Equation for Reaction of Chlorine mixed with Water

Answer 14

Cl2 + H2O <==> 2H+ + Cl- + ClO-

Question 15

Reaction of Chlorine mixed with Water in Sunlight

Answer 15

Chlorine can decompose water to form chloride ions and oxygen

Question 16

Equation for Reaction of Chlorine mixed with Water in Sunlight

Answer 16

2Cl2 + 2H2O <==> 4H+ + 4Cl- + O2

Question 17

Uses of Chlorate (I) Ions

Answer 17

Kills bacteria.

When adding chlorine (or a compound containing chlorate I ions) to water it can make it safe to drink or swim in

Question 18

Three Strengths of adding Chlorine to Drinking Water

Answer 18

1. It kills disease-causing microorganisms.
2. Some chlorine persists in the water and prevents reinfection further down the supply.
3. It prevents the growth of algae, eliminating bad tastes and smells, and removes discolouration caused by organic compounds

Question 19

Two Limitations of adding Chlorine to Drinking Water

Answer 19

1. Chlorine gas is very harmful if it’s breathed in- it irritates the respiratory system.
   Liquid chlorine on skin or eyes causes severe chemical burns.
   Accidents involving chlorine could be very serious or fatal.
2. Water contains a variety of organic compounds that chlorine can react with to form chlorinated hydrocarbons (eg chloromethane) and many of these chlorinated hydrocarbons are carcinogenic.
   However, increased cancer risk is small compared to the risks from untreated water