10 - The Halogens

Question 1

What are the Group 7 elements?

Answer 1

Non-metals that exist as diatomic molecules.

Question 2

What is the colour and state of fluorine at room temperature?

Answer 2

Pale yellow gas

Question 3

What is the colour and state of chlorine at room temperature?

Answer 3

Greenish gas.

Question 4

What is the colour and state of bromine at room temperature?

Answer 4

Red-brown liquid.

Question 5

What is the colour and state of iodine at room temperature?

Answer 5

Black solid.

Question 6

What is the trend in atomic radius down Group 7?

Answer 6

Increases
As each element will have an extra filled layer of electrons, increasing shielding.

Question 7

What is the trend in melting/boiling points down Group 7?

Answer 7

Increases
As the larger the atom the greater the electron density so the stronger the van der Waal’s forces between molecules.

Question 8

Why are fluorine’s properties untypical?

Answer 8

The F-F bond is weak compared to the other halogens as the small size of fluorine atom leads to repulsion between the non-bonding electrons.

Question 9

What is electronegativity?

Answer 9

A measure of the ability of an atom to attract electron density towards itself within a covalent bond.

Question 10

What is the trend in electronegativity down Group 7?

Answer 10

Decreases
As the larger the atom the further the shared electrons are from the hydrogen nucleus therefore the greater the shielding so the atom attracts the shared electrons less.

Question 11

How do halogens react?

Answer 11

They gain electrons to form -1 ions.
They are oxidising agents and are reduced.

Question 12

What is the trend in oxidising ability down Group 7?

Answer 12

Decrease
As the larger the atom the harder it is to attract an electron due to greater shielding.

Question 13

How do halogens react with metal halides in solution?

Answer 13

The halide in the compound will be displaced by only a more reactive halogen.

Question 14

What is the trend in reactivity down Group 7?

Answer 14

Decrease
As the larger the atom the greater the shielding so the ability to attract an electron decreases.

Question 15

Can halide ions act as reducing agents?

Answer 15

Yes as they can lose electrons (oxidise) and become halogen molecules.

Question 16

What is the trend in reducing power down Group 7?

Answer 16

Increases
As the atoms get larger the valence electron gets further away from the nucleus therefore it is easier to remove the outer electron.

Question 17

What does solid sodium chloride and concentrated sulphuric acid produce?

Answer 17

Sodium hydrogen sulphate (NaHSO4(s))
Hydrogen chloride (HCl(g))

Question 18

Why is the reaction between solid sodium chloride + conc. sulphuric acid not redox?

Answer 18

Its only an acid-base reaction as the Cl- ions are too weak a reducing agent to reduce the sulphur (SO4^-2).

Question 19

What does solid sodium bromide and concentrated sulphuric acid produce at first?

Answer 19

Sodium hydrogen sulphate (NaHSO4(s))
Hydrogen bromide (HBr(g))
Acid-base reaction

Question 20

What does hydrogen bromide and concentrated sulphuric acid produce second?

Answer 20

Sulphur dioxide
Bromine
Water

Question 21

Why does sodium bromide + sulphuric acid produce a redox reaction?

Answer 21

Br- is a strong reducing agent so can reduce sulphuric acid to sulphur dioxide.

Question 22

What does solid sodium iodide and concentrated sulphuric acid produce at first?

Answer 22

Sodium hydrogen sulphate (NaHSO4(s))
Hydrogen iodide (HI(g))
Acid-base reaction

Question 23

What does hydrogen iodide and concentrated sulphuric acid produce second?

Answer 23

Hydrogen sulphide (H2S)
Iodine (s)
Water

Question 24

Why does sodium iodide + sulphuric acid produce a redox reaction?

Answer 24

I- is a strong reducing agent so it reduces sulphuric acid to hydrogen sulphide.

Question 25

How can we identify metal halides with silver ions?

Answer 25

1) Add dilute nitric acid to remove any soluble carbonate/ hydroxide impurities.
2) Add a few drops of silver nitrate solution and a precipitate forms
Ag+(aq) + X-(aq) –> AgX(s)

Question 26

In the test for metal halides with silver ions why is nitric acid added?

Answer 26

To remove impurities that would have formed silver carbonate/ hydroxide which are indistinguishable solids.

Question 27

What halide can the silver ion test not be used for and why?

Answer 27

Fluoride
It doesn’t form a precipitate as it is soluble in water.

Question 28

How can the silver halide precipitate be identified?

Answer 28

AgCl - white ppt - soluble in dilute ammonia
AgBr - cream ppt - soluble in concentrated ammonia.
AgI - pale yellow ppt - insoluble in concentrated ammonia.

Question 29

Why is chloric acid used in pools?

Answer 29

Kills bacteria via oxidation.

Question 30

What does the reaction between chlorine and water form?

Answer 30

Chloric acid (HClO)
Hydrochloric acid

Question 31

What is the trend in the reaction of the halogens with water down Group 7?

Answer 31

Reacts with decreasing vigour.

Question 32

What is the reaction between chlorine and water in sunlight?

Answer 32

Forms: HCl + O2
Leads to dichlorination of pools.

Question 33

What does chlorine + cold aqueous sodium hydroxide form?

Answer 33

Water
Sodium chloride -NaCl
Sodium chlorate(I) - NaOCl - which is an active ingredient in bleach.