Halogens

Question 0

What are the melting and boiling points like?

Answer 0

Halogens have low melting and boiling points, which increase as you go down the table.

Question 1

What states are they?

Answer 1

Fluoride and chlorine are gases, bromine is a liquid, iodine and astatine are solids.

Question 2

Describe the reactivity

Answer 2

Reactivity decreases as you go down the group. Fluorine is very reactive. This is shown by the displacements tests.

Question 3

Describe and explain the displacement reaction

Answer 3

You add one of the halogens to a halogen salt. The less reactive halogen will be ‘kicked out’ by the other one. E.g. Chlorine + sodium bromide => bromine + sodium chloride
This is a redox reaction. The bromine loses electrons and the chlorine gains electrons

Question 4

What are the colours of the halogens?

Answer 4

They get darker as you go down the group.
Fluorine pale yellow
Chlorine yellow-green
Bromine red brown. Bromine water oranges
Iodine grey, turn to a dark purple vapour when warmed

Question 5

What’s the difference between hydrogen chloride gas and hydrochloride acid?

Answer 5

• HCl is the gas
• when in gas, the H atoms can’t disaccociate from the molecule ∴ no H+ atoms, so doesn’t behave like acid
• in aqueos form, H atoms can disassociate from molecules ∴ H+ atoms present ∴ behave like an acid

Question 6

Why’s hydrogen chloride acidic in water but not methylbenzene?

Answer 6

• hydrogen chloride is a polar molecule, and they can only disassociate in other polar molecules
• water is polar, methylbenzene isn’t
• when HCl is dissolved in H₂O you get H+ ions = acidic

Question 7

What are the uses of some of the halogens?

Answer 7

Cl- sterilising water
Br- pesticides and plastics
I- sterilising wounds