2.15 understand these displacement reactions as redox reactions.

When a more reactive halogen displaces a less reactive one this is a redox reaction.

This means that one element has been reduced (gained electrons) and one has been oxidised (lost electrons.)

Helpful hint!

Oilrig helps to remind you how redox reactions go:

Oxidation

Is

Loss

Reduction

Is

Gain

2.14 describe experiments to demonstrate that a more reactive halogen will displace a less reactive halogen from a solution of one of its salts

A more reactive halogen will displace a less reactive one that is bonded as a salt. This will only happen if the salt is dissolved in water or a gas.

This page has a really good example:
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/patterns/groupsrev5.shtml

2.12 explain, in terms of dissociation, why hydrogen chloride is acidic in water but not in methylbenzene

Water (H2O) is a polar molecule.

Methylbenzene is a non-polar molecule.

Hydrogen chloride is a polar molecule.

Polars only dissolve in polars.

When hydrogen chloride is dissolved you get +H ions.

These are acidic.

2.13 describe the relative reactivities of the elements in Group 7

Group 7 elements become less reactive as you go down the group.

At the top, the positive charge of the proton in the nucleus is close to the surface (as there are few shells) this makes it easy for them to pull in the one electron they need to become stable, meaning they are very reactive.

Lower down where there are more shells the pull of the proton is further from the surface making it less easy to pull in another electron.

2.11 understand the difference between hydrogen chloride gas and hydrochloric acid

Hydrogen chloride gas is HCl

Hydrochloric acid is hydrogen chloride dissolved in water. The two ions become detached leaving Cl- and H+ ions. H+ is acidic, hence the term acid.

2.10 make predictions about the properties of other halogens in this group

We would expect the colour to keep getting darker and the melting and boiling points to keep getting higher further down the group.

2.9 recall the colours and physical states of the elements at room temperature

Fluorine.............. Gas........... yellow
Chlorine............. Gas........... yellow-green
Bromine............. Liquid........ red-brown
Iodine................ Solid.......... purple
Astatine............. Solid.......... black