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 in a solution of its salt but only if the salt is dissolved in water or a gas.

Eg. if chlorine (Cl) is added to a solution of sodium bromide, it will form a solution of sodium chloride instead, and bromine will become a 'waste' product.

The balanced equation would be:

Cl₂ + 2NaBr → 2NaCl + Br₂

2.13 Describe the relative reactivities of the elements in Group 7

The further down the group you go, the less reactive the substance (note that astatine is radioactive and very rare....)

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

See also 2.11

Basically, the ions dissociate (split up) into Cl^- and H⁺ , making it acidic because of the H⁺ ions. This only happens in water.

In methylbenzene, the ions do not dissociate, and so hydrogen chloride does NOT become acidic ^_^

2.11 Understand the difference between hydrogen chloride gas and hydrochloric acid

Hydrogen chloride gas is HCl_(g)
When dissolved in water, it becomes HCl_(aq) because the ions become detached: they dissociate, leaving separate H⁺ and Cl^- ions. H⁺ is acidic, which is what makes it an acid :)

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

As you go down the group:

• Reactivity decreases
• Color darkens
• Melting/boiling point increases
• Particles become closer together (i.e. fluorine is a gas but astatine is a solid)

Figure 1: Fluorine at room temperature, in a bottle (it is a highly toxic gas after all!)

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

Fluorine (F)

• Gas
• Yellow

Chlorine (Cl)

• Gas
• Yellow-green

Bromine (Br)

• Liquid
• Brownish red

Iodine (I)

• Solid
• Purple

Astatine (At)

• Solid
• Black