Halogens

Question 1

Boiling point trend

Answer 1

Decreases down the group
* more electrons down the group
* stronger van der waal forces

Question 2

Reactivity

Answer 2

Decreases down the group
* The acceptance of electron decreases down the group due to:
* Increasing atomic radii
* Decreasing force of attraction
* increasing shieding effect
Flourine is the strongest electron acceptor (oxidising agent)

Question 3

Disproportionation

Chlorine with water, and with sodium hydroxide

Answer 3

This is where chlorine undergos a redox reaction, for example:
* Chlorine is used in water treatment to kill bacteria and make water safe for drinking to form hydrochlroric acid and chloric acid (I):
Cl₂ + H₂O ⇋ HCl + HClO
* Chlorine reacts with cold sodium hydroxide (15°C) to form sodium chloride and sodium chlorate (l)
Cl₂(aq) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H₂O(l)
Bleach is a mixture of sodium chloride and sodium chlorate and kills bacteria
* The chlorate ions oxidises the coloured dyes and other coloured molecules and helps to remove stains.

Question 4

Testing for halides
Table

Answer 4

j

X⁻(aq) + Ag⁺(aq) → AgX (s)

Silver Chloride - white ppt, soluble in dilute ammonia and concentrated ammonia
Silver Bromide - Cream ppt, insoluble in dilute ammonia but soluble in concentrated ammonia
Silver Iodide - ** Yellow ppt, insoluble in dilute and concentrated ammonia

Question 5

Reducing power

Answer 5

To reduce something a halide ion needs to lose an electron from its outer shell. This depends on:
* The attraction between the nucleus and outer electrons
* Shielding
The further down the group the halide is, the easier it is for it to lose an electron and the greater its reducing power

Question 6

What does nitric acid do when testing for halides

Answer 6

Nitric acid can be added first to remove carbonates/hydroxide ions that may give a ppt

Question 7

Reactivity (Colour in cycloheaxane)

Answer 7

Chlorine - Pale green in free halogen solution, Pale yellow in cyclohexane

Bromine - Yellow in free halogen solution, Orange in cyclohexane

Iodine - Brown in free halogen solution, Purplein cyclohexane