2.3 Group 7, the halogens

Question 1

What are the colours and standard states of the 4 main halogens?

Answer 1

Fluorine - pale yellow gas
Chlroine - green gas
Bromine - red-brown liquid
Iodine - black solid

Question 2

Why does fluorine have unexpectally weak diatomic molecules?

Answer 2

The F atoms are very small meaning the repulsive, non bonding pairs are close together

Question 3

What is the general trend for electronegativity down group 7?

Answer 3

Electronegativity decreases down the group with fluorine anomolously high

Question 4

What is the general trend for melting and boiling points down group 7?

Answer 4

They increase down the group as the VdW forces increase the more electrons there is

Question 5

What is the general trend for oxidising power down group 7?

Answer 5

Oxidising power decreases going down the group as the nucleus is further away from the outer energy levels meaning it is harder to gain electrons

Question 6

What is the general trend for displacement reactions of halogens and metal halides?

Answer 6

The elements higher in the group will displace the elements lower down from the metal.

Question 7

What part of a displacement reaction causes the colour of the solution?

Answer 7

The dissolved diatomic molecule, e.g Br₂ will cause a red-brown colour

Question 8

What will the equation and colour change be where sodium iodide reacts with bromine?

Answer 8

Br₂ + 2NaI → I₂ + 2NaBr

Brown-red solution to black solution

Question 9

Write the ionic equation and describe any observations between sodium bromide and chlorine

Answer 9

Cl₂ + 2Br^- → Br₂ + 2Cl^-
Colourless solution to red-brown solution

Question 10

What is the general trend for halogens as reducing agents?

Answer 10

The further down the group you go, the easier it is for the halogen to lose an electron

Question 11

What reaction happens when solid sodium chloride reacts with concentrated sulphuric acid and why?

Answer 11

NaHSO₄(s) and HCl(g) are formed as the chlorine is too weak of a reducing agent to lower the sulphurs +6 oxidation state. The HCl will appear as a colourless gas coming from the reaction.

Question 12

What reactions happens when solid sodium bromide reacts with concentrated sulphuric acid and why?

Answer 12

NaBr + H₂SO₄(l) → NaHSO₄(s) and HBr(g)
2H⁺ + 2Br^- + H₂SO₄(l) → SO₂ + 2H₂O + Br₂
The bromine is a strong enough oxidising agent to reduce the sulphur to sulphur dioxide changing its oxidation state from +6 to +4

Question 13

What are the products of the reaction of solid sodium iodide and concentrated sulphuric acid and why?

Answer 13

1. NaHSO₄(s) and HI(g)
2. SO₂ + 2H₂O + I₂
3. S + 4H₂O + 3I₂
4. H₂S + 4H₂O + 4I₂
   The iodine is a strong enough reducing agent to reduce sulphurs oxidation state from +6 to +4, 0 and -2

Question 14

How can you indentify the sulphur products of the reaction between metal halides and concentrated sulphuric acid?

Answer 14

SO₂ - colourless gas
H₂S - strong, bad egg smell
S - yellow solid

Question 15

Describe the test for halide ions by their precipates and the results for fluorine, chlorine, bromine and iodine

Answer 15

1. Add HCl to remove carbonate ions
2. Add silver nitrate solution to the solution you’re testing
   Fluorine→No precipitate
   Chlorine→White precipitate→Redissolves in dilute ammonia solution
   Bromine→Cream precipitate→Redissolves in concentrated ammonia
   Iodine→Yellow precipitate→Doesn’t redissolve

Question 16

What are the products from the reaction of chlorine and water and what is chlorines oxidation state in each?

Answer 16

Chloric acid, HClO (Cl +1), and hydrochloric acid, HCl (Cl -1)

Question 17

How is chlorine used to keep swimming pools clean and why do pools in direct sunlight need additonal chlorine?

Answer 17

Chloric acid kill bacteria but in direct sunlight the reaction between water and chlorine can form double the about of HCl and oxygen.

Question 18

What are the products and uses of the reaction between chlorine and cold, dilute sodium hydroxide?

Answer 18

NaClO, an active ingredient in bleach, NaCl and H₂O