2.5 The Halogens

Question 0

What is the trend in electronegativity in group 7? Why?

Answer 0

Electronegativity decreases down the group.
Because down the group, the atoms are larger, so:
• shared electrons are further from positively charged nucleus ➡️ weaker forces of attraction.
• + shielding

Question 1

What is the trend in the size of atoms in group 7? Why?

Answer 1

The atoms increase in size down the group.

Because there is an extra shell going down each period.

Question 2

What is the trend in melting/boiling points in Group 7? Why?

Answer 2

Melting/boiling point increases down group 7.

Because down group = larger atoms ➡️ more electrons ➡️ stronger Van der Waal’s forces between molecules

Question 3

What happens to oxidising ability going down the group?

Answer 3

The oxidising ability of the halogens decreases down the group.
(Because less and less electronegative down the group)

Question 4

Equation for extraction of bromine from sea water

Answer 4

Cl2(aq) + 2Br-(aq) ➡️ Br2 + 2Cl-(aq)

Question 5

What happens in displacement reactions? (In the context of halogens)

Answer 5

When halogens are more reactive than the halide in metal halide compound, the halogen will displace the halide.
If the halogens are less reactive, no reaction occurs.

Question 6

What happens when Chlorine reacts with Aluminium Iodide?

Answer 6

Aluminium Chloride will be formed, as well as iodine.

Question 7

What type of reaction occurs between Sodium Iodide and Bromine?

Answer 7

Displacement reaction

Question 8

Are halide ions better reducing agents or oxidising agents? Why?

Answer 8

Halide ions are good reducing agents.

They gain an electron to become halogen molecules, and are therefore electron donors.

Question 9

What type of reaction takes place between Sodium chloride and concentrated sulfuric acid?

Answer 9

An acid-base reaction.

Question 10

Why do you add dilute nitric acid when testing for halide ions?

Answer 10

To rid of any soluble carbonate or hydroxide impurities. These impurities would form insoluble silver carbonate/silver hydroxide.

Question 11

The formation of a ________ coloured precipitate would indicate the presence of chloride ions.

Answer 11

white

Question 12

The presence of ___________ ions means that a cream precipitate is formed when silver nitrate is added.

Answer 12

bromide

Question 13

What is the test to differentiate between halide ions?

Answer 13

The addition of Silver Nitrate.

Question 14

Silver chloride ions dissolve in what?

Answer 14

Dilute ammonia

Question 15

What test would differentiate between silver bromide and silver iodide? What would the results be?

Answer 15

The addition of concentrated ammonia.

Silver iodide is insoluble in concentrated ammonia, whereas silver bromide dissolves in concentrated ammonia.

Question 16

What is the name of the reaction between chlorine and water?

Answer 16

A reversible reaction

Question 17

What is the name of the reaction between chlorine and sodium hydroxide?

Answer 17

A disproportionation reaction.