3.2.3 Group 7 (halogens)

Question 1

What general trend in electronegativity occurs down Group 7 from fluorine to iodine?

Answer 1

Decreases

Increased atomic radius and shielding reduce the nucleus’ attraction for bonding electrons.

Question 2

What happens to the boiling point of halogens as you move down Group 7?

Answer 2

Increases

Larger molecules have stronger London dispersion forces.

Question 3

Fill in the blank:

The increase in boiling point down the halogen group is due to stronger _______ forces.

Answer 3

van der Waals

These induced dipole–dipole forces increase with molecular size.

Question 4

True or False:

Chlorine is a stronger oxidising agent than iodine.

Answer 4

True

Oxidising ability decreases down the group.

Question 5

What happens to the oxidising ability of halogens down Group 7?

Answer 5

Decreases

Larger atoms gain electrons less easily.

Question 6

True or False:

Iodide ions are stronger reducing agents than chloride ions.

Answer 6

True

Reducing ability of halide ions increases down the group.

Question 7

Fill in the blank:

In displacement reactions, a more reactive halogen will _______ a less reactive halide from solution.

Answer 7

displace

For example, Cl₂ displaces Br^- from solution.

Question 8

What reagent is used to test for halide ions in aqueous solution?

Answer 8

Acidified silver nitrate

It forms characteristic precipitates with halide ions.

Question 9

True or False:

Silver nitrate solution is acidified to remove interfering carbonate ions.

Answer 9

True

Nitric acid prevents false positives from other precipitates.

Question 10

Fill in the blank:

A white precipitate formed with silver nitrate indicates the presence of _______ ions.

Answer 10

chloride

AgCl forms a white precipitate.

Question 11

What happens when dilute ammonia is added to silver chloride?

Answer 11

Dissolves

AgCl dissolves because it forms a soluble complex ion.

Question 12

Which silver halide does not dissolve in ammonia solution?

Answer 12

Silver iodide

AgI is the least soluble of the silver halides.

Question 13

What ions are formed when chlorine reacts with water in the main equilibrium reaction?

Answer 13

Chloride and chlorate(I)

Cl₂ + H₂O ⇌ Cl^- + ClO^- + H⁺.

Question 14

What type of ion is ClO⁻ formed when chlorine reacts with water?

Answer 14

Chlorate(I) ion

Also known as the hypochlorite ion.

Question 15

Fill in the blank:

When chlorine dissolves in water, it forms chloride ions and _______ (I) ions.

Answer 15

chlorate

These ions contribute to chlorine’s disinfectant properties.

Question 16

True or False:

Chlorine can react with water to produce oxygen and chloride ions.

Answer 16

True

An alternative reaction forms O₂ and HCl.

Question 17

What is the main use of chlorine in public water supplies?

Answer 17

To kill bacteria.

Chlorine kills bacteria and other microorganisms.

Question 18

True or False:

The health benefits of chlorinating drinking water generally outweigh the risks.

Answer 18

True

Chlorination has greatly reduced waterborne diseases.

Question 19

Fill in the blank:

Chlorine reacts with cold dilute sodium hydroxide to form sodium chloride and sodium _______ (I).

Answer 19

chlorate

The product is sodium chlorate(I) (sodium hypochlorite).

Question 20

What common household chemical contains sodium chlorate(I)?

Answer 20

Bleach

Sodium hypochlorite is widely used as a disinfectant and bleaching agent.

Question 21

True or False:

Chlorate(I) ions act as oxidising agents in disinfectants.

Answer 21

True

They kill microbes by oxidising biological molecules.

Question 22

Why is chlorine effective in killing bacteria in water treatment?

Answer 22

Strong oxidising agent

It disrupts essential cellular components in microorganisms.

Question 23

Fill in the blank:

In water treatment, chlorine is added because it kills harmful _______.

Answer 23

microorganisms

This prevents diseases such as cholera and typhoid.

Question 24

What societal factor must be considered when adding chemicals like chlorine to water supplies?

Answer 24

Risk–benefit balance

Decisions weigh health benefits against potential chemical risks.

Question 25

Explain **why the electronegativity** of the halogens **decreases** going down the group

Answer 25

The number of electron shells increases down the group. This increases atomic radius and electron shielding. As a result, the nucleus has a weaker attraction for bonding electrons.

Question 26

What is the colour of the **silver bromide precipitate**?

Answer 26

Cream

Question 27

What is the colour of the **silver iodide precipitate**?

Answer 27

Yellow

Question 28

How does **NaCl react with concentrated H₂SO₄**?

Answer 28

Forms HCl gas. This is an acid-base reaction only, no redox occurs.

Question 29

How does **NaBr** react with concentrated **H₂SO₄**?

Answer 29

Forms **HBr** gas. **HBr** can be oxidized by **H₂SO₄** to produce **Br₂**. ## Footnote This occurs because **Br⁻** is a stronger reducing agent than **Cl⁻**.

Question 30

How does **NaI** react with concentrated **H₂SO₄**?

Answer 30

Forms **HI** gas. **HI** is a strong reducing agent, leading to further reactions that can produce: * **I₂** (iodine) * **H₂S**, **SO₂**, or **S** (depending on conditions)

Question 31

Why do **larger halide ions** have **stronger reducing ability**?

Answer 31

Larger ions (I⁻, Br⁻) have weaker hold on their electrons, making them more able to donate electrons → stronger reducing agents → more likely to reduce H₂SO₄