Group 7

Question 1

What is the trend in boiling point down group 7?

Answer 1

Increases down the group

Due to larger atomic size and stronger van der Waals forces of attraction.

Question 2

What is the trend in electronegativity down group 7?

Answer 2

Decreases

More occupied electron shells lead to a greater atomic radius and lower force of attraction.

Question 3

What do you use to test for halide ions?

Answer 3

Acidified AgNO3

Question 4

Why do you add HNO3 instead of HCl when testing for halide ions?

Answer 4

To remove CO₃²⁻; adding HCl would introduce Cl⁻ ions, causing a false positive.

Question 5

What is the result and equation for the test for Cl⁻?

Answer 5

White ppt
Ag⁺ + Cl⁻ → AgCl (s)

Question 6

What is the result and equation for the test for Br⁻?

Answer 6

Cream ppt
Ag⁺ + Br⁻ → AgBr (s)

Question 7

What is the result and equation for the test for I⁻?

Answer 7

Yellow ppt
Ag⁺ + I⁻ → AgI (s)

Question 8

What happens to AgCl when dilute or concentrated NH3 is added?

Answer 8

AgCl dissolves in both dilute and concentrated NH3
AgCl (s) + 2NH₃ (aq) → [Ag(NH₃)₂]⁺ (aq) + Cl⁻

Question 9

What happens to AgBr when concentrated NH3 is added?

Answer 9

AgBr dissolves only in concentrated NH3
AgBr (s) + 2NH₃ (aq) → [Ag(NH₃)₂]⁺ (aq) + Br⁻

Question 10

What happens to AgI when NH3 is added?

Answer 10

AgI will not dissolve in either dilute or concentrated NH3.

Question 11

What is the trend in oxidising ability down group 7?

Answer 11

Decreases down the group

Cl is the best oxidising agent, while I is the worst.

Question 12

Write the equation for Cl2 oxidising 2I⁻.

Answer 12

Cl₂ + 2I⁻ → 2Cl⁻ + I₂

Question 13

What is the trend in reducing ability of the halides down the group?

Answer 13

Increases down the group

I⁻ is the best reducing agent, while Cl⁻ is the worst.

Question 14

What products are formed when I⁻ reduces H₂SO₄?

Answer 14

H₂SO₄ + 2I⁻ → SO₄²⁻ + 2HI
H₂SO₄ + 2H⁺ + 2I⁻ → SO₂ + I₂ + 2H₂O
H₂SO₄ + 6H⁺ + 6I⁻ → S + 3I₂ + 4H₂O
H₂SO₄ + 8H⁺ + 8I⁻ → H₂S + 4I₂ + 4H₂O

Question 15

What are the products of Br⁻ + H₂SO₄?

Answer 15

HBr and SO₂

Question 16

Does Cl⁻ reduce H₂SO₄?

Answer 16

No, not a powerful enough reducing agent; only HCl is formed.

Question 17

Why is chlorine added to drinking water?

Answer 17

Forms ClO⁻ ions which oxidise (kill) microorganisms in water.

Question 18

What are the potential risks of adding chlorine to drinking water?

Answer 18

Chlorine is toxic and can form carcinogens with hydrocarbons.

Question 19

Why is ozone not used to purify water in the UK?

Answer 19

More expensive than chlorine and evaporates from water quickly.

Question 20

What is the equation for the reaction of Cl₂ with water?

Answer 20

Cl₂ (g) + H₂O (l) → HClO (aq) + HCl (aq)

Question 21

What type of reaction is the reaction of chlorine with water?

Answer 21

Disproportionation

Question 22

What are the two forms of the chlorate ion?

Answer 22

ClO⁻ is chlorate (I)
ClO₃⁻ is chlorate (V)

Question 23

What is the equation for making bleach?

Answer 23

Cl₂ + 2NaOH → NaCl + NaClO + H₂O

Question 24

Give the equation for the reaction of chlorine and water in the presence of sunlight.

Answer 24

2Cl₂ + 2H₂O → 4HCl + O₂ (g)

Question 25

What is desalination?

Answer 25

Converts saltwater into clean, potable water

Either by reverse osmosis or vacuum distillation.

Question 26

What are the advantages and disadvantages of desalination?

Answer 26

Advantages:
* Safe, clean, drinkable water produced
Disadvantages:
* Uses a lot of energy
* Low efficiency
* Can disturb marine ecosystems