Group 7 elements

Question 1

Describe the trends in boiling points as you go down group 7.

Answer 1

They increase as the molecules get bigger and the van der Walls forces get stronger meaning more energy is needed to break them.

Question 2

Describe the trends in electronegativity as you go down group 7.

Answer 2

It decreases. This is because the atomic radius increases and the amount of shielding increases. This means that the attraction between the nucleus and the pair of electrons that make up the covalent bond decreases.

Question 3

What is the trend in oxidizing power as you down group 7?

Answer 3

It decreases

Question 4

Why does the oxidising power decrease as you go down group 7?

Answer 4

The atomic radius increases and the shielding increases. Even with the increase in nuclear charge the attraction between the nucleus and the outer shells decreases making it harder to gain an electron.

Question 5

Use equations to represent the oxidising power of chlorine, bromine and iodine.

Question 6

What is the trend in reducing power as you down group 7?

Answer 6

It increases.

Question 7

Use equations to represent the reducing power of chlorine, bromine, and iodine.

Question 8

What is the reaction of chlorine with water in the presence of UV light?

Question 9

How do you make bleach?

Answer 9

You react chlorine with sodium hydroxide to make NaClO and NaCl

Question 10

Why are chlorate ions used to treat water even if they are toxic?

Answer 10

They kill bacteria in the water which makes it safe to drink.

Question 11

What is the test for a halide ion?

Answer 11

You add silver nitrate and dilute nitric acid. If there is chlorine present a white precipitate will form. If there is bromine present a cream precipitate will form. If there is iodine present then a yellow precipitate will form.

Question 12

How can you tell apart the precipitates?

Answer 12

The chloride ions dissolve in dilute ammonia and the bromine ions dissolve in concentrated ammonia. The iodine ions react in neither.

Question 13

How do you test for group 2 ions?

Answer 13

1. The flame test. Dip a wire loop in concentrated HCl and then dip it into an unknown compound.
2. Add sodium hydroxide and a white precipitate should form except for barium.

Question 14

What colour do calcium ions burn with?

Answer 14

brick red

Question 15

What colour do strontium ions burn with?

Answer 15

red

Question 16

What colour do barium ions burn with?

Answer 16

pale green

Question 17

How do you test for ammonium ions?

Answer 17

A damp piece of red litmus paper will turn blue in the presence of ammonia.

Question 18

What is the test for sulfate ions?

Answer 18

You add dilute HCl and barium chloride and a white precipitate should form.

Question 19

How do you test for hydroxide ions?

Answer 19

Indicator paper.

Question 20

How do you test for carbonate ions?

Answer 20

Add dilute HCl and you should see fizzing as carbon dioxide is produced.

Question 21

How do you test for carbon dioxide?

Answer 21

Bubble the gas through limewater and if it turns cloudy then CO2 is present.