Group 7 Elements

Question 0

The oxidising power of a halogen is a measure of…

Answer 0

The strength with which a halogen is able to attract and capture and electron to form a halide ion

Question 1

Describe and explain the trend in boiling points of Cl2, Br2 and I2

Answer 1

It takes more energy to break the van der Waals’ forces as you go down the group. This is because the number of electrons increasing, increasing the strength of the van der Waals’

Question 2

Describe and explain the reactivity of group 7 elements

Answer 2

Reactivity decreases down the group because the elements gain an extra electron shell. This increases the atomic radius and the amount of electron shielding within the atom. This decreases the attraction between the electrons and the nucleus, and so the ability to attract and capture and electron decreases

Question 3

Cl2 (aq) + 2Br- (aq) –>

Answer 3

2Cl- (aq) + Br2

Chlorine ions displace the bromine ions because chlorine is more reactive and more easily forms 1- ions

Question 4

Cl2 (aq) + 2I- (aq) –>

Answer 4

2Cl- (aq) + I2 (aq)

Chlorine ions displace iodine ions because chlorine is more reactive and more easily forms 1- ions

Question 5

Br2 (aq) + 2I- (aq) –>

Answer 5

2Br- (aq) + I2 (aq)

Bromine ions displace iodine ions because bromine is more reactive and more easily forms 1- ions

Question 6

Colour of Cl2 in water and cyclohexane

Answer 6

Pale green in water, darker green in cyclohexane

Question 7

Colour of Br2 in water and cyclohexane

Answer 7

Orange in water, darker orange in cyclohexane

Question 8

Colour of I2 in water and cyclohexane

Answer 8

Yellow in water, purple in cyclohexane

Question 9

Chlorine as used in water purification

Answer 9

Cl2 (aq) + H2O (l) –> HClO (aq) + HCl (aq)
Small amount of chlorine are added to drinking water to kill bacteria
However, chlorine gas is toxic

Question 10

Chlorine as used in bleach production

Answer 10

Cl2 (aq) + 2NaOH (aq) –> NaCl (aq) + NaClO (aq) + H2O (l)

The NaOH must be cold and dilute

Question 11

What is a disproportionation reaction?

Answer 11

A reaction in which the same element is both oxidised and reduced

Question 12

What is NaCl used for?

Answer 12

It is common salt

Question 13

What is NaF used for?

Answer 13

It is added to toothpaste, to eko prevent tooth decay

Question 14

What are crystals of CaF2 used for?

Answer 14

They are used to make lenses to focus infrared light

Question 15

How to test for halide ions

Answer 15

The unknown halide solution is dissolved in water
An aqueous solution of AgNO3 is added
Silver ions from the AgNO3 react with any halide ions present, forming a silver halide precipitate
The precipitate is coloured, which tells us which halide is present
If still unsure about the colour, add aqueous ammonia

Question 16

Chloride test results: testing for halides

Answer 16

Ag+ (aq) + Cl- (aq) –> AgCl (s)
White precipitate is formed
Silver chloride is soluble in dilute NH3 (aq)

Question 17

Bromide test results: testing for halides

Answer 17

Ag+ (aq) + Br- (aq) –> AgBr (s)
A cream precipitate will be formed
Silver bromide is soluble in concentrated NH3 (aq)

Question 18

What is the formula of bleach and what is the ion responsible for the bleaching?

Answer 18

NaClO

ClO-