The Halogens

Question 1

What do all the halogen exist as?

Answer 1

Diatomic molecules

Question 2

What physical trend occurs down the halogen group?

Answer 2

Melting/ Boiling points increase

Question 3

Why do the halogens melting/ boiling points increase down the group?

Answer 3

As the group descends more electrons are present in the elements atom, leading to stronger induced dipole-dipole (london) forces between the molecules, therefore requiring more energy to overcome the stronger intermolecular forces.

Question 4

What test is used to see the difference of halogen reactivities?

Answer 4

Halogen-halide displacement

Question 5

Describe halogen halide displacement

Answer 5

A solution of halogen is added to an aqueous halide solution (of another halogen), the the halogen added is more reactive a colour change will occur as the halide is displace by the halogen. The displaced halide froms a new colour solution, which can be seen.

Question 6

Write the colours of Cl2 Br2 and I2 in water

Answer 6

Cl2 = Pale green
Br2 = Orange
I2 = Brown

Question 7

Write the colours of Cl2 Br2 and I2 in Cyclohexane

Answer 7

Cl2 = Pale green
Br2 = Orange
I2 = Violet

Question 8

Why do halogens become less reactive?

Answer 8

Halogens gain electrons, however as the groups descends the nuclear attraction of the halogens decreases. becauses their atomic radius increases aswell as electron sheilding, outweighing the increase in nuclear charge.
This therefore creates a decrease in reactivity.

Question 9

What is a disproportionation reaction?

Answer 9

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

Question 10

Name the two studied disproportionation reactions

Answer 10

1. Chlorine and water.
2. Chlorine and cold dilute aqueous sodium hydroxide

Question 11

What is the equation for the reaction between chlorine and water?

Answer 11

Cl2 (aq) + H2O (l) -> HClO (aq) + HCl (aq)

Question 11

Why is cold dilute aqueous sodium hydroxide reacted with chlorine instead of water?

Answer 11

Chlorine has a low solubility in water, cold dilute aqueous sodium hydroxide helps increase the solubility, althoug it starts amnother disproportionation reaction.

Question 12

How is the bateria killed when chlorine is added to water?

Answer 12

Chloric acid and chlorate ions (ClO-)

Question 13

Write the equation for the reaction between Chlorine and cold dilute aqueous sodium hydroxide

Answer 13

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

The chlorine in NaClO is oxidised
The Chlorine in NaCl is reduced

Question 14

What is the benefit of adding Chlorine to drinking water?

Answer 14

Kills bacteria

Question 15

What are the risks of adding Chlorine to drinking water?

Answer 15

1. Chlorine is a toxic gas which can irritate the lung in low concs and kill in high concs
2. Chlorine reacts with organic hydrocarbons to form Chlorinated hydrocarbons, suspected to cause cancer.

Question 16

What must be taken into consideration before adding chlorine to water?

Answer 16

the circumstances, Chlorine should not be adde to water if there is no danger (bacteria present).