8.2 - The halogens

Question 1

What is the boiling trend for group 7 halogens?

Answer 1

• Boiling points increases down the group as more electrons = more/stronger London forces = more energy needed
• Form - ions

Question 2

What is the appearance of group 7 halogens? RTP

Answer 2

fluorine = pale yellow gas
chlorine = pale green gas
bromine = red-brown liquids
iodine = shiny grey-black solid

Question 3

What is the trend in reactivity for group 7 halogens?

Answer 3

• Decreases down the group
• Shielding and atomic radius increases, decreasing nuclear attraction
• More energy is required to gain an electron and become reduced
• More reactive halogens displace less reactive halide ions in solution

Question 4

What is a disproportionation reaction?

Answer 4

A redox reaction in which the same element has been oxidised and reduced

Question 5

Write the reaction of chlorine and water and show the disproportionation reaction

Answer 5

:)
Cl2 + H20 -> HOCl + HCL

Question 6

Write the reaction of chlorine and cold, dilute aqueous sodium hydroxide and show the disproportionation reaction

Answer 6

:)
Cl2 + 2NaOH -> NaOCl + NaCl + H2O

Question 7

What is the general equation of aqueous halide ions and aqueous silver ions?

Answer 7

Ag+(aq) + X-(aq) -> AgX(s)

Question 8

What is the use of chlorine as a disinfectant, give strengths and limitations

Answer 8

• HClO is an oxidising agent that treats water by killing bacteria
• Cl2 gas is toxic, it can react with methane to form chlorinated hydrocarbons which are carcinogens

Question 9

What is the use of chlorine as a bleach

Answer 9

• cold, dilute sodium hydroxide forms sodium chlorate (I)
• hot sodium hydroxide forms sodium chlorate(V)