group 7 halogens

Question 1

What is the trend for group 7 halogens?

Answer 1

• Electronegativity decreases down the group
• Boiling points increases down the group as more electrons = more london forces
• 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, so more energy is required to gain an electron and become reduced
- More reactive halogens displace less reactive halide ions in solution

Question 4

Results of chloride in a silver precipitate

Answer 4

White colour
Soluble - dilute ammonia
Soluble - concentrated ammonia

Question 5

Results of bromine in a silver precipitate

Answer 5

Cream colour
Insoluble - dilute ammonia
Soluble - concentrated ammonia

Question 6

Results of iodine in a silver precipitate

Answer 6

Yellow colour
Insoluble - dilute ammonia
Insoluble - concentrated ammonia

Question 7

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

Answer 7

Cl2 + H20 -> HCL + HOCl, disproportionation
- 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 8

What is the use of chlorine as a bleach

Answer 8

Cl2 + 2NaOH -> NaOCl + H2O + NaCl, disproportionation
- cold, dilute sodium hydroxide forms sodium chlorate (I)
- hot sodium hydroxide forms sodium chlorate(V)