Group 7

Question 1

In Group 7, the first four elements are, in increasing Mr, Fluorine, Chlorine, Bromine, Iodine.
Describe, generally, the look of each element.
Describe the look of bromine in solution, and iodine in solution.

Answer 1

-Fluorine: pale yellow gas
-Chlorine: pale green gas
-Bromine: red liquid: dense brown fumes
-Iodine: shiny grey solid: sublimes to a purple gas

Bromine water - orange solution
Iodine water - brown solution

Question 2

In group 7, there are trends in certain properties. One of these trends is melting point and boiling point.

Describe and explain this trend.

Answer 2

• the halogens are simple molecular substances
• as you go down the group, the Mr of the diatomic molecules increases
• so stronger vdW forces between molecules, as the electron cloud is larger
• so more energy required to overcome IMFs

Question 3

This question is about electronegativities.
Explain why the electronegativity of the halogens decreases down the group.

Answer 3

• As you go down the group, the number of e- shells increases
• the bonding pair of e-s is further from the nucleus, and greater shielding
• so weaker force of attraction between bonding pair and nucleus

Question 4

Trends in oxidising ability of the halogens

Answer 4

F2 is best oxidising agent

Question 5

Trends in reducing ability of the halides

Answer 5

I- is the best reducing agent

Question 6

Explain why iodide ions are stronger reducing agents than chloride ions.

Answer 6

• iodide ions have greater number of e- shells
• outer e- is further from the nucleus, and greater shielding
• so weaker nuclear force of attraction between outer e- and nucleus
• outer e- is more easily lost/ donated

Question 7

General reactions of NaF, NaCl, NaBr, NaI with H2SO4. Then, tests and observations.

Answer 7

GENERAL REACTIONS AND THEN OBSERVATIONS

• NaF:
  R1 : acid base
  NaF(s) + H2SO4(l) -> NaHSO4(s) + HF(g)
• NaCl:
  R1: acid base
  NaCl(s) + H2SO4(l) -> NaHSO4(s) + HCl(g)
• NaBr:
  R1: acid base
  NaBr(s) + H2SO4(l) -> NaHSO4(s) + HBr(g)
  R2: reduction of sulfur in H2SO4 from +6 to +4 in SO2, oxidation of bromine
  NaBr(s) + H2SO4(l) -> NaHSO4(s) + SO2(g) + Br2(g) + H2O(l)
• NaI:
  R1 : acid base
  R2 : reduction of sulfur from +6 to +4
  NaI(s) + H2SO4(l) -> NaHSO4(s) + SO2(g) + I2(s) + H2O(l)
  R3: reduction of sulfur from +6 to 0
  NaI(s) + H2SO4(l) -> NaHSO4(s) + S(s) + I2(s) + H2O(l)
  R4: reduction of sulfur from +6 to -2
  NaI(s) + H2SO4(l) -> NaHSO4(s) + H2S(g) + I2(s) + H2O(l)

OBSERVATIONS
NaF:
GAS - bubbles and fizzing
ACIDIC GAS HF- misty white fumes, turns moist blue litmus paper red
HF - concentrated ammonia fumes turns into a dense white gas

NaCl:
GAS - bubbles and fizzing
ACIDIC GAS - misty white fumes, turns moist blue litmus paper red
HCl - concentrated ammonia fumes turns into a dense white gas

NaBr:
R1
GAS - bubbles and fizzing
ACIDIC GAS - misty white fumes, turns moist blue litmus paper red
HBr - concentrated ammonia fumes turns into dense white gas
R2
Br2 - orange fumes produced
SO2 - rotten egg smell, and turns acidified potassium dichromate paper from orange to green

NaI:
R1
GAS - bubbles and fizzing
ACIDIC GAS - misty white fumes, turns moist blue litmus paper red
HI - concentrated ammonia fumes turns into dense white gas
R2, I2(s) and SO2
I2(s) - black solid and purple fumes
SO2 - turns acidified potassium dichromate paper from orange to green
R3, S(s)
S(s) - yellow solid formed
R4, H2S
H2S - turns acidified lead acetate paper from colourless to black