Group 7

Question 1

Use of Chlorine (Cl2)

Answer 1

Treatment of water to make it clean and drinkable
It is toxic but the positive effects outweigh this
Cl2 + H20 —> HCL + HClO

Question 2

Another use of Chlorine (Cl2)

Answer 2

Produce a compound used in the manufacture of bleach
Cl2 + 2NaOH —> NaCl + NaClO

Question 3

What do you use to test for halide ions

Answer 3

Acidified AgNO3

Question 4

Why do you add HNO3? Why not HCL?

Answer 4

To remove CO3 (2- ion)
Adding HCL would add Cl- ions, giving a false white precipitate

Question 5

What are the results for the test of F-, Cl-, Br- and I-

Answer 5

F- = colourless
Cl- = white
Br- = cream
I- = yellow

Question 6

What happens to each silver halide when dilute/conc NH3 is added?

Answer 6

AgCl = redissolves the precipitate in dilute NH3
AgBr = precipitate remains in dilute, redissolves in conc
AgI = precipitate remains in both dilute and conc

Question 7

Trend in electronegativity down Group 7

Answer 7

Decreases
Greater atomic radius and outer electron further from the nucleus (weaker attraction)
Increased shielding

Question 8

Trend in boiling point down group 7

Answer 8

Increases
Size of the atom increases
Increases strength of Van Der Walls
More energy required to overcome them

Question 9

Which element has the best oxidising ability and worst?

Answer 9

Best = Cl
Worst = I

Question 10

What products are formed when I- reduces H2SO4? Do all 4 equations

Answer 10

NaI + H2SO4 —> NaHSO4 + HI
2HI + H2SO4 —> I2 + 2H2O + SO2
6HI + SO2 —> H2S + 3I2 + 2H2O
Combine the last two :
8HI + SO2 —> 4H2O + 4I2 + H2S
Strongest reducing agent

Question 11

Cl- reducing H2SO4

Answer 11

It does not reduce (redox), only a displacement reaction
NaCl + H2SO4 —> HCL + NaHSO4

Question 12

Br- reducing H2SO4 equations

Answer 12

NaBr + H2SO4 —> HBr + NaHSO4
2HBr + H2SO4 —> Br2 + 2H2O + SO2