2.3 Group 7 Elements

Question 1

What is the trend in boiling points of halogens?

Answer 1

Increase as you move down group 7, as as you increase the size of the atom there are more electrons to form Wan der Waal’s forces with each other, raising the energy required to break these molecules apart.

Question 2

What is the trend in electronegativity in halogens?

Answer 2

Decrease as you move down the group, as as the atoms get bigger the bonding pair is further away from the nucleus (so there is less attraction) and there is more shielding.

Question 3

What is the trend in oxidising power of halogens?

Answer 3

Cl2 > Br2 > I2

As it is harder to gain an electron as the atoms become larger and there is more shielding

Question 4

What is the trend in reducing power of the halogens?

Answer 4

The further down group 7 the greater the reducing power, as the larger atoms have more shielding and can therefore lose more atoms.

Question 5

Describe the reduction of sulfuric acid with fluoride ions?

Answer 5

Very weak reducing agent so there is no redox reaction, only an acid-base reaction, eg
NaF + H2SO4 -> NaHSO4 + HF

Question 6

Describe the reduction of sulfuric acid with chloride ions?

Answer 6

Very weak reducing agent so there is no redox reaction, only an acid-base reaction, eg
NaCl + H2SO4 -> NaHSO4 + HCl
HCl Forms steamy fumes

Question 7

Describe the reduction of sulfuric acid with bromide ions ?

Answer 7

First there is an acid-base reaction 
NaBr + H2SO4 -> NaHSO4 + HBr
The Br- is a strong reducing agent 
2HBr +H2SO4 -> Br2 + SO2 + 2H20
-HBr Forms steamy fumes
-Br2 forms brown gas 
-SO2 forms colourless gas

Question 8

Describe the reduction of sulfuric acid with iodide ions?

Answer 8

First there is an acid-base reaction 
NaI + H2SO4 -> NaHSO4 + HI
The I- is a strong reducing agent 
8HI + H2SO4 -> 4I2 + H2S + 4H2O
-S Forms a yellow solid (occurs if 6HI)
-HI forms steamy fumes 
-I2 forms purple fumed 
-H2Sforms a bad egg smell

Question 9

What is the reaction of chlorine and water?

Answer 9

Cl2 + H20 -> HCl + HClO (chloric acid)
One chlorine atom is reduced to form Cl-
One chlorine atom is oxidised to form Cl+

Question 10

What is the use of the Chlorate (ClO-) ion

Answer 10

It is a powerful disinfectant and bleach

Question 11

What is the reaction between chlorine and sodium hydroxide?

Answer 11

Cl2 + 2NaOH -> NaCl + NaClO (sodium chlorate) + H2O

Question 12

What is the use of the sodium chlorate ion?

Answer 12

It is a key ingredient in chlorine based bleach

Question 13

What happens when you warm sodium chlorate above 75°C

Answer 13

Disproportionate, forming chloride ions and chlorate ions

3ClO- -> 2Cl- + Cl(O3)-

Question 14

What is the use of the sodium chloride (v) ion?

Answer 14

Used as a weed killer

Question 15

What does the silver nitrate solution test for?

Answer 15

The presence of halide ions

Question 16

Describe the silver nitrate test

Answer 16

1) add NaOH to the solution and warm
2) acidity using HNO3
3) Add silver nitrate solution
4) check which precipitate is formed using the ammonia test.

Question 17

What observation should you see if Cl- ions are present during the silver nitrate test ?

Answer 17

A white precipitate

Question 18

What observation should you see if Br- ions are present during the silver nitrate test ?

Answer 18

A cream precipitate

Question 19

What observation should you see if I- ions are present during the silver nitrate test ?

Answer 19

A pale yellow precipitate

Question 20

What observation should you see if AgCl is present if you add dilute ammonia, and concentrated ammonia?

Answer 20

Precipitate redissolves after the addition of dilute ammonia

Question 21

What observation should you see if AgBr is present if you add dilute ammonia, and concentrated ammonia?

Answer 21

Precipitate redissolves after addition of concentrated ammonia

Question 22

What observation should you see if AgI is present if you add dilute ammonia, and concentrated ammonia?

Answer 22

No change