Group 7 the Halogens ( AS )

Question 1

What is the trend in boiling point down group 7? Why?

Answer 1

Increases down the group
Because the size of the atom increases as there are more occupied electron shells—> stronger van der waals forces between molecules, takes more energy to break

Question 2

What is the trend in electronegativities down group 7? Why?

Answer 2

Decreases
Because there are more occupied electron shells—> greater atomic radius and outer electrons are further away from the positive charge of nucleus—> weaker force of attraction between nucleus and shared pair of electrons

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 CI3(2-)
Adding HCl would add Cl- ions, giving a false positive result

Question 5

Result and equation for Cl- test?

Answer 5

White precipitate
Ag+ + Cl- —> AgCl(s)

Question 6

What is the result and equation for the test for I-?

Answer 6

Yellow precipitate
Ag+ + I- —> Agl(s)

Question 7

What is the trend in oxidising ability down the group?

Answer 7

Decreases down the group(Cl best, I worse)
Because: Cl has fewest occupied electron shells, the greatest force of attraction between outer electrons and nucleus, easiest to gain electrons and be reduced—> best oxidising agent

Question 8

What is the trend in reducing the ability of the halides down the group? Why?

Answer 8

Increases down the group( Cl- worst, I- best)
Because: I- has the most occupied electron shells,so outer electrons are further away from the nucleus, weakest force of attraction between outer electrons and positive charge of nucleus —> easiest to be oxidised and lose electrons —> best reducing agent

Question 9

what products are formed when Iodide ions reduce H2SO4 ?

Answer 9

1) H2SO4 + 2I- —> 2HI + SO4 2-
2) H2SO4 + 2I- + 2H+ —> SO2 + I2 + 2H2O
3) H2SO4 + 6I- + 6H+ —> S + 3I2 + 4H2O
4) H2SO4 + 8H+ +8H- —> H2S + 4I2 + 4H2O

Question 10

what are the products of bromide ions + H2SO4?

Answer 10

Hbr and SO2

Question 11

do chloride ions reduce H2SO4?

Answer 11

No, not a powerful reducing agent only HCl is formed

Question 12

Why is chlorine added to drinking water? Why is it safe?

Answer 12

Forms ClO- ions which oxides( kills) all microorganisms in water

Question 13

What are the potential risks of adding chlorine to drinking water?

Answer 13

Chlorine is toxic and damages the respiratory system. In large quantities can form carcinogens with hydrocarbons

Question 14

Why is ozone not used to purify water?

Answer 14

More expensive than chlorine, evaporates from water quickly

Question 15

What is the equation for the reaction of Cl2 with water?

Answer 15

Cl2(g) + H2O(l) —> HClO(aq) + HCl(aq)

Question 16

What type of reaction is the reaction of chlorine with water?

Answer 16

Disproportionation; chlorine is both oxidised and reduced

Question 17

What are the two forms of the chlorate ions?

Answer 17

ClO- is chlorate(l)
ClO3 - is chlorate(V)

Question 18

What is the equation for making bleach?

Answer 18

Cl2 + 2NaOH—> NaCl + NaClO + H2O
NaClO is bleach

Question 19

Give the equation for the reaction of chlorine and water in the presence of sunlight?

Answer 19

2Cl2 + 2H2O —> 4HCl + O2(g)

Question 20

What is desalination?

Answer 20

Converts saltwater into clean,potable water either by reverse osmosis or by using vacuum distillation at low pressure and low temperature

Question 21

What are the advantages and disadvantages of desalination?

Answer 21

Advantages- safe,clean, drinkable water produced in places where it might not otherwise be available
Disadvantages- uses lots of energy, reverse osmosis has low efficency, can disturb marine ecosystems