3.2.3 Group 7(17), the halogens

Question 1

Electronegativity trend for halogens

Answer 1

Decreases down the group because shielding and atomic radius decreases, meaning the outer electrons are further from the nucleus. So they are less strongly attracted to the nucleus, so lower electronegativity

Question 2

Boiling point trend of halogens

Answer 2

Increases down the group as atomic radius increases, meaning the diatomic molecules are larger so have stronger VDWs

Question 3

Oxidising ability trend of HALOGENS

Answer 3

Halogens become less oxidising as you move down the group as it is more difficult to gain an electron. Displacement reactions are a good test of this

Question 4

Reducing ability trend of HALIDES

Answer 4

Increases down the group as atomic radius increases, so outer electrons held with less attraction, so more easily lost

Question 5

Which halogens can displace halide ions

Answer 5

More reactive halogens can displace less reactive halogens
F2 can displace all halides
Cl2 can displace all halides except F-
etc
I2 cannot displace any (except At-)

Question 6

Reactivity trend of halogens

Answer 6

Decreases down the group as greater atomic radius and shielding means it is harder to accept an electron

Question 7

Sodium chloride + CONCENTRATED sulfuric acid

Answer 7

NaCl + H2SO4 –> NaHSO4 + HCl
OR
2NaCl + H2SO4 –> Na2SO4 + 2HCl

Question 8

Sodium bromide + CONCENTRATED sulfuric acid

Answer 8

2NaBr + 2H2SO4 –> Na2SO4 + Br2 + SO2 + 2H2O

Question 9

Sodium iodide + CONCENTRATED sulfuric acid

Answer 9

8NaI + 5H2SO4 –> 4Na2SO4 + 4I2 + H2S + 4H2O

Question 10

Test for halide ions

Answer 10

1. Add dilute nitric acid
2. Add silver nitrate
3. white ppt (Cl-), cream ppt (Br-), yellow ppt (I-)

Question 11

Why is dilute nitric acid added to test for halides

Answer 11

Remove any ions (hydroxide/carbonate) that could give ppts with AgNO3

Question 12

Why is silver nitrate used to identify halide ions

Answer 12

AgNO3 forms ppts with halides

Question 13

Suggest why an excess of AgNO3 is used

Answer 13

To ensure all halide ions are removed from the solution

Question 14

Why is dilute and concentrated ammonia added after the AgNO3 halide test

Answer 14

AgCl dissolves in both
AgBr dissolves in concentrated ammonia solution
AgI does not dissolve in neither

Question 15

Solubility in ammonia trend in halogens

Answer 15

Decreases down the group as atomic radius increases making it hared to gain an electron

Question 16

Chlorine with water reactions

Answer 16

Cl2 + H2O –> HCl + HClO
In sunlight - 2Cl2 + 2H2O –> 4HCl + O2

Question 17

Why is chlorine used to treat water

Answer 17

The benefits to health of water treatment by chlorine outweigh its toxic effects.

Question 18

What does chlorine do in water

Answer 18

Kill bacteria

Question 19

The reaction of chlorine with cold, dilute, aqueous NaOH and uses of product

Answer 19

Cl2 + 2NaOH –> NaCl + NaClO + H2O
NaClO is used in production of bleach

Question 20

Test for NH4+ ions

Answer 20

Add dilute sodium hydroxide and warm
If NH4+ ions present, ammonia released which turns red litmus paper blue

Question 21

Test for carbonate ions

Answer 21

Add dilute acid
If carbonate ion present a gas will be produced which if bubbled through limewater will turn the limewater cloudy

Question 22

Test for hydroxide ions

Answer 22

Turns damp red litmus paper blue

Question 23

Test for sulfate ions

Answer 23

Add BaCl2, white ppt formed

Question 24

Test for group 2 metal ions

Answer 24

Add BaCl2 this will displace the metal ions
Add NaOH to form group 2 hydroxides, then observe ppt formed
Add Sulfuric acid to form group 2 sulfates, then observe the ppt formed

Mg2+ - white ppt, no ppt
Ca2+ - white ppt, slight white ppt
Sr2+ - slight white ppt, white ppt
Ba2+ - no ppt, white ppt

OR FLAME TEST