group 7 [I1] PAPER 1

Question 1

trend in electronegativity down group 7 and why?

Answer 1

• decreases down group
• more shells, so more shielding
• weaker attraction between the nucleus and pair of electrons in the covalent bond

Question 2

trend in atomic radius down group 7 and why?

Answer 2

• increases down group
• more shells
• bigger atom

Question 3

trend in melting and boiling points down group 7 and why?

Answer 3

• increases
• more electrons
• molecule gets bigger
• more van der Waals’ forces between the molecules
• more energy required to overcome these forces

Question 4

trend in first ionisation energy down group 7 and why?

Answer 4

• decreases down group
• more shells, so more shielding
• weaker attraction between nucleus and outer electron

Question 5

trend in oxidising power down group 7 and why?

Answer 5

• decreases down group
• atomic radius increases, so gets larger
• more shielding
• weaker forces of attraction between nucleus and electron to be gained

Question 6

what does the relative oxidising strengths of the halogens give them the ability to do?

Answer 6

• displace one another
• Cl2 will displace both Br- and I- ions
• Br2 will displace I- ions
• I2 won’t displace any halide ions
• what happens to each thing can be written as half equations

Question 7

what is oxidising power?

Answer 7

ability to gain an electron

Question 8

trend in reducing ability of halide ions and why?

Answer 8

• increases down group
• more shielding
• atomic radius increases
• weaker attraction between outer electron that is lost and the nucleus

Question 9

equation, reaction type and observations for the reaction between solid NaF / NaCl and conc. sulfuric acid?

Answer 9

• NaF + H2SO4 → NaHSO4 + HF
• NaCl + H2SO4 → NaHSO4 + HCl
• steamy fumes
•reaction type - acid-base

Question 10

equations, reaction types and observations for the reaction between solid NaBr and conc. sulfuric acid?

Answer 10

Question 11

equations, reaction types and observations for the reaction between solid NaI and conc. sulfuric acid?

Answer 11

Question 12

ability of halide ions to reduce sulfuric acid?

Answer 12

Question 13

how to test for halide ions?

Answer 13

• add silver nitrate solution that has been acidified by dilute nitric acid (acidified to remove ions that may interfere with results, so result in false positive results)
• chloride ions produce a white precipitate (AgCl)
• bromine ions produce a cream precipitate (AgBr)
• iodide ions produce a yellow precipitate (AgI)

to distinguish between the precipitates:
• AgCl dissolves in dilute ammonia
• AgBr dissolves in conc. ammonia
• AgI doesn’t dissolve any ammonia solution

Question 14

equation for the reaction of chlorine with water?

Answer 14

Cl2 + H2O ⇌ HCl + HClO

Question 15

equation for the reaction of chlorine with water, in the presence of UV light?

Answer 15

2Cl2 + 2H2O ⇌ 4HCl + O2

Question 16

equation for the reaction between cold, aqueous NaOH and chlorine, and use of the product formed?

Answer 16

sodium chlorate (I) solution is an ingredient of bleach and used to disinfect

Question 17

Chlorine is used to treat water, despite being toxic to humans. Why is water treated with chlorine, and why is it used, despite the toxicity?

Answer 17

• sterilises water
• health benefit outweighs the risk and it is only used in small quantities/low concentrations

Question 18

What is observed when silver nitrate solution is added to sodium fluoride solution?

Answer 18

Colourless solution

Question 19

What is the role of (1) halide ions and (2) sulfuric acid when reacting with conc. sulfuric acid to form NaH2SO4 and HX [X = halogen]?

Answer 19

(1) base / proton acceptor
(2) proton donor

Question 20

Halide ions reactions and observations (no organic solvent)

Answer 20

Question 21

Halide ions reactions and observations (with organic solvent)

Answer 21

Question 22

Explain why some of the reactions that occur when sodium bromide/iodide react with conc. sulfuric acid are redox reactions.

Answer 22

• Br/I changes oxidation state from -1 to 0 and is oxidised
• S changes oxidation state from +6 to +4/0/-2 and is reduced

Question 23

Explain why bromide ions react differently from chloride ions

Answer 23

• Bromide ions are bigger than chloride ions
• So, bromide ions are more easily oxidised

Question 24

A colourless solution contains a mixture of sodium bromide and sodium chloride.

Using aqueous silver nitrate and any other reagents of your choice, develop a procedure to prepare a pure sample of silver bromide from this mixture.

Explain each step in the procedure and illustrate explanations with equations, where appropriate.

Answer 24

• Add silver nitrate to form precipitates of AgCl and AgBr:
– AgNO3 + NaCl → AgCl + NaNO3
– AgNO3 + NaBr → AgBr + NaNO3
• Add an excess of dilute ammonia to the mixture of precipitates to dissolve the AgCl precipitate:
– AgCl + 2NH3 → Ag(NH3)2+ + Cl-
• Filter off the remaining silver bromide precipitate
• Wash to remove soluble compounds
• Dry to remove water

Question 25

A solution of sodium chlorate(l) was added to a colourless solution of potassium iodide.

Suggest what is observed.

Explain the reaction that leads to this observation.

Answer 25

Goes brown due to iodine, because iodide ions are oxidised.

Question 26

State which gas produced in the reaction between solid NaI and conc. H2SO4 smells gross

Answer 26

hydrogen sulfide (H2S)

Question 27

Equation for the addition of ammonia to AgX precipitate when testing for halide ions with silver nitrate solution and ammonia?

[X = halogen]

Answer 27

AgX + 2NH3 → Ag(NH3)2+ + X-

Question 28

Suggest a disadvantage of treating water with chlorine.

Answer 28

• Wasteful as most potable water isn’t used for drinking
• Some people suffer eye irritation
• Some people find the taste unpleasant
• Can react with organic compounds to produce harmful substances

Question 29

Answer 29