Group 7

Question 1

Suggest, with reasons, the order of melting points for Br₂, SrCl₂ & ICl.

Answer 1

1) SrCl₂ - strong ionic bonds
2) ICl - dipole-dipole between molecules – weaker than ionic bonds but stronger than VDW
3) Br₂ - VDW forces between molecules – much weaker

Question 2

Write an equation for the reaction of chlorine with cold water.

Answer 2

Cl₂ + H₂O ⇌ HCl + HClO

Question 3

Suggest three disadvantages of treating water with chlorine.

Answer 3

• wasteful as most potable water is not used for drinking
• some people suffer eye irritation
• can react with organic compounds to produce harmful substances

Question 4

Explain why acid should be added before barium chloride when testing for sulphate ions.

Answer 4

• to remove any carbonate ions
• carbonate ions react with barium chloride to form barium carbonate
• which precipitates to give a false positive test for sulphate ions

Question 5

State why sulfuric acid should not be used to acidify barium chloride.

Answer 5

• sulfuric acid contains sulphate ion
• which reacts with barium chloride to form white precipitate

Question 6

Suggest why magnesium chloride wouldn’t be a suitable test for sulphate ions.

Answer 6

• reacts with sulphate ions to form magnesium sulphate
• magnesium sulphate is soluble
• will not form a precipitate to give any indication of a positive result

Question 7

Name the four halogens, their states and colour.

Answer 7

fluorine → yellow gas
chlorine → green gas
bromine → red/brown liquid
iodine → black solid

Question 8

State and explain the trend in electronegativity down group 7.

Answer 8

→ decreases down the group
→ shielding increases
→ nucleus is further away from shared pair of e-

Question 9

State and explain the trend in boiling points down group 7.

Answer 9

→ increases down the group
→ molecules get bigger & no. of electrons increases
→ stronger VDW forces hence requires more energy

Question 10

State the trend in oxidising ability down group 7.

Answer 10

decreases down the group.

Question 11

State the trend in reducing ability down group 7.

Answer 11

increases down the group

Question 12

Write the equation for the reaction between sodium chloride and sulphuric acid. State what this type of reaction is called.

Answer 12

NaCl + H₂SO4 → NaHSO4 + HCl
[acid base reaction]

Question 13

Write two equations for the reaction of sodium bromide with sulphuric acid. State what you would observe in each.

Answer 13

acid base reaction: (steamy fumes)
NaBr + H₂SO4 → NaHSO4 + HBr
redox reaction: (bromine vapour// brown)
2H+ + 2Br- + H₂SO4 → SO₂ (g) +2H₂O + Br₂

Question 14

Write an equation for the redox reaction between sodium iodide and sulphuric acid. State what each product is observed as.

Answer 14

8H+ + 8I- + H₂SO4 (l) → H₂S (g) + 4H₂O (l) + 4I₂ (s)
→ H₂S as smell of rotten eggs
→ iodine as black solid
→ sulphur as yellow solid (intermediate step)

Question 15

Describe how to test for halide ions.

Answer 15

1) dissolve in water to form aqueous solution
2) add acid to eliminate carbonate ions
2) add silver nitrate
3) silver halide is formed
4) AgF - no ppt, AgCl - white, AgBr - cream, AgI - yellow

Question 16

Explain why solutions need to be acidified when testing for halide ions.

Answer 16

1) solution may contain OH- / CO3- ions which can form AgOH/ Ag₂CO3
2) insoluble therefore form ppt to give false +ive
3) acid is added to remove these ions

Question 17

Describe a follow up test for halide ions using ammonium solution.

Answer 17

1) add dilute ammonia to each silver halide
2) silver chloride will dissolve to give colourless solution
3) add concentrated ammonia
4) silver bromide will dissolve
5) silver iodide is insoluble in all concentrations of ammonia

Question 18

State two disadvantages of chlorination.

Answer 18

→ toxic at high concentrations
→ wasteful (not all water is used for drinking)

Question 19

Write an equation for the reaction of chlorine with water under sunlight.

Answer 19

2Cl₂ (aq) + 2H₂O (l) → 4HCl (aq) + O₂ (aq)

Question 20

Write an equation for the reaction of chlorine with cold, dilute sodium hydroxide.

Answer 20

Cl₂ (aq)+ 2NaOH (aq) → NaClO (aq) + NaCl (aq)+ H₂O (l)

Question 21

State one use of NaClO

Answer 21

household bleach to kill bacteria & remove stains

Question 22

Give a reason why chlorine is not formed when solid potassium chloride reacts with concentrated sulphuric acid.

Answer 22

chlorine ions are weak reducing agents

Question 23

Explain why reducing ability increases down group 7.

Answer 23

→ electrons are easier to lose from larger ions due to shielding & larger atomic radius
→ therefore more easily oxidised