Group 7 (The Halogens)

Question 1

describe and explain the trends in oxidising ability of the halogens

Answer 1

as you go down group 7 the oxidising ability decreases

• more shielding = less attraction = less reactive
• therefore harder to be reduced and accept an electron

Question 2

what happens when chlorine reacts with bromide and iodide ions

Answer 2

bromide ions - displaces the bromide ions producing a yellow solution (bromine)

iodide ions - displaces the iodide ions producing a brown solution (iodine)

Question 2

describe and explain the trends in reducing ability of the halogen

Answer 2

as you go down group 7 the reducing ability increases

• more shielding = less attraction = easier to lose electron
• therefore easier to be oxidised and lose an electron

Question 3

describe and explain the trends in electronegativity of the halogens

Answer 3

as you go down the group the electronegativity deceases

• the number of principal energy levels increase
• weaker attraction between nucleus and electrons in the covalent bond

Question 3

describe and explain the trends in boiling point of the halogens

Answer 3

as you go down the group the boiling point increases

• the size of the atom increases
• therefore more VdW forces between the molecules that need to be broken

Question 4

how do iodide ions act as a reducing agent

Answer 4

-in acid base reactions they react with acids to form hydrogen halides and either sodium sulphate or sodium bisulphate

• in redox reactions they react with acids to form iodine(black/purple solid + gas), water and either sulfur dioxide (choking gas), hydrogen sulfide (smelly gas), or sulfur (yellow solid)

Question 5

what happens when bromine reacts with chloride and iodide ions

Answer 5

chloride ions - no reaction so no visible change

iodide ions - displaces the iodide ions producing a brown solution (iodine)

Question 5

what happens when iodine reacts with chloride and bromide ions

Answer 5

chloride ions - no reaction so no visible change

bromide ions - no reaction so no visible change

Question 6

how do bromide ions act as a reducing agent

Answer 6

-in acid base reactions they react with acids to form hydrogen halides and either sodium sulphate or sodium bisulphate

• in redox reactions they react with acids to form bromine(brown gas), sulfur dioxide (choking gas) and water

Question 6

how do fluoride and chloride ions act as a reducing agent

Answer 6

in acid base reactions they react with acids to form hydrogen halides and either sodium sulphate or sodium bisulphate

Question 7

how is chlorine used to make chlorine water

Answer 7

• reacts with water to form hydrochloric acid and chloric acid
• this mixture is called chlorine water
• when added to universal indicator it turns red as they’re both acids and then turns white as chloric acid is a very effective bleach

Question 7

what happens when chlorine is bubbled through water in bright sunlight

Answer 7

• hydrochloric acid and oxygen is produced
• the pale green colour from the chlorine disappears as the colourless oxygen gas is produced

Question 8

what happens when chlorine reacts with cold dilute sodium hydroxide

Answer 8

• they form sodium chlorate which is the active ingredient in household bleach

Question 8

how would you test for chloride ions and what would you observe

Answer 8

• react acidified silver nitrate with sodium chloride (aqueous solution)
• white precipitate will form (silver chloride is insoluble)

Question 9

how would you test for fluoride ions and what would you observe

Answer 9

• react acidified silver nitrate with sodium fluoride (aqueous solution)
• no visible change ( silver fluoride is soluble )

Question 9

how would you test for bromide ions and what would you observe

Answer 9

• react acidified silver nitrate with sodium bromide (aqueous solution)
• cream precipitate will form (silver bromide is insoluble)

Question 10

how would you test for iodide ions and what would you observe

Answer 10

• react acidified silver nitrate with sodium iodide (aqueous solution)
• yellow precipitate will form (silver iodide is insoluble)

Question 11

how would you fully distinguish between the silver halides when testing for halide ions

Answer 11

react them with ammonia

• silver chloride dissolves in dilute ammonia
• silver bromide only fully dissolves in concentrated ammonia
• silver iodide doesn’t dissolve in any conc of ammonia

Question 12

why must the silver nitrate be acidified before carrying out the reactions with the halogens

Answer 12

to remove OH⁻ and CO₃²⁻ ions which form precipitates with silver nitrate

Question 13

why cant you use hydrochloric acid to acidify the silver nitrate

Answer 13

• the chloride ions would interfere with the reactions and form a white ppt