group 7

Question 1

trend in electronegativity

Answer 1

• decreases down group
• atomic radius increases
• shielding increases

Question 2

trend in boiling points

Answer 2

• increases down group
• molecules increase in size
• stronger van de waals forces between molecules

Question 4

trend in oxidising ability

Answer 4

• decreases down group
• atoms get larger
• less attractions between nucleus and outer electrons
• harder to gain electrons (oxidise other species)

Question 5

displacement reactions

Answer 5

a more reactive halogen will displace a less reactive halide in a compound

Question 6

trend in reducing ability

Answer 6

• increases down group
• atoms get larger
• less attraction between nucleus and outer electrons
• easier for them to donate electrons (reduce another species)

Question 7

acid-base reactions between concentrated sulphuric acid and solid sodium halides

Answer 7

NaX (s) + H2SO4 (l) -> NaHSO4 (s) + HX (g)

Question 8

redox reaction of solid NaBr and concentrated H2SO4

Answer 8

2H+ + 2Br- + H2SO4 (l) -> SO2 (g) + 2H2O (l) + Br2 (l)

Question 9

redox reaction of solid NaI and concentrated H2SO4

Answer 9

2H+ + 2I- + H2SO4 (l) -> SO2 (g) + 2H2O (l) + I2 (l)
8H+ + 8I- + H2SO4 (l) -> H2S (g) + 4H2O (l) + 4I2 (s)

Question 10

test for halide ions

Answer 10

add acidified silver nitrate
F- = no visible change
Cl- = white precipitate
Br- = cream precipitate
I- = yellow precipitate

Question 11

simplest ionic equations in the test for halide ions

Answer 11

Ag+ + Cl- —> AgCl
Ag+ + Br- —> AgBr
Ag+ + I- —> AgI

Question 12

secondary test for halide ions

Answer 12

add ammonia solution to the silver halide precipitates
AgCl = dissolves in dilute & concentrated ammonia
AgBr = dissolves in concentrated ammonia only
AgI = doesn’t dissolve in dilute or conc NH3 (may lighten in colour)

Question 13

why is the test for halide ions acidified

Answer 13

to remove any soluble carbonate impurities which may cause a precipitate

Question 14

what acid is used to acidify silver nitrate

Answer 14

dilute nitric acid HNO3

Question 15

the reaction of chlorine with water

Answer 15

disproportionation (Cl is simultaneously oxidised and reduced)

Cl2 (g) + H2O (l) —> HClO (aq) + HCl (aq)

Question 16

reaction of chlorine and water in UV sunlight

Answer 16

2Cl2 (g) + 2H2O (l) - > 4HCl (aq) + O2 (g)

Question 17

reaction of chlorine and sodium hydroxide

Answer 17

Cl2 (g) + 2NaOH (aq) —> NaClO (aq) + NaCl (aq) + H2O (l)

NaClO used to make bleach