group 7 key equations

Question 1

properties of group 7 halogens at room temp - fluorine, chlorine, bromine and iodine

Answer 1

-fluorine: pale yellow gas, reactive
-chlorine: green, reactive gas, toxic (pale green/ colourless solution)
-bromine: red liquid, brown toxic fumes (yellow solution)
-iodine: grey black solid, purple gas (brown solution)

Question 2

displacement reactions of chlorine and iodine ions

Answer 2

Cl2 (aq) + 2I- (aq) —> 2Cl- (aq) + I2 (aq)

Question 3

testing for halide ions + positive test for precipitates forming

Answer 3

1. add nitric acid (HNO3) to get rid of unwanted ions - carbonate ions (CO2- 3), so doesnt interfere
2. add silver nitrate solution, to see a precipitate forms
   AgCl (s) white precipitate
   AgBr (s) cream precipitate
   AgI (s) yellow precipitate
3. add dilute ammonia then concentrated ammonia
   AgCl (s) dissolves in dilute and concentrated ammonia
   AgBr (s) dissolves in concentrated ammonia
   AgI does not dissolve and remain

Question 4

halids salts and sulfuric acid
- fluorine and chlorine acid base reactions observations
1. what are halides and the weakest?

Answer 4

-halides are reducing agents so becomes oxidised
-weakest reducing agents are fluoride and chloride - not redox as not strong enough reducing agents

acid base reactions
NaF (s) + H2SO4 (l) —> NaHSO4 (s) + HF (g)

NaCl (s) + H2SO4 (l) —> NaHSO4 (s) + HCl (g)

observations: white misty fumes

Question 5

halids salts and sulfuric acid
- bromine
1. acid base reaction
2. redox reaction
3. overall reaction and observations

Answer 5

stronger reducing agent (bromide)
acid base reaction
NaBr (s) + H2SO4 (l) —> NaHSO4 (s) + HBr (g)

redox
2H+ + 2Br- + H2SO4 —> Br2 + SO2 + 2H2o (l)

overall equation
2NaBr (s) + 3H2SO4 (l) —-> 2NaHSO4 (s) + SO2 (g) + Br2 (g) + 2H2O (l)

observations: orange fumes (Br2)
SO2 is colourlesss

Question 6

halide salts and sulfuric acid - iodine
1. acid base reaction + observatiosn
2. 3 redox equations + observations
3. disproportionation definition

Answer 6

acid base
NaI (s) + H2SO4 (l) —> NaHSO4 (s) + HI (g)

observations: HI white misty fumes

redox
2H+ + 2I- + H2SO4 —> I2 (s/g) + SO2 (g) + 2H2O (l)
observations: black solid/ purple fumes (I2) and acidic gas (SO2)

6H+ + 6I- + H2SO4 (l) —> 3I2 (s/g) + S (s) + 4H2O (l)
observations: black solid/ purple fumes (I2) and yellow solid (S)

8H+ + 8I- + H2SO4 (l) —> 4I2 (s) + H2S (g) + 4H2O (l)
observations: gas with bad egg smell

disproportionation reaction: element oxidises and reduces in the same reaction

Question 7

chlorine with water

Answer 7

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

Question 8

chlorine with water and sunlight: chlorine and water (ionic equation)
-purpose of chlorine

Answer 8

2Cl2 (g) + 2H2O (l) —> 4H+ + 4Cl- + O2

-chlorine kills the bacteria it is toxic but benefits outweigh the risk

Question 9

making bleach: chlorine with sodium hydroxide + observations

Answer 9

Cl2 (aq) + 2NaOH (aq) —> NaCl (aq) + NaClO (aq) + H2o (l)
green to colourless