Reactions of halide ions

Question 1

How do halide ions act as reducing agents?

Answer 1

the ions lose electrons to become halogen molecules

Question 2

What is the trend in their reducing ability? Why does this occur?

Answer 2

increases down the group linked to the size of the ions - the larger the ion, the more easily it loses an electron

this is because the electron is lost from the outer shell which is further from the nucleus as the ion gets larger

so the attraction to the outer electron is less

Question 3

How can the trend in reducing ability be seen?

Answer 3

reactions of solid sodium halides with concentrated sulfuric acid

Question 4

What is the equation for the reaction for sodium chloride sulfuric acid and what type of a reaction is it?

Answer 4

NaCl (s) + H2HSO4 (l) → NaHSO4 (s) + HCl (g)

not a redox reaction because no oxidation state has changed

the chloride ion is too weak as a reducing agent to reduce the sulfur (oxidation state = +6) in sulfurice acid, it is an acid-base reaction

Question 5

What are the observations when drops of conc sulfuric acid are added to sodium chloride

Answer 5

steamy fumes of hydrogen chloride are seen

the solid product is sodium hydrogensulfate

Question 6

What are the reactions that occur in sodium bromide with sulfuric acid? what are the changes in oxidation state

Answer 6

sodium hydrogensulfate and hydrogen bromide are produced- similar acid-base reaction to sodium chloride

NaBr (s) + H2SO4 (l) → NaHSO4 (s) + HBr (g)

then bromide ions convert sulfuric into sulfur dioxide

the oxidation state of the sulfur is reduced from +6 to +4 and that of the bromine increases from -1 to 0

2H⁺ + 2Br^{- -1} + H₂SO₄ ⁺⁶ (l) → SO2 ⁺⁴ (g) + 2H₂O (l) + Br₂ (l)

Question 7

What are the observations when drops of conc sulfuric acid are added to sodium bromide

Answer 7

steamy fumes of hydrogen bromidne and colourless sulfur dioxide is formed

reacts w/ sulfuric acid

exothermic

some bromine vaporises

Question 8

What sort of reaction is it (sodium bromide + sulfuric acid)? why does this occur? What are the changes in oxidation state

Answer 8

redox reaction

bromide ions are strong enough reducing agents to reduce the sulfuric acid to sulfur dioxide

• Br - -1 to 0
• S - +6 to +4

Question 9

What are the two reactions that occur when sodium bromide and conc sulfuric acid react?

Answer 9

• NaBr (s) + H₂SO₄ (l) → NaHSO₄ (s) + HBr (g)
  
  • similar acid-base reaction to sodium chloride
• 2H⁺ + Br^- + H₂SO₄ (l) → SO2 (g) + 2H₂O (l) + Br₂ (l)
  
  • strong enough reducing agents

Question 10

What reaction occur in sodium iodide with sulfuric acid? include oxd state of sulfur and iodine in the second equation

Answer 10

acid-base reaction:

NaI (s) + H₂SO₄ (l) → NaHSO₄ (s) + HI (g)

2nd:

8HI ^-1 + H₂S⁶⁺O₄ (l) → H₂S ^-2 (g) + 4H₂O (l) + 4I₂ (s)

Question 11

Why does iodine reduce the sulfur in sulfuric acid even further? What effect does this have on the reaction?

What are the changes in oxd state

Answer 11

iodine ions are better reducing agents then bromide ions so they reduce the sulfur in sulfuric acid even further

• I - -1 to zero
• S - +6 to -2

Question 12

WHat are the observation when sulfuric acid and sodium iodide react

Answer 12

steamy fummes of hydrogen iodide, the black solid iodide, the bad egg smell of hydrogen sulfide

yellow solid sulfur may be seen

colourless sulfur dioxide evolved

Question 13

What are the properties of a silver halide? How is it produced?

Answer 13

all metal halides (except fluoride) react with silver ions in aqueous solution

e. g. silver nitrate reacts to form a percipitate of the insoluble silver halide
e. g. Cl^- + Ag⁺ → AgCl (s)

Question 14

Why does silver fluoride not form a precipitate?

Answer 14

it is soluble in water

Question 15

Identifying metal halides with silver ions - How are impurities removed? Why do they need to be removed? (probs dont need to learn all the equations)

Answer 15

• dilute nitric acid (HNO₃^-) or (H⁺ (aq) + NO₃^-(aq)) added to the halide solution to get rid of any soluble carbonate (CO₃^2-), or hydroxide impurities
  
  • CO₃^2- (aq) + 2HNO₃^-(aq) → CO² (g) + H₂O (l) + 2NO₃^- (aq)
  • OH^- (aq) + H⁺ (aq) + NO^3- (aq) → H₂O (l) + NO^3- (aq)
• These would interfere with the test in two ways:
  
  • forming insoluble silver carbonate -
    
    • 2Ag⁺ (aq) + CO₃^2- (aq) →Ag₂CO³ (s)
  • or insoluble silver hydroxide -
    
    • Ag⁺ (aq) + OH^- (aq) → AgOH (s)

Question 16

How are halides identified?

Answer 16

• add a few drops of silver nitrate solution and the halide precipitate will form

need to finish

Question 17

What are the different colours and further tests for the silver halides>

Answer 17

silver fluoride - no percipitate

silver chloride - white ppt - dissolves in dilute ammonia

silver bromide - cream ppt - dissolves in conc. ammonia

silver iodide - pale yellow ppt - insoluble in conc. ammonia

Question 18

What can also form a cream precipitate?

Answer 18

a mixture of silver chlorine and silver bromine

Question 19

Write the ovarall equation for the reaction of sodium bromide and sulfurice acid?

Answer 19

• 2NaBr + 2H₂SO₄ → Na₂SO₄ + Br₂ + SO₂ + H₂O

Question 20

Why do bromide ions react differently the chloride ions>?

Answer 20

• Br- bigger than Cl-
• Br- more easily oxidised

Question 21

How can a mixture of sodium chloride and bromide be separated?

Answer 21

Stage 1: formation of precipitates

• Add silver nitrate
• to form precipitates of AgCl and AgBr
• AgNO3 + NaCl → AgCl + NaNO3
• AgNO3 + NaBr → AgBr + NaNO3

Stage 2: selective dissolving of AgCl

• Add excess of dilute ammonia to the mixture of precipitates
• the silver chloride precipitate dissolves
• AgCl + 2NH3 → Ag(NH₃)₂ + + Cl⁻

Stage 3: separation and purification of AgBr

• Filter off the remaining silver bromide precipitate
• Wash to remove soluble compounds
• Dry to remove water