Chapter 8 - Reactivity Trends (Part 2)

Question 1

What is disproportionation?

Answer 1

The simultaneous oxidation and reduction of the same element.

Question 2

Chlorine + Water → Chloric (I) acid (HClO) + Hydrochloric acid (HCl)
This is an example of what type of reaction?

Answer 2

Chlorine + Water → Chloric (I) acid (HClO) + Hydrochloric acid (HCl)

This is a disproportionation reaction. Chlorine is simultaneously oxidised (from 0 to +1 in HClO) and reduced (from 0 to -1 in HCl).

Question 3

Chlorine + Sodium Hydroxide (cold, dilute) → Sodium chlorate (I) (NaClO) + Water
What is this reaction used for?
This is an example of what type of reaction?

Answer 3

Chlorine + Sodium Hydroxide (cold, dilute) → Sodium chlorate (I) (NaClO) + Water

Sodium chlorate (I) is used in household bleach.

This is a disproportionation reaction. Chlorine is simultaneously oxidised (from 0 to +1 in NaClO) and reduced (from 0 to -1 in NaCl).

Question 4

Chlorine + Water → Chloric (I) acid (HClO) + Hydrochloric acid (HCl)
What is this reaction often used for?

Answer 4

Chlorine + Water → Chloric (I) acid (HClO) + Hydrochloric acid (HCl)

This reaction is used in water treatment to kill potentially harmful bacteria. Care is needed as chlorine is toxic and can react with hydrocarbons to form chlorinated hydrocarbons, which are carcinogenic.

Question 5

How can one test for carbonate ions?

Answer 5

• Add dilute nitric acid to the sample
• If bubbles are observed, bubble gas through limewater
• If limewater turns cloudy, the gas is carbon dioxide and carbonate ions are present.

Question 6

How can one test for sulfate ions?

Answer 6

• Add aqueous barium chloride or barium nitrate to sample
• If white precipitate of barium sulfate is formed, sulfate ions are present.

Ba^2+ (aq) + SO4^2- (aq) → BaSO4 (s)

Question 7

How can one test for halide ions?

Answer 7

• Add aqueous silver nitrate (AgNO3) to the solution
• If a precipitate is formed, the solution contains halide ions.
• If it is difficult to identify the colour of the silver halide precipitate, its solubility in aqueous ammonia is used to identify the precipitate.

Ag+ (aq) + X- (aq) → AgX (s)

Question 8

What colour precipitates can be formed from a halide test?

Answer 8

AgCl - White precipitate
AgBr - Cream precipitate
AgI - Yellow precipitate

Question 9

What is the optimal order of anion tests?

Answer 9

Carbonate → Sulfate → Halide

Question 10

How can one test for ammonium ions in solution?

Answer 10

• Add NaOH (aq) to the solution and warm the mixture
• Test for any gas evolved with damp red litmus paper
• If the litmus paper turns blue, the gas is ammonia and NH4+ ions are present.

NH4+ + OH- → NH3 + H2O

Question 11

What is the solubility of silver halides in ammonia?

Answer 11

AgCl - Dilute = Yes, Conc. = Yes
AgBr - Dilute = No, Conc. = Yes
AgI - Dilute = No, Conc, = No