State and explain the trend in the reducing ability of the halide ions as we move down group 7.

The reducing ability of halide ions increases as we move down group 7.


This is because:

  1. As you go down the group, ionic radius and shielding increase (which outweighs the increased nuclear charge).
  2. This means there is a weaker electrostatic attraction between the nucleus and the electron it is trying to lose.
  3. This means their tendency to lose electrons and form atoms increases.

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Explain whether the halide ions act as oxidising or reducing agents in redox reactions.

Halide ions act as reducing agents in redox reactions because they lose electrons and are themselves oxidised.

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What are the colours of silver chloride, silver bromide and silver iodide precipitates?

Silver chloride is white.

Silver bromide is cream.

Silver iodide is yellow.

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What is the ionic equation, including state symbols, for the reaction between aqueous chloride ions and aqueous silver ions?

Cl-(aq) + Ag+(aq) ➔ AgCl(s)

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In the halide ion test, why is the silver nitrate solution acidified before use?

To remove any ions such as CO32- or OH- that would interfere with the test as white precipitates of silver carbonate or silver hydroxide might form which would give a false-positive result.

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What happens when aqueous Ag+ ions and dilute NH3 solution are added sequentially to a a solution of chloride ions?

Addition of Ag+: White precipitate of silver chloride forms. 

Addition of NH3: Precipitate redissolves to form a colourless solution.

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What happens when dilute NH3 solution and concentrated NH3 solution are added sequentially to a suspension of silver bromide?

Addition of dilute NH3: No change.

Addition of concentrated NH3: Cream precipitate redissolves to form a colourless solution.

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What are the changes in oxidation numbers of sulfur in the reactions between Cl-, Br- and I- ions with concentrated sulfuric acid?

Cl- ions: Oxidation number of sulfur does not change.

Br- ions: Oxidation number of sulfur decreases from +6 to +4 (in SO2).

I- ions: Oxidation number of sulfur decreases from +6 to +4 (in SO2), to 0 (in S) and to -2 (in H2S).

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When solid sodium chloride, sodium bromide, and sodium iodide react with concentrated sulfuric acid, what are the two common products formed in each reaction?

  1. All three reactions produce solid sodium hydrogensulfate (NaHSO4).
  2. Each reaction also produces steamy fumes of the corresponding hydrogen halide gas (HCl, HBr, or HI).

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Which halide ions are strong enough reducing agents to reduce sulfuric acid to sulfur dioxide in the reactions with concentrated sulfuric acid?

Bromide and iodide ions.

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Describe what happens in, and give the equation for, the reaction between hydrogen bromide gas and concentrated sulfuric acid.

Orange bromine vapour is produced:

2HBr(g) + H2SO4(aq) ➔ Br2(g) + SO2(g) + 2H2O(l)

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Describe what happens in, and give the equations for, the reactions between hydrogen iodide gas and conentrated sulfuric acid.

1Violet iodine vapour is produced:

2HI(g) + H2SO4(aq) ➔ I2(g) + SO2(g) + 2H2O(l)


2Yellow solid sulfur is produced:

6HI(g) + H2SO4(aq) ➔ 3I2(g) + S(s) + 4H2O(l)


3Hydrogen sulfide gas is produced which produces a rotten egg smell:

8HI(g) + H2SO4(aq) ➔ 4I2(g) + H2S(g) + 4H2O(l)

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What happens when aqueous Ag+ ions and concentrated NH3 solution are added sequentially to a solution of iodide ions?

Addition of Ag+: Yellow precipitate of silver iodide forms.

Addition of NH3: No further change.

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Which halide ion (F-, Cl-, Br-, or I-) is the most powerful reducing agent?

I-

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What is the equation, including state symbols, for the reaction between solid sodium chloride and concentrated sulfuric acid?

NaCl(s) + H2SO4(aq) ➔ NaHSO4(s) + HCl(g)

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