Question 20 of 31intermediate🔧 ApplyLong Answer5 marks

Justify giving reactions that among halogens, fluorine is the best oxidant and among hydrohalic compounds, hydroiodic acid is the best reductant.

Correct Answer

Among halogens, the power of elements as oxidising agents decreases as we move down from fluorine to iodine in group 17. This makes fluorine the best oxidant. It is so reactive that it can replace chloride, bromide, and iodide ions in solution. In fact, fluorine is so reactive that it attacks water and displaces the oxygen of water, as shown in the following reactions:

H2O(s)+F2(g)→HF(g)+HOF(g)H_2O(s) + F_2(g) \rightarrow HF(g) + HOF(g)

2F2(g)+2OH−(aq)→2F−(aq)+OF2(g)+H2O(l)2F_2(g) + 2OH^- (aq) \rightarrow 2F^- (aq) + OF_2(g) + H_2O(l)

Furthermore, being the most electronegative element, fluorine cannot exhibit any positive oxidation state and does not show a disproportionation tendency.

Regarding hydrohalic compounds, as the oxidising power of halogens decreases down the group from fluorine to iodine, the reducing character of their corresponding halides increases. Consequently, among hydrohalic compounds, hydroiodic acid acts as the best reductant.

Exercise: EXERCISES | Q: 7.15 | (Page Page 19)
For More Understanding

Explanation

The textbook context explains that the oxidising power of halogens decreases down Group 17, making fluorine the strongest oxidant. It provides specific reactions where fluorine attacks water and displaces oxygen, highlighting its high reactivity. The context also notes fluorine's inability to show positive oxidation states or disproportionate. For hydroiodic acid, the context establishes the trend of decreasing oxidising power down the group, which inversely implies an increasing reducing power for the corresponding hydrohalic acids, making hydroiodic acid the best reductant.

Solution Steps

  1. Step 1: State the trend of oxidising power among halogens: The power of halogens as oxidising agents decreases down the group from fluorine to iodine.

  2. Step 2: Justify fluorine as the best oxidant: Fluorine is highly reactive and can replace chloride, bromide, and iodide ions in solution. It also attacks water and displaces oxygen.

  3. Step 3: Provide reactions for fluorine: H2O(s)+F2(g)→HF(g)+HOF(g)H_2O(s) + F_2(g) \rightarrow HF(g) + HOF(g) and 2F2(g)+2OH−(aq)→2F−(aq)+OF2(g)+H2O(l)2F_2(g) + 2OH^- (aq) \rightarrow 2F^- (aq) + OF_2(g) + H_2O(l).

  4. Step 4: Mention fluorine's electronegativity: As the most electronegative element, it cannot show a positive oxidation state or disproportionate.

  5. Step 5: Relate the trend to hydrohalic compounds: Since oxidising power decreases down the group, the reducing power of hydrohalic acids increases, making hydroiodic acid the best reductant.

PreviousNext