Chapter 12: Halogens – Comprehensive Exercise Solutions for Federal Board Students

Access detailed solutions to Chapter 12: Halogens from Federal Board Chemistry syllabus. Includes multiple-choice answers, short questions, and comprehensive explanations on reactivity, oxidizing power, and trends of halogens. Perfect for college students!

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Choose the Correct Answer

1. Which halogen has a greenish-yellow color?
   Answer: (b) Cl₂
   Explanation: Chlorine (Cl₂) gas is greenish-yellow in color and is commonly used in water treatment and as a bleaching agent.
2. Which halogen exists in a liquid state?
   Answer: (c) Br₂
   Explanation: Bromine (Br₂) is the only halogen that is a liquid at room temperature, and it has a reddish-brown color.
3. Which of the following is the strongest reducing agent?
   Answer: (d) I⁻
   Explanation: Iodide ion (I⁻) is the strongest reducing agent among halides because it easily donates electrons compared to other halides.
4. Oxidizing power of which halogen is highest?
   Answer: (a) F₂
   Explanation: Fluorine (F₂) is the most electronegative element and has the highest oxidizing power among halogens.
5. Which is the strongest acid?
   Answer: (b) HCl
   Explanation: Hydrochloric acid (HCl) is a strong acid due to its complete dissociation in water, unlike HF, which forms hydrogen bonds and is weaker.

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Give Short Answers

1. Give the order of oxidizing power of halogens.
   Answer:
   The oxidizing power of halogens decreases down the group:
   F₂ > Cl₂ > Br₂ > I₂
   Fluorine is the strongest oxidizing agent because it has the highest electronegativity and smallest atomic size.
2. How does the reactivity of halogens with hydrogen vary?
   Answer:
   The reactivity of halogens with hydrogen decreases down the group:
   F₂ > Cl₂ > Br₂ > I₂
   Fluorine reacts explosively with hydrogen, while iodine reacts slowly. This variation is due to the decreasing bond strength of hydrogen-halogen bonds down the group.
3. Why is the strength of HF different from HCl?
   Answer:
   HF is a weaker acid compared to HCl because of the strong hydrogen bonding in HF, which reduces its ability to dissociate completely in water. In contrast, HCl dissociates fully, making it a stronger acid.
4. Write reactions of sulfuric acid with NaCl and NaBr.
   Answer:
   • With NaCl:
     NaCl+H2SO4→HCl+NaHSO4NaCl + H₂SO₄ → HCl + NaHSO₄
     Produces hydrogen chloride gas.
   • With NaBr:
     NaBr+H2SO4→HBr+NaHSO4NaBr + H₂SO₄ → HBr + NaHSO₄
     Further oxidation occurs, producing bromine gas.
5. What is a disproportionation reaction?
   Answer:
   A disproportionation reaction is a redox reaction in which the same element is simultaneously oxidized and reduced.
   Example: Chlorine in water:
   Cl2+H2O→HCl+HOClCl₂ + H₂O → HCl + HOCl

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6. Explain the reactions of chlorine with sodium hydroxide.
   Answer:
   Chlorine reacts with NaOH to form a disproportionation reaction:
   2NaOH+Cl2→NaCl+NaClO+H2O2NaOH + Cl₂ → NaCl + NaClO + H₂O
   This forms sodium chloride and sodium hypochlorite, commonly used in bleach.
7. Describe the silver nitrate test for halide ions.
   Answer:
   • Add dilute nitric acid to remove carbonate or hydroxide impurities.
   • Add silver nitrate solution.
     • Chlorides (Cl⁻): White precipitate (AgCl)
     • Bromides (Br⁻): Cream precipitate (AgBr)
     • Iodides (I⁻): Yellow precipitate (AgI)
8. How does sulfuric acid react with halide ions?
   Answer:
   Sulfuric acid reacts differently with halides:
   • Cl⁻: Produces HCl gas.
   • Br⁻: Produces Br₂ and SO₂ due to redox reactions.
   • I⁻: Produces I₂ and H₂S due to stronger reduction.
9. Compare the strength of halogen acids.
   Answer:
   The strength of halogen acids increases as the bond strength decreases:
   HF < HCl < HBr < HI
   HI is the strongest because the bond dissociation energy is the lowest.
10. Evaluate the reactivity of halogens.
    Answer:
    Reactivity decreases down the group:
    F₂ > Cl₂ > Br₂ > I₂
    Fluorine reacts most vigorously due to its high electronegativity and small atomic radius.
11. Discuss trends in:

• Volatility of halogens: Decreases down the group due to increasing molecular size and van der Waals forces.
• Strength in halogen molecules: Bond strength decreases down the group due to increasing bond length.

12. Interpret the reactivity of halogens as oxidizing agents.
    Answer:
    Halogens are strong oxidizing agents because they gain electrons easily. Reactivity decreases as electronegativity and reduction potential decrease down the group.

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