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A Levelchemistry · Topic 11

Chemistry Paper 2 Topic 11: Group 17

Practice exam questions on halogens, halide reducing trends with sulfuric acid, silver halide testing, and disproportionation reactions.

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About Group 17

Group 17 (the halogens) explores the chemistry of fluorine, chlorine, bromine, and iodine. This topic covers physical trends such as volatility and London dispersion forces, the decreasing oxidizing power of the halogens, and the increasing reducing power of halide ions in reactions with concentrated sulfuric acid. It also details qualitative halide testing using silver nitrate and aqueous ammonia, the thermal stability of hydrogen halides, and the disproportionation reactions of chlorine in water purification and bleach production.

Why Is Group 17 Important?

Group 17 illustrates essential non-metal redox chemistry. In Cambridge Paper 2, examiners frequently test qualitative observations, redox balancing for halide reactions with concentrated H₂SO₄, and the commercial importance of chlorine disproportionation in water sanitation and sodium chlorate manufacturing.

Skills Tested In This Topic

Students are tested on explaining boiling point trends using London dispersion forces, rationalizing the decreasing thermal stability of hydrogen halides (HF to HI) via H-X bond energies, writing balanced redox equations and listing observations for solid halides reacting with concentrated H₂SO₄, and identifying halide ions with silver nitrate followed by dilute and concentrated ammonia.

How This Topical Paper Helps

Practicing topical past paper questions trains students to remember exact color changes (e.g. orange organic layer for Br₂, purple for I₂), distinguish between acid-base and redox reactions of sulfuric acid, and write flawless disproportionation equations under cold and hot conditions.

Exam Preparation Tips

For reactions with concentrated H₂SO₄, remember that NaCl undergoes only acid-base reaction (steamy HCl fumes), NaBr undergoes acid-base and partial redox (forming brown Br₂ vapor and choking SO₂ gas), and NaI undergoes extensive redox (forming purple I₂ vapor, yellow solid S, and rotten-egg smelling H₂S gas).

Why Practice Past Paper Questions?

Cambridge Paper 2 questions often present unknown halide salts in experimental scenarios requiring step-by-step deduction. Practicing with topical booklets builds analytical reasoning and ensures quick mastery of qualitative analysis marks.

Quick Answer

Group 17 in AS Level Chemistry covers halogen physical properties, decreasing oxidizing strength down the group, increasing reducing power of halide ions in reactions with concentrated H₂SO₄, silver halide precipitation tests (AgCl, AgBr, AgI) with dilute and concentrated ammonia, thermal stability of hydrogen halides, and chlorine disproportionation with cold (forming NaClO) and hot (forming NaClO₃) aqueous NaOH. Topical past paper practice sharpens redox equation balancing and qualitative observation accuracy in Cambridge Paper 2.

How To Revise Using This Paper

  • Learn physical properties and colors: Cl₂ (pale green gas), Br₂ (red-brown liquid), I₂ (grey-black solid, purple vapor).
  • Explain boiling point increase down Group 17 in terms of increasing electron count and stronger London dispersion forces.
  • Understand halide reducing power: I⁻ > Br⁻ > Cl⁻ > F⁻ (larger ionic radius → weaker nuclear hold on outer electrons → more easily oxidized).
  • Memorize reactions with concentrated H₂SO₄: NaCl produces HCl; NaBr produces HBr, Br₂, and SO₂; NaI produces HI, I₂, SO₂, S, and H₂S.
  • Master halide precipitation: AgCl (white ppt, dissolves in dilute NH₃), AgBr (cream ppt, dissolves in concentrated NH₃), AgI (yellow ppt, insoluble in concentrated NH₃).
  • Learn hydrogen halide thermal stability: HF > HCl > HBr > HI (decreasing H-X bond energy makes HI easiest to decompose).
  • Memorize chlorine disproportionation: cold dilute NaOH produces NaCl + NaClO + H₂O; hot concentrated NaOH produces 5NaCl + NaClO₃ + 3H₂O.

Summary

Group 17 covers the halogens (Cl₂, Br₂, I₂), focusing on halogen oxidizing power, halide ion reducing strength with concentrated sulfuric acid, silver halide precipitation and solubility in ammonia, hydrogen halide thermal stability, and chlorine disproportionation reactions. Revision should prioritize writing balanced redox equations, predicting precise experimental observations, and mastering qualitative analysis criteria. Topical past paper practice ensures high marks in Cambridge AS Chemistry Paper 2.

Frequently Asked Questions

Group 17 (the halogens) covers physical trends of halogens (volatility, color, boiling points), halogen oxidizing power, halide ion reducing strength with concentrated H2SO4, halide precipitation tests with acidified AgNO3 and NH3(aq), thermal stability of hydrogen halides, and chlorine disproportionation reactions.

Group 17 is heavily examined in Paper 2. Cambridge examiners frequently test redox half-equations and observations for solid sodium halides reacting with concentrated sulfuric acid, distinguishing silver halide precipitates with dilute/concentrated ammonia, and writing disproportionation equations with cold and hot NaOH.

While displacement and color trends are straightforward, multi-stage redox reactions between concentrated H2SO4 and sodium iodide (producing SO2, S, and H2S) and remembering exact conditions for cold versus hot alkali disproportionation often challenge students.

Practice writing full redox equations for H2SO4 reactions with NaCl, NaBr, and NaI, memorize the solubility behavior of AgCl, AgBr, and AgI in dilute and concentrated aqueous ammonia, and review thermal stability of hydrogen halides linked to H-X bond energies.

Group 17 questions typically account for 7 to 11 marks in Paper 2, often appearing as structured questions combining qualitative tests, redox balancing, and oxidation state calculations.

Yes. Topical past papers train you to identify specific examiner observation keywords-such as steamy fumes (HCl/HBr/HI), red-brown liquid/vapor (Br2), purple vapor/yellow solid/bad egg smell (I2/S/H2S), and white/cream/yellow silver halide precipitates.

Yes. Repetition ensures quick recall of oxidation states in chlorate ions (+1 in NaClO vs +5 in NaClO3) and prevents confusing the oxidizing power of halogens with the reducing power of halide ions.

Common mistakes include stating chlorine oxidizes H2SO4, confusing the reactions of cold dilute NaOH (forms NaClO) with hot concentrated NaOH (forms NaClO3), forgetting that AgI is insoluble in concentrated NH3, and writing incomplete redox products for NaI + H2SO4.

Allocate 3 focused study sessions to master halide testing, sulfuric acid redox reactions, and disproportionation equations before moving to Nitrogen and Sulfur.

Yes. This topical PDF compiles authentic Cambridge structured questions with official mark schemes, allowing independent learners to test their knowledge of observations, equations, and redox mechanisms thoroughly.