Topic 8C and 8D (Group 7 and titrations)

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Last updated 11:57 AM on 10/8/26
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8 Terms

1
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A reducing agent is a chemical species that donate/lose electrons to another substance during a redox reaction

What is the trend in strength of reducing agent for group 7?

  • Iodide is strongest reducing agent among halides

  • brominde is stronger reducing agent than chloride

  • chloride is weaker reducing agent than bromide

    I > Br > Cl

(flouride is not a reducing agent in normal conditions)

- as size of halide ions increaase down the group

[thats why Br- and I- undergoes redox and gets oxidized by H2SO4 but Cl- does not, it just undegoes acid base reaction )


2
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Explain the trend in reactivity in group 7

  • reactivity decreases down the group

    so flourine is more reactive than chlorine, while chlorine is more reactive than bromine and so on…

    F > Cl > Br > I

  • because atomic size increases down the group, outershell electron gets further away from the nucleus and are more shielded


3
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Explain the test for Halide ions

  • add nitric acid
    (to test for co32- or remove Co32- ion)

  • add silver nitrate solution
    Cl- = white precipitate
    Br- = pale cream precipitate
    I- = yellow precipitate


  • Add dilute amonnia solution to precipate
    if precipate dissolves in dilute ammonia = Cl- ions present

  • add concentrated ammonia solution to precipitate:
    if precipitate dissolves = Br- ions present
    (Cl- also dissolves in conc. ammonia solution)

    If precipitate doesn’t dissolve in dilute or concentrated ammonia solution → I- ions present


<ul><li><p><strong>add nitric acid </strong><br>(to test for co32- or remove Co32- ion)<br></p></li><li><p><strong>add silver nitrate solution</strong><br><strong>Cl- = white precipitate</strong><br><strong>Br- = pale cream precipitate</strong><br><strong>I- = yellow precipitate</strong><br><br></p></li><li><p><strong>Add <mark data-color="yellow" style="background-color: yellow; color: inherit;">dilute amonnia solution</mark> to precipate</strong><br><strong>if <u>precipate dissolves in dilute ammonia</u> =<mark data-color="yellow" style="background-color: yellow; color: inherit;"> Cl- ions</mark> present</strong><br></p></li><li><p>add <mark data-color="yellow" style="background-color: yellow; color: inherit;">concentrated ammonia solution</mark> to precipitate:<br>if precipitate dissolves = <strong><mark data-color="yellow" style="background-color: yellow; color: inherit;">Br- ions</mark> present </strong><br><strong>(Cl- also dissolves in conc. ammonia solution)</strong><br><br><strong>If precipitate doesn’t dissolve in dilute or concentrated ammonia solution → I- ions present</strong><br></p></li></ul><p></p>
4
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KCl/ NaCl (s) + H2SO4 —> NaHSO4 + HCl (g)

whats the observation ?

misty fumes

5
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KBr/ NaBr (s) + H2SO4 (l) → NaHSO4 + HBr(g)

2HBr (g) + H2SO4 (l) → Br2 + SO2 + 2H20

misty fumes
brown fumes
colorless gas with choking smell

6
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7
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purple solution

8
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iodine color in water solution =

iodine color in (non-polar) organic solvent solution =

iodine color in (polar) organic solvent solution =

iodine color in water solution = brown

iodine color in (non-polar) organic solvent solution = purple

iodine color in (polar) organic solvent solution = brown