Metal Aqua Ions: Acidity, Ligand Exchange and Precipitation · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Aqua ions, precipitates and tests

Science · Chemistry · ages 17-18
Name ______________________   Date ____________

  1. What do you see when sodium hydroxide meets copper(II) solution?

    • A blue solid falls out of solution
    • The solution turns colourless at once
    • Bubbles of brown gas rise up

  2. Why does a 3+ aqua ion give a more acidic solution than a 2+ one?

    • It carries more water molecules with it
    • It pulls harder on bound water and frees more H+
    • It reacts with air to make extra acid

  3. Zinc hydroxide redissolves in both excess ammonia and excess alkali.

    Circle one:   True   False

  4. An unknown gives a green precipitate that stays put in excess alkali. Which ion is it?

    • Chromium(III)
    • Aluminium
    • Iron(II)

  5. Copper hydroxide precipitate clears in excess ammonia. What colour does the solution turn?

    • Pale green
    • Deep blue
    • Brick red

  6. What colour change shows ligand exchange when concentrated HCl meets Cu2+ solution?

    • Pale blue to yellow-green as chloro ligands take over
    • Blue to colourless as copper metal plates out
    • Green to orange as the solution boils

  7. A student claims any 2+ aqua ion is more acidic than any 3+ one. What is the flaw?

    • Acidity is set by charge density, so 3+ pulls harder than 2+
    • Aqua ions are never acidic at all
    • Only temperature sets the acidity of aqua ions

  8. A student sees a green precipitate dissolve in excess alkali and names iron(II). What is wrong?

    • Iron(II) green stays put, so dissolving points to chromium(III)
    • Green precipitates never dissolve in anything
    • Iron(II) gives a blue precipitate, not a green one
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Aqua ions, precipitates and tests W1-mt_jrsKwNq1Oi-s1

  1. A blue solid falls out of solution · Blue copper(II) hydroxide precipitates: Cu2+ plus 2OH- gives Cu(OH)2.
  2. It pulls harder on bound water and frees more H+ · Higher charge density polarises the O-H bonds more, releasing more H+.
  3. True · Zinc sits in both lists: it clears in ammonia and in alkali. The sentence is true.
  4. Iron(II) · Chromium(III) green redissolves, while iron(II) green stays put.
  5. Deep blue · Excess ammonia swaps in as a ligand and the copper solution turns deep blue.
  6. Pale blue to yellow-green as chloro ligands take over · Water ligands swap for chloro ligands, giving yellow-green [CuCl4]2- from pale blue [Cu(H2O)6]2+.
  7. Acidity is set by charge density, so 3+ pulls harder than 2+ · Higher charge polarises bound water more and frees more H+, so 3+ beats 2+.
  8. Iron(II) green stays put, so dissolving points to chromium(III) · Dissolving in excess alkali fits chromium(III). Iron(II) would have stayed put.
Worksheet · LightMySky