Acid-Base Models Beyond Bronsted: Lewis, Solvents and Hard and Soft · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Acids without protons

Science · Chemistry · ages 19-20
Name ______________________   Date ____________

  1. Boron trifluoride reacts with ammonia with no proton moving. Which is the Lewis acid?

    • Ammonia, since it has the lone pair
    • Boron trifluoride, since it takes the lone pair
    • Neither, since no proton moves

  2. What makes a substance a Lewis acid?

    • It donates a proton
    • It accepts an electron pair
    • It releases hydroxide

  3. Hard acids bind most strongly to hard bases, and soft acids to soft bases.

    Circle one:   True   False

  4. A new metal ion is large and easily polarised. Which anion should bind it most strongly?

    • Iodide
    • Fluoride
    • Oxide

  5. Why is magnesium mined as a carbonate?

    • Magnesium is a hard acid paired with the hard carbonate base
    • Carbonate is the only anion in seawater
    • Magnesium cannot form any other salt

  6. Why does the water-based acid definition fail in liquid ammonia?

    • Ammonia has no atoms
    • Acids cannot dissolve in ammonia
    • Water is only one stage, and each solvent defines its own acid-base pair

  7. A soft metal ion such as mercury(I) binds most strongly to hard bases such as fluoride.

    Circle one:   True   False

  8. A student calls ammonia the Lewis acid in its reaction with boron trifluoride because ammonia owns the lone pair. What is the error?

    • Owning the pair makes ammonia the base, since acids take pairs
    • Boron trifluoride has no empty orbital
    • Lone pairs cannot form bonds
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Answer key

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

Acids without protons W1-mt_jarui-9yfx-s1

  1. Boron trifluoride, since it takes the lone pair · Boron trifluoride accepts the nitrogen lone pair, so it is the acid.
  2. It accepts an electron pair · Pair acceptance is the whole Lewis test for acids.
  3. True · Like prefers like in the hard and soft scheme.
  4. Iodide · A large polarisable ion is a soft acid, so it wants the soft iodide base.
  5. Magnesium is a hard acid paired with the hard carbonate base · The ore records the metal sitting beside its favourite partner.
  6. Water is only one stage, and each solvent defines its own acid-base pair · The solvent system view replaces water's actors with the solvent's own.
  7. False · Soft prefers soft, so mercury pairs with sulfide or iodide instead.
  8. Owning the pair makes ammonia the base, since acids take pairs · The giver of the pair is the base and the taker is the acid.
Worksheet · LightMySky