Strong and Weak Acids and the pH Scale · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Strong means split, not crowded

Science · Matter & Materials · ages 14-16
Name ______________________   Date ____________

  1. Which of these acids is weak?

    • Hydrochloric acid
    • Sulfuric acid
    • Ethanoic acid

  2. What does a strong acid do in water?

    • Ionises partly
    • Stays solid
    • Ionises fully

  3. A concentrated acid is always a strong acid.

    Circle one:   True   False

  4. Why does a strong acid react faster with magnesium than a weak acid of the same concentration?

    • It is hotter in the bottle
    • It floods the metal with more ions at once
    • It contains a catalyst

  5. An acid is diluted ten times. What happens to its pH?

    • It rises by one
    • It falls by one
    • It stays the same

  6. How can a concentrated weak acid have a higher pH than a dilute strong acid?

    • Weak acids hate water
    • The strong acid still releases more ions
    • pH ignores concentration

  7. Hydrochloric acid in water runs one way, while ethanoic acid sets up a balance.

    Circle one:   True   False

  8. Two solutions share pH 2. One is dilute strong acid, one is concentrated weak acid. Which holds more unreleased acid?

    • The dilute strong one
    • Both hold equal amounts
    • The concentrated weak one
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Answer key

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

Strong means split, not crowded W1-mt_Y4nSn5XH56-s1

  1. Ethanoic acid · Ethanoic acid splits only partly, so it is weak.
  2. Ionises fully · Strong means fully split: every hydrogen ion is released.
  3. False · Concentration counts particles while strength counts splitting. Separate dials.
  4. It floods the metal with more ions at once · Full splitting floods the metal with ions at once, so the reaction runs faster.
  5. It rises by one · Tenfold fewer hydrogen ions lift the pH by exactly one.
  6. The strong acid still releases more ions · pH counts released ions, and the dilute strong acid still releases more of them.
  7. True · Full splitting runs one way, while partial splitting sets up a balance.
  8. The concentrated weak one · The weak acid released only a fraction to reach pH 2, so most of it sits unreleased.
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