Chemistry Clarity · chemistryclarity.com

Acid–Base Properties of Salts: Flashcards

Revise salt hydrolysis, predicting acidic, basic and neutral salts, Ka × Kb = Kw and the pH of salt solutions.

10 cardsIntermediate

10 cards

  1. Question
    What is hydrolysis of a salt?
    Answer

    The reaction of an ion with water, producing H₃O⁺ or OH⁻ and changing the pH.

  2. Question
    Is a salt of a strong acid and a strong base acidic, basic or neutral?
    Answer

    Neutral (pH 7), e.g. NaCl, KNO₃.

  3. Question
    Is a salt of a strong acid and a weak base acidic, basic or neutral?
    Answer

    Acidic, e.g. NH₄Cl: NH₄⁺ gives H⁺ to water.

  4. Question
    Is a salt of a weak acid and a strong base acidic, basic or neutral?
    Answer

    Basic, e.g. CH₃COONa: CH₃COO⁻ takes H⁺ from water, forming OH⁻.

  5. Question
    Which ions do not hydrolyse?
    Answer

    Conjugates of strong acids and bases: Cl⁻, Br⁻, I⁻, NO₃⁻, Na⁺, K⁺ (and other Group 1 ions).

  6. Question
    State the relationship between Ka and Kb for a conjugate pair.
    Answer

    Ka×Kb=Kw=1.0×10−14K_\text{a} \times K_\text{b} = K_\text{w} = 1.0 \times 10^{-14} at 25 °C

  7. Question
    Ka of ethanoic acid is 1.8 × 10⁻⁵. What is Kb of the ethanoate ion?
    Answer

    1.0 × 10⁻¹⁴ ÷ 1.8 × 10⁻⁵ = 5.6 × 10⁻¹⁰

  8. Question
    Why is the pH at the equivalence point of a weak acid–strong base titration above 7?
    Answer

    The solution contains the salt of the weak acid, whose anion is a weak base.

  9. Question
    Why are solutions of Al³⁺ or Fe³⁺ salts acidic?
    Answer

    The small, highly charged hydrated ions release H⁺ from their attached water molecules.

  10. Question
    Outline how to calculate the pH of 0.10 mol/L sodium ethanoate.
    Answer

    Kb = Kw/Ka → [OH⁻] ≈ √(Kb × C) → pOH → pH = 14.00 − pOH (answer 8.87).