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Chemistry 30

Chemistry 30 · Worksheets

Mixed review · Equilibrium and acids

Ten questions of mixed difficulty, covering Acids and bases, Equilibrium. Print it, or work through it on screen — the answer key starts on its own page.

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Mixed review · Equilibrium and acids

Chemistry 30 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. Adding a catalyst to a system at equilibrium

    1. a) increases the value of K
    2. b) shifts the equilibrium toward the reactants
    3. c) shifts the equilibrium toward the products
    4. d) does not shift the equilibrium, but it is reached sooner

  2. The reaction of an acid with a base produces

    1. a) a gas and water
    2. b) a salt and water
    3. c) hydrogen only
    4. d) an acid and a base

  3. The conjugate base of H₂CO₃ is

    1. a) H₃CO₃⁺
    2. b) H₂CO₃
    3. c) HCO₃⁻
    4. d) CO₃²⁻

  4. At 25 °C, pH + pOH =

    1. a) 1.00
    2. b) 14.00
    3. c) 7.00
    4. d) 10.00

  5. A reaction has K = 4.0 × 10⁻³ at a given temperature. At equilibrium the mixture

    1. a) contains mostly products
    2. b) has completely reacted
    3. c) contains mostly reactants
    4. d) contains equal amounts of each

  6. For N₂(g) + 3H₂(g) ⇌ 2NH₃(g), increasing the pressure by reducing the volume shifts the equilibrium

    1. a) left, because ammonia is a gas
    2. b) neither way, since pressure does not affect equilibrium
    3. c) left, toward the side with more moles of gas
    4. d) right, toward the side with fewer moles of gas

  7. According to the Arrhenius definition, an acid is a substance that

    1. a) donates an electron pair
    2. b) produces hydrogen ions in water
    3. c) produces hydroxide ions in water
    4. d) accepts a proton

  8. A solution has [OH⁻] = 1.0 × 10⁻⁵ mol/L. Its pH at 25 °C is

    1. a) −5.00
    2. b) 9.00
    3. c) 14.00
    4. d) 5.00

  9. A 0.100 mol/L solution of a weak acid has a pH of 2.88. Its Ka is closest to

    1. a) 1.3 × 10⁻³
    2. b) 2.9 × 10⁻³
    3. c) 1.0 × 10⁻⁷
    4. d) 1.8 × 10⁻⁵

  10. At 25 °C, a solution with a pH of 3.0 is

    1. a) acidic
    2. b) impossible
    3. c) basic
    4. d) neutral

Answer key · Mixed review · Equilibrium and acids

Chemistry 30 · maddyhelps.com

  1. d) does not shift the equilibrium, but it is reached sooner — A catalyst speeds the forward and reverse reactions equally, so the position of equilibrium is untouched. It changes how fast you get there, not where you end up.
  2. b) a salt and water — Neutralization pairs H⁺ with OH⁻ to make water, leaving the remaining ions as a salt. HCl + NaOH gives NaCl and H₂O.
  3. c) HCO₃⁻ — A conjugate base is what remains after the acid donates exactly one proton: H₂CO₃ − H⁺ = HCO₃⁻. Removing two protons gives the carbonate ion, which is the conjugate base of HCO₃⁻ instead.
  4. b) 14.00 — Water's ion product gives [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C, which becomes pH + pOH = 14.00 in logarithmic form. It is the quickest route between the two scales.
  5. c) contains mostly reactants — K far below 1 means the denominator — the reactants — dominates. The reaction barely proceeds before it settles, which is why a small K is described as favouring reactants.
  6. d) right, toward the side with fewer moles of gas — Four moles of gas on the left, two on the right. Squeezing the system favours the side that relieves the pressure by occupying fewer moles — the right. If both sides had equal moles of gas, pressure would have no effect.
  7. b) produces hydrogen ions in water — Arrhenius defined acids and bases by what they release in water: H⁺ for an acid, OH⁻ for a base. Bronsted-Lowry broadens this to proton donors and acceptors, which covers reactions outside water.
  8. b) 9.00 — pOH = −log(1.0 × 10⁻⁵) = 5.00, so pH = 14.00 − 5.00 = 9.00. Answering 5.00 is forgetting to convert pOH to pH — and a hydroxide concentration that high should give a basic pH.
  9. d) 1.8 × 10⁻⁵ — [H₃O⁺] = 10⁻²·⁸⁸ = 1.3 × 10⁻³ mol/L. Ka = [H₃O⁺]² ÷ [HA] = (1.3 × 10⁻³)² ÷ 0.100 ≈ 1.8 × 10⁻⁵. Stopping at the hydronium concentration gives the 1.3 × 10⁻³ distractor.
  10. a) acidic — Below 7 is acidic at 25 °C, 7 is neutral and above 7 is basic. Each whole number is a factor of ten in hydrogen ion concentration, so pH 3 is a hundred times more acidic than pH 5.