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Chemistry 20

Chemistry 20 · Worksheets

Final exam challenge

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

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Final exam challenge

Chemistry 20 · maddyhelps.com

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

  1. When 2.0 mol of H₂ reacts with 1.5 mol of O₂ by 2H₂ + O₂ → 2H₂O, the amount of water formed is

    1. a) 3.5 mol
    2. b) 1.5 mol, with O₂ limiting
    3. c) 2.0 mol, with H₂ limiting
    4. d) 3.0 mol, with O₂ limiting

  2. Decomposing 0.500 mol of CaCO₃ by CaCO₃ → CaO + CO₂ releases a volume of CO₂ at SATP of

    1. a) 24.8 L
    2. b) 11.2 L
    3. c) 0.500 L
    4. d) 12.4 L

  3. The pH of 0.010 mol/L NaOH is

    1. a) 12
    2. b) 10
    3. c) 2
    4. d) 1.0 × 10⁻¹²

  4. Molar concentration is measured in

    1. a) L/mol
    2. b) g/L
    3. c) mol/L
    4. d) mol

  5. The molar volume of an ideal gas at SATP is

    1. a) 24.8 L/mol
    2. b) 101.3 L/mol
    3. c) 22.4 L/mol
    4. d) 24.8 mL/mol

  6. The mass of 0.250 mol of NaCl is about

    1. a) 0.250 g
    2. b) 14.6 g
    3. c) 234 g
    4. d) 58.4 g

  7. The formula for sodium chloride is

    1. a) NaCl₂
    2. b) Na₂Cl
    3. c) Na₂Cl₂
    4. d) NaCl

  8. The name of N₂O₄ is

    1. a) dinitrogen tetroxide
    2. b) dinitrogen tetraoxide
    3. c) nitrogen(IV) oxide
    4. d) nitrogen tetroxide

  9. A solution in which [H₃O⁺] = 1.0 × 10⁻⁵ mol/L has a pH of

    1. a) 5
    2. b) 0.00001
    3. c) 9
    4. d) −5

  10. In a 0.10 mol/L solution of Na₂SO₄, the concentration of sodium ions is

    1. a) 0.05 mol/L
    2. b) 0.10 mol/L
    3. c) 0.20 mol/L
    4. d) 0.40 mol/L

Answer key · Final exam challenge

Chemistry 20 · maddyhelps.com

  1. c) 2.0 mol, with H₂ limiting — 2.0 mol of H₂ needs only 1.0 mol of O₂, and 1.5 mol is available, so hydrogen runs out first. The 1:1 ratio of H₂ to H₂O then gives 2.0 mol of water, and 0.5 mol of O₂ is left over.
  2. d) 12.4 L — The ratio is 1:1, so 0.500 mol of CO₂ forms, and V = nV_m = (0.500)(24.8) = 12.4 L. Using 22.4 L/mol here would be answering for STP, which is a different set of conditions.
  3. a) 12 — Sodium hydroxide is a strong base, so [OH⁻] = 0.010 mol/L and pOH = 2. Then pH = 14 − 2 = 12. Taking the logarithm of the concentration and stopping there gives 2, which is the pOH, not the pH.
  4. c) mol/L — Molar concentration is amount of solute per litre of solution, so mol/L. Grams per litre is a concentration too, but it is not molar concentration and cannot be used directly in stoichiometry.
  5. a) 24.8 L/mol — SATP is 25 °C and 100 kPa, giving 24.8 L/mol. The familiar 22.4 L/mol is the value at STP, 0 °C and 101.325 kPa. Alberta questions usually specify which, and the two are not interchangeable.
  6. b) 14.6 g — m = nM = (0.250)(58.44) ≈ 14.6 g. A quarter of a mole should weigh about a quarter of the molar mass, which is a quick way to check the arithmetic went the right way.
  7. d) NaCl — Sodium forms Na⁺ and chlorine forms Cl⁻. One of each balances the charge, so the formula unit is NaCl. Ionic formulas are always the simplest whole-number ratio.
  8. a) dinitrogen tetroxide — Both elements take prefixes in a molecular compound: di- for two nitrogens and tetr- for four oxygens. The a is dropped before the vowel, giving tetroxide rather than tetraoxide.
  9. a) 5 — pH = −log[H₃O⁺] = −log(10⁻⁵) = 5. The minus sign in the definition is what keeps everyday pH values positive.
  10. c) 0.20 mol/L — Each formula unit releases two Na⁺ and one SO₄²⁻, so the sodium concentration is twice the concentration of the compound. Ion concentrations follow the subscripts in the formula.