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Chemistry 20

Chemistry 20 · Worksheets

Mixed review · Every calculation in the course

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

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Mixed review · Every calculation in the course

Chemistry 20 · maddyhelps.com

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

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

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

  2. The mass of 0.250 mol of NaCl is about

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

  3. A gas occupies 3.0 L at 200 kPa and 300 K. At 100 kPa and 400 K it occupies

    1. a) 4.5 L
    2. b) 6.0 L
    3. c) 1.5 L
    4. d) 8.0 L

  4. At the same temperature, the gas whose molecules have the greatest average speed is

    1. a) CO₂
    2. b) H₂
    3. c) Cl₂
    4. d) O₂

  5. In 2H₂ + O₂ → 2H₂O, the mole ratio of H₂ to H₂O is

    1. a) 2:3
    2. b) 1:1
    3. c) 1:2
    4. d) 2:1

  6. Diluting 50.0 mL of 2.00 mol/L solution to 200.0 mL gives a concentration of

    1. a) 0.500 mol/L
    2. b) 1.00 mol/L
    3. c) 0.125 mol/L
    4. d) 8.00 mol/L

  7. According to the kinetic molecular theory, the particles of an ideal gas

    1. a) attract each other strongly
    2. b) are closely packed and vibrate in place
    3. c) all move at exactly the same speed
    4. d) are in constant random motion and have negligible volume of their own

  8. One mole of any substance contains

    1. a) 6.02 × 10²³ grams
    2. b) 1 gram of particles
    3. c) 12 particles
    4. d) 6.02 × 10²³ particles

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

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

  10. Absolute zero is

    1. a) −100 °C
    2. b) −373.15 °C
    3. c) −273.15 °C
    4. d) 0 °C

Answer key · Mixed review · Every calculation in the course

Chemistry 20 · maddyhelps.com

  1. b) 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.
  2. a) 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.
  3. d) 8.0 L — The combined gas law gives V₂ = P₁V₁T₂/(T₁P₂) = (200)(3.0)(400)/[(300)(100)] = 8.0 L. Lower pressure and higher temperature both expand the gas, so an answer larger than 3.0 L is expected.
  4. b) H₂ — Same temperature means the same average kinetic energy, ½mv². The lightest molecules must therefore be moving fastest to carry the same energy, and hydrogen is by far the lightest here.
  5. b) 1:1 — The coefficients are both 2, which reduces to 1:1. Every two hydrogen molecules give two water molecules, so the amounts match even though the substances are different.
  6. a) 0.500 mol/L — Dilution does not change the amount of solute, so c₁V₁ = c₂V₂ and c₂ = (2.00)(50.0)/200.0 = 0.500 mol/L. Quadrupling the volume divides the concentration by four.
  7. d) are in constant random motion and have negligible volume of their own — The model treats particles as points that fly about at random and only interact by colliding. Real gases depart from it at high pressure and low temperature, where volume and attractions stop being negligible.
  8. d) 6.02 × 10²³ particles — Avogadro's number is a count, not a mass. A mole of carbon and a mole of lead contain the same number of atoms but weigh very different amounts.
  9. b) 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.
  10. c) −273.15 °C — It is the temperature at which particle motion would stop, and it is the zero of the Kelvin scale. Nothing colder exists, which is why gas law calculations have to use kelvins.