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Chemistry 30

Chemistry 30 · Worksheets

Cumulative review

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

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Cumulative review

Chemistry 30 · maddyhelps.com

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  1. A reaction releases energy to its surroundings. This reaction is

    1. a) exothermic, and its ΔH is negative
    2. b) endothermic, and its ΔH is positive
    3. c) endothermic, and its ΔH is negative
    4. d) exothermic, and its ΔH is positive

  2. A ketone differs from an aldehyde because its carbonyl group is

    1. a) bonded to carbons on both sides, rather than at the end of the chain
    2. b) always attached to a benzene ring
    3. c) a double bond between two carbons
    4. d) bonded to a hydroxyl group

  3. In the cell notation Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s), the zinc electrode is the

    1. a) anode, where oxidation occurs
    2. b) cathode, where reduction occurs
    3. c) anode, where reduction occurs
    4. d) salt bridge

  4. As a voltaic cell operates, the mass of the anode

    1. a) decreases, because the metal is reduced
    2. b) stays the same, because only electrons move
    3. c) increases, because metal ions plate onto it
    4. d) decreases, because the metal is oxidized into solution

  5. How much heat is absorbed when 100.0 g of water is warmed from 20.0 °C to 30.0 °C? (c = 4.19 J/(g·°C))

    1. a) 12.6 kJ
    2. b) 0.419 kJ
    3. c) 41.9 kJ
    4. d) 4.19 kJ

  6. Adding an inert gas such as argon to a gaseous equilibrium at constant volume

    1. a) shifts the equilibrium toward fewer moles of gas
    2. b) causes no shift, because the concentrations of the reacting gases are unchanged
    3. c) shifts the equilibrium toward the products
    4. d) increases K

  7. The conjugate base of H₂CO₃ is

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

  8. A reaction with K = 1 × 10⁶ at equilibrium

    1. a) strongly favours the reactants
    2. b) cannot reach equilibrium
    3. c) strongly favours the products
    4. d) has equal amounts of reactants and products

  9. Adding a catalyst to a reaction changes the

    1. a) neither one
    2. b) both the activation energy and ΔH
    3. c) activation energy, but not ΔH
    4. d) ΔH, but not the activation energy

  10. The purpose of the salt bridge in a voltaic cell is to

    1. a) let ions move between the half-cells so the solutions stay electrically neutral
    2. b) supply the energy that drives the reaction
    3. c) keep the two solutions from touching at all
    4. d) carry electrons from one half-cell to the other

Answer key · Cumulative review

Chemistry 30 · maddyhelps.com

  1. a) exothermic, and its ΔH is negative — Energy leaving the system means the products hold less enthalpy than the reactants, so ΔH = H(products) − H(reactants) is negative. Exothermic reactions feel warm because the energy ends up in the surroundings.
  2. a) bonded to carbons on both sides, rather than at the end of the chain — Both families contain C=O. In an aldehyde it sits at the end of the chain with a hydrogen attached; in a ketone it is between two carbon atoms.
  3. a) anode, where oxidation occurs — Cell notation is written anode on the left, cathode on the right, with the double line for the salt bridge. So zinc is oxidized and copper ions are reduced.
  4. d) decreases, because the metal is oxidized into solution — Oxidation at the anode turns solid metal into ions that dissolve, so the electrode gets thinner. The cathode gains mass as ions plate onto it — a standard way to identify the electrodes from experimental data.
  5. d) 4.19 kJ — q = mcΔT = (100.0 g)(4.19 J/(g·°C))(10.0 °C) = 4190 J = 4.19 kJ. ΔT is the change in temperature, not the final temperature.
  6. b) causes no shift, because the concentrations of the reacting gases are unchanged — Total pressure rises, but the partial pressures and concentrations of the species in the equilibrium expression do not change, so there is nothing for the system to respond to. Pressure only matters when it is caused by a volume change.
  7. b) 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.
  8. c) strongly favours the products — K is products over reactants, so a very large K means the numerator dominates — at equilibrium the mixture is almost all product. A very small K means almost all reactant.
  9. c) activation energy, but not ΔH — A catalyst provides a lower-energy pathway, so the hump gets shorter. The reactants and products are unchanged, so the difference between them — ΔH — stays exactly the same.
  10. a) let ions move between the half-cells so the solutions stay electrically neutral — As the cell runs, one half-cell builds up positive charge and the other negative. Ions migrating through the salt bridge cancel that build-up; without it the charge separation stops the reaction almost immediately.