maddyhelps

Chemistry 30

Chemistry 30 · Worksheets

Electrochemical cells

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

All worksheets

Electrochemical cells

Chemistry 30 · maddyhelps.com

Name
Date
Score
/ 10

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

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

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

  2. Attaching a block of zinc to a steel boat hull protects the steel because zinc

    1. a) is harder than iron, so it shields the hull
    2. b) is more easily oxidized than iron, so it corrodes instead
    3. c) prevents oxygen from dissolving in the water
    4. d) reduces the iron ions back to iron

  3. A voltaic cell converts

    1. a) electrical energy into chemical energy
    2. b) heat into chemical energy
    3. c) electrical energy into heat only
    4. d) chemical energy into electrical energy

  4. Which statement about an electrolytic cell is correct?

    1. a) It needs an external power supply, and its anode is the positive electrode
    2. b) It runs spontaneously, and its cathode is negative
    3. c) It needs an external power supply, and its anode is the negative electrode
    4. d) It runs spontaneously, and its anode is positive

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

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

  6. A cell is built from Ag⁺/Ag (E° = +0.80 V) and Ni²⁺/Ni (E° = −0.26 V). The cell potential and anode are

    1. a) +0.54 V, with nickel as the anode
    2. b) −1.06 V, with silver as the anode
    3. c) +1.06 V, with silver as the anode
    4. d) +1.06 V, with nickel as the anode

  7. A current of 2.00 A flows for 30.0 min through a solution of Cu²⁺. The mass of copper deposited is closest to

    1. a) 1.19 g
    2. b) 0.59 g
    3. c) 4.74 g
    4. d) 2.37 g

  8. In any electrochemical cell, oxidation occurs at the

    1. a) salt bridge
    2. b) anode
    3. c) cathode
    4. d) electrolyte

  9. In a voltaic cell, electrons travel through the external wire from the

    1. a) salt bridge to the anode
    2. b) anode to the cathode
    3. c) cathode to the anode
    4. d) solution to the electrodes

  10. How many moles of electrons are needed to produce 1 mol of aluminum from Al³⁺?

    1. a) 2 mol
    2. b) 3 mol
    3. c) 27 mol
    4. d) 1 mol

Answer key · Electrochemical cells

Chemistry 30 · maddyhelps.com

  1. b) 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.
  2. b) is more easily oxidized than iron, so it corrodes instead — This is cathodic protection with a sacrificial anode. Zinc has the lower reduction potential, so it gives up electrons more readily and is consumed while the iron is spared.
  3. d) chemical energy into electrical energy — A voltaic (galvanic) cell uses a spontaneous redox reaction to push electrons through a circuit — a battery. An electrolytic cell does the reverse, using electricity to force a non-spontaneous reaction.
  4. a) It needs an external power supply, and its anode is the positive electrode — Electrolytic cells drive non-spontaneous reactions, so a power supply is required, and it makes the anode positive. In a voltaic cell the anode is the negative electrode — the one sign difference worth memorizing.
  5. c) 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.
  6. d) +1.06 V, with nickel as the anode — Silver has the higher reduction potential, so it is reduced at the cathode and nickel is oxidized at the anode: E°cell = 0.80 − (−0.26) = +1.06 V. Adding the two potentials instead of subtracting gives 0.54 V.
  7. a) 1.19 g — q = It = (2.00 A)(1800 s) = 3600 C. Moles of electrons = 3600 ÷ 96500 = 0.0373 mol. Cu²⁺ needs 2 electrons each, so 0.0187 mol of Cu × 63.55 g/mol = 1.19 g. Forgetting to divide by 2 gives the 2.37 g distractor.
  8. b) anode — Oxidation always happens at the anode and reduction at the cathode, in both voltaic and electrolytic cells. An old memory hook: AN OX and RED CAT.
  9. b) anode to the cathode — Electrons are released by the oxidation at the anode and consumed by the reduction at the cathode, so they flow anode to cathode through the wire. Ions, not electrons, move through the solution and salt bridge.
  10. b) 3 mol — Al³⁺ + 3e⁻ → Al, so each aluminum atom needs three electrons. That is why producing aluminum by electrolysis uses so much electricity.