Electrolytic Cell Examples: 46 Problems with Answers

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Electrolytic Cell.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

An electrolytic cell uses an external power source to force a nonspontaneous redox reaction to occur. Electrical energy is converted into chemical change.

Instead of getting electricity from chemistry, you spend electricity to make chemistry happen.

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How to Use These Examples

Read the first worked example with the solution open so the structure is clear.
Try the practice problems before revealing each solution.
Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Electrolytic Cell starts by assigning oxidation and reduction, then traces electrons through the wire and ions through solution.

Common stuck point: Students often know a formula related to electrolytic cell but skip the recognition step: Am I tracking oxidation, reduction, electron flow, ions, electrodes, and whether the cell is spontaneous or driven? That leads to a correct-looking substitution attached to the wrong chemical model.

Sense of Study hint: Ask: Am I tracking oxidation, reduction, electron flow, ions, electrodes, and whether the cell is spontaneous or driven?

Worked Examples

Example 1

medium

A current of

1.50

A flows for

1.00

hour through aqueous

AgNO_3

. Find the mass of

Ag

deposited (

Ag = 108

g/mol).

Answer

6.04 g A g

First step

Charge:

Q = 1.50 \times 3600 = 5400

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Example 2

medium

How long must a

4.0

A current run to deposit

1.0

mol of copper from

Cu^{2+}

Example 3

medium

In electrolysis of water with dilute

H_2SO_4

, what is the ratio (by moles) of

H_2

O_2

produced?

Example 4

hard

10.0

A current runs for

2.00

hours through molten

Al_2O_3

. Calculate the mass of aluminum deposited (

Al = 27

g/mol).

Example 5

hard

A constant current deposits

1.50

g of

Ni

(

58.7

g/mol,

Ni^{2+}

) in

30.0

minutes. What is the current in amperes?

Example 6

hard

At what minimum voltage will electrolysis of water proceed under standard conditions (

E^\circ_{O_2/H_2O} = +1.23

E^\circ_{H^+/H_2} = 0.00

V)?

Example 7

hard

5.0

A current runs for

1930

s through aqueous

CuSO_4

. Find the volume of

O_2

(at STP,

22.4

L/mol) produced at the anode.

Example 8

challenge

A factory needs to produce

1000

kg of aluminum per day by the Hall-Heroult process. What constant current (in amperes) is required? (

Al = 27

g/mol,

F = 96{,}500

C/mol)

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy

What kind of energy source does an electrolytic cell require?

Example 2

easy

Is the reaction in an electrolytic cell spontaneous or nonspontaneous?

Example 3

easy

In an electrolytic cell, oxidation still occurs at which electrode?

Example 4

easy

Electrolytic cells convert electrical energy into what?

Example 5

easy

Reduction occurs at which electrode in an electrolytic cell?

Example 6

easy

Name one industrial process that uses an electrolytic cell.

Example 7

easy

Does an electrolytic cell work like a battery (power source) or the opposite?

Example 8

easy

In electrolysis of water, gases form at the electrodes. At the cathode (reduction), which gas forms?

Example 9

medium

During electrolysis of molten

NaCl

, write the cathode half-reaction.

Example 10

medium

During electrolysis of molten

NaCl

, write the anode half-reaction.

Example 11

medium

Why can a battery not be used to reverse its own spontaneous reaction without an external source?

Example 12

medium

How many moles of electrons are needed to deposit 1 mol of

Al

from

Al^{3+}

by electrolysis?

Example 13

medium

In an electrolytic cell, the power supply pushes electrons toward which electrode?

Example 14

medium

Compare the sign of

\Delta G

for a galvanic versus an electrolytic cell reaction.

Example 15

medium

Electrolysis of aqueous

CuSO_4

deposits copper at the cathode. Write that half-reaction.

Example 16

medium

In electrolysis of aqueous

CuSO_4

, write the anode half-reaction (water is oxidized).

Example 17

medium

How many moles of electrons are needed to deposit 2 mol of

Cu

from

Cu^{2+}

Example 18

challenge

A current of 5.0 A runs for 1930 s through molten

AlCl_3

. How many grams of Al deposit? (Al = 27 g/mol, F = 96500 C/mol)

Example 19

challenge

Electrolysis deposits 0.020 mol of a metal

M

from

M^{2+}

using 0.040 mol of electrons. Verify the charge and find moles of electrons for 0.10 mol of

M

Example 20

challenge

To electrolytically reverse a galvanic cell with

E^\circ_{cell}=+0.46

V, what is the minimum applied voltage, and what is the sign of

\Delta G

for the driven (reverse) reaction?

Example 21

easy

In an electrolytic cell, which electrode is connected to the positive terminal of the battery?

Example 22

easy

What is the SI unit of electric charge used in electrolysis calculations?

Example 23

easy

What does the value of Faraday's constant represent?

Example 24

easy

Does electroplating use a galvanic or an electrolytic cell?

Example 25

easy

What happens to the anode mass during electrorefining of copper, where the impure copper is the anode?

Example 26

medium

A current of

2.00

A flows for

30.0

minutes. How many coulombs of charge pass through the cell?

Example 27

medium

How many moles of electrons correspond to

96{,}500

C of charge?

Example 28

medium

In electrolysis of aqueous

NaCl

(brine), why is

Cl_2

produced at the anode rather than

O_2

Example 29

medium

During electrolysis of aqueous

NaCl

, what is the cathode product and why?

Example 30

medium

A current of

3.00

A passes for

1.00

hour through molten

MgCl_2

. How many grams of

Mg

deposit (

Mg = 24

g/mol)?

Example 31

medium

Electrolysis of

1.00

L of

1.0

CuSO_4

delivers

0.20

mol of electrons. By how much does

[Cu^{2+}]

decrease?

Example 32

medium

In an electrolytic cell, the cathode is labeled with what sign?

Example 33

medium

During electrolysis, do electrons flow through the external wire from anode to cathode or cathode to anode?

Example 34

medium

What is the role of an inert electrode (like platinum) in electrolysis?

Example 35

hard

Two electrolytic cells are connected in series: cell A contains

AgNO_3

and cell B contains

CuSO_4

. If

0.50

g of

Cu

(

63.5

g/mol) deposits in B, how much

Ag

(

108

g/mol) deposits in A?

Example 36

hard

Electrolysis of aqueous

Na_2SO_4

does not deposit Na metal. What products form at the cathode and anode, respectively?

Example 37

hard

In electroplating, a spoon is to be coated with silver from

AgNO_3

. Which electrode should the spoon be connected to?

Example 38

challenge

A galvanic cell using

Zn|Zn^{2+}||Cu^{2+}|Cu

has

E^\circ_{cell} = +1.10

V. To run this redox in reverse as an electrolytic cell, what is the minimum applied voltage, and what is the sign of

\Delta G^\circ

for the driven reverse reaction?

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Related Concepts

Electrochemical Cell

Background Knowledge

These ideas may be useful before you work through the harder examples.

electrochemical cell