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Electrolysis

Worksheet Overview

QUESTION 1 of 10

An electric current can be used to separate compounds into their different elements, and also to create new products using a method called electrolysis. Electrolysis works for ionic compounds where the ions can move- that means they need to be molten or dissolved.

First example: electrolysis of molten compounds, like sodium chloride

The simplest types of electrolysis to understand are where we do electrolysis on a molten substance. For example, if we heat up sodium chloride enough, it melts. The liquid contains Na+ ions and Cl- ions.

Because of the battery, electrons move through the wires from the anode through the battery to the cathode. The anode electrode becomes positively charged, and the cathode electrode becomes negatively charged. The charges on the anode and cathode then attract the ions in the molten NaCl. The positively charged sodium cations are attracted to the negatively charged cathode, because opposite electrical charges attract. The negatively charged chloride anions are attracted to the positively charged anode for the same reason.

Once the ions reach the electrodes, they interact with electrons:

At the anode, the chloride anions lose their excess electrons, and are turned into chlorine atoms. Loss of electrons is called oxidation.

At the cathode, the sodium cations gain electrons, and are turned into sodium atoms. Gain of electrons is called reduction.

Second example: electrolysis of solutions, like copper sulfate in water

The copper sulfate example is more complicated, but it is a common experiment, so it's useful to know what happens in outline.

The setup is the same as before, but there are now four types of ion in the solution. The copper sulfate gives us Cu2+ and SO42-. The water breaks down into H+ and OH-. Like before, the positive cations are attracted to the cathode and the negative anions are attracted to the anode.

At the anode, the hydroxide anions lose their excess electrons, and the oxygen from the hydroxide becomes oxygen gas. This is oxidation.

At the cathode, the copper cations gain electrons, and are turned into copper atoms. Gain of electrons is called reduction.

Although a lot of the details of electrolysis get complicated- especially once there are more than two ions involved- the main idea is pretty easy. Melt or dissolve an ionic compound so the ions can move, then use charged electrodes to pull differently charged ions in different directions.

 

 

What is used to separate substances into their compounds during electrolysis?

An electric current

A hammer

An acid

Which of these phrases describe the positive electrode in electrolysis? Tick all the correct answers.

anode

cathode

attracts positive ions

attracts negative ions

attracts anions

attracts cations

What do we call the molten compound or solution that is separated?

Electromagnet

Electrolyte

Element

If we do electrolysis on molten lead bromide, what is the cation and what is the anion?

Electromagnet

Electrolyte

Element

Which of these phrases describe the negative electrode in electrolysis? Tick all the correct answers.

anode

cathode

attracts positive ions

attracts negative ions

attracts anions

attracts cations

If we do electrolysis on lead bromide, where does lead form? Tick all the right answers.

positive electrode

negative electrode

cathode

anode

If we do electrolysis on copper iodide, where does iodine form? Tick all the right answers.

positive electrode

negative electrode

cathode

anode

Which of these substances is able to conduct electricity in electrolysis?

solid NaCl

solid Al

NaCl dissolved in water

molten Al2O3

In electrolysis, what is oxidation?

Loss of electrons, taking place at the anode

Gain of electrons, taking place at the anode

Loss of electrons, taking place at the cathode

Gain of electrons, taking place at the cathode

In electrolysis, what is reduction?

Loss of electrons, taking place at the anode

Gain of electrons, taking place at the anode

Loss of electrons, taking place at the cathode

Gain of electrons, taking place at the cathode

  • Question 1

What is used to separate substances into their compounds during electrolysis?

CORRECT ANSWER
An electric current
EDDIE SAYS
An electric current is used to separate substances into their compounds during electrolysis. That's because oppositely charged ions are attracted to different electrodes.
  • Question 2

Which of these phrases describe the positive electrode in electrolysis? Tick all the correct answers.

CORRECT ANSWER
anode
attracts negative ions
attracts anions
EDDIE SAYS
The positive electrode is the anode and it attracts negative ions, called anions. The names match up, but the charges are opposite.
  • Question 3

What do we call the molten compound or solution that is separated?

CORRECT ANSWER
Electrolyte
EDDIE SAYS
The molten compound or solution that is separated is the electrolyte. This could be any product that you want to separate such as aluminium oxide or sodium chloride. It needs to be molten or dissolved so that the ions are free to move.
  • Question 4

If we do electrolysis on molten lead bromide, what is the cation and what is the anion?

CORRECT ANSWER
EDDIE SAYS
In ionic compounds, the metal is the cation (it loses electrons to be positively charged), and the non-metal is the anion. Notice the name of the anion as well- the atom is bromine, but the anion is bromide.
  • Question 5

Which of these phrases describe the negative electrode in electrolysis? Tick all the correct answers.

CORRECT ANSWER
cathode
attracts positive ions
attracts cations
EDDIE SAYS
The negative electrode is the cathode and it attracts positive ions, called cations. The names match up, but the charges are opposite.
  • Question 6

If we do electrolysis on lead bromide, where does lead form? Tick all the right answers.

CORRECT ANSWER
negative electrode
cathode
EDDIE SAYS
Lead ions are positively charged cations, so they are attracted to the negative electrode, which is the cathode.
  • Question 7

If we do electrolysis on copper iodide, where does iodine form? Tick all the right answers.

CORRECT ANSWER
positive electrode
anode
EDDIE SAYS
Iodide ions are negatively charged anions, so they are attracted to the positive electrode, which is the anode.
  • Question 8

Which of these substances is able to conduct electricity in electrolysis?

CORRECT ANSWER
NaCl dissolved in water
molten Al2O3
EDDIE SAYS
Sodium chloride dissolved in water can conduct electricity, because the ions can move. Molten aluminium oxide can conduct electricity for the same reason. Solid aluminium can conduct electricity, but there aren\'t cations and anions to separate. Solid sodium chloride has ions, but they can\'t move.
  • Question 9

In electrolysis, what is oxidation?

CORRECT ANSWER
Loss of electrons, taking place at the anode
EDDIE SAYS
Oxidation is the loss of electrons (some people remember this as OLIRIG: oxidation is loss, reduction is gain). In electrolysis this happens at the positively charged electrode, which is the anode.
  • Question 10

In electrolysis, what is reduction?

CORRECT ANSWER
Gain of electrons, taking place at the cathode
EDDIE SAYS
Reduction is the gain of electrons (some people remember this as OLIRIG: oxidation is loss, reduction is gain). In electrolysis this happens at the negatively charged electrode, which is the cathode.
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