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Understand 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. The diagram below shows an electrolytic cell while electrolysis of sodium chloride (NaCl) is taking place:

 

Image of electrolysis

 

The principle is that the electric current separates the compound into its ions. Ions are atoms that have gained or lost one or more electrons in order to make the compound with the other element(s). The electrodes used for electrolysis are a positive one (anode), which attracts negative ions (anions), and a negative one (cathode), which attracts positive ions (cations). 

The electrolyte is the molten compound or the solution that is separated during electrolysis, and it must be able to conduct electricity.

 

Electrolysis of dilute sulfuric acid

Hydrogen is made at the cathode2H+ + 2e- Right facing arrow H2. The positive hydrogen ions migrate towards the negative cathode, gain one electron each and are discharged as hydrogen gas.

Oxygen is made at the anode: 4OH- - 4e-  Right pointing arrow 2H2O + O2. The negative hydroxyl ions migrate towards the positive anode, they lose one electron each and combine to form water and oxygen.

 

Purifying copper

Electrolysis is also used to purify metals, such as copper. Copper is extracted as an ore (compounds of copper with other elements) and is purified with this method. The anode is the impure copper;  it dissolves into the electrolyte, and pure copper coats the cathode. This is called electroplating.

 

Let's have a go at some questions now.

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

An electric current

A hammer

An acid

What is a compound separated into by electrolysis?

Atoms

Ions

Metals

What is the positive electrode called?

Anode

Cathode

What is the negative electrode called?

Anode

Cathode

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

Electromagnet

Electrolyte

Element

What do we call the negative ions that are attracted to the anode?

Onions

Anodions

Anions

What do we call the positive ions that are attracted to the cathode?

Cathions

Cations

Cathides

What is produced at the cathode during electrolysis of dilute sulfuric acid?

Sulfur dioxide

Hydrogen

Oxygen

What is produced at the anode during electrolysis of dilute sulfuric acid?

Hydrogen

Carbon dioxide

Oxygen

Which electrode is pure copper found at during its purification using electrolysis?

Positive electrode

Cathode

Anode

  • Question 1

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

CORRECT ANSWER
An electric current
EDDIE SAYS
The clue is in the word - 'electrolysis'. An electric current is used to separate substances into their compounds during electrolysis. It is needed to attract the ions in the substance you are trying to separate.
  • Question 2

What is a compound separated into by electrolysis?

CORRECT ANSWER
Ions
EDDIE SAYS
If you found this one difficult, you might find it helpful to have a go at the activity on ionic bonding. A compound is separated into ions through the process of electrolysis. Ions are atoms that have gained or lost one or more electrons in order to combine with the other element(s) to make the compound.
  • Question 3

What is the positive electrode called?

CORRECT ANSWER
Anode
EDDIE SAYS
The positive electrode is the anode and it attracts negative ions (anions). The other one is the cathode which will attract the positive ions (anions).
  • Question 4

What is the negative electrode called?

CORRECT ANSWER
Cathode
EDDIE SAYS
The negative electrode is the cathode. It attracts positive ions (cations). The positive electrode is the anode which attracts negative ions (anions).
  • Question 5

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.
  • Question 6

What do we call the negative ions that are attracted to the anode?

CORRECT ANSWER
Anions
EDDIE SAYS
Hopefully, you didn't fall into the trap of choosing one of the rather ridiculous-sounding incorrect options! The negative ions attracted to the anode are called anions. Positive ones would be cations.
  • Question 7

What do we call the positive ions that are attracted to the cathode?

CORRECT ANSWER
Cations
EDDIE SAYS
The positive ions attracted to the cathode are called cations. The negative ions that are attracted to the anode are called anions. It's important to get these two sorted out correctly.
  • Question 8

What is produced at the cathode during electrolysis of dilute sulfuric acid?

CORRECT ANSWER
Hydrogen
EDDIE SAYS
Now these questions are getting on to more complex stuff like word equations, but don't panic! The Introduction offers some good information to help you to choose the correct option. Hydrogen is produced at the cathode during electrolysis of dilute sulfuric acid:
2H+ + 2e- → H2.
  • Question 9

What is produced at the anode during electrolysis of dilute sulfuric acid?

CORRECT ANSWER
Oxygen
EDDIE SAYS
This complicated word equation and its explanation can be found in the Introduction - it might be worth a second look. Oxygen is produced at the anode during electrolysis of dilute sulfuric acid:
4OH- - 4e- → 2HO + O2.
  • Question 10

Which electrode is pure copper found at during its purification using electrolysis?

CORRECT ANSWER
Cathode
EDDIE SAYS
Pure copper coats the cathode. This is because it is a positive ion (because it is metal) and positive is attracted to negative - the cathode is the negative electrode. Did you get this final question? There's some tricky stuff in this topic, so make sure you learn the important bits. Make sure you know your positives from your negatives! Well done for completing another activity.
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