C2.7 Electrolysis

Question 1

What is electrolysis?

Answer 1

passing current through ionic substances that are molten or in solution, which breaks them down into elements

Question 2

In electrolysis, what is the electrolyte?

Answer 2

the substance that is broken down into elements

Question 3

Describe electroplating

Answer 3

uses electricity to coat the surface of one metal with another metal

negative electrode is the metal object you want to plate

positive electrode is pure metal you want to plate it with

electrolyte contains ions of the plating metal

Question 4

Why do people electroplate objects?

Answer 4

• Decoration- cheaper to plate another metal with silver than have solid silver
• Conduction- copper plating, copper used to plate electronic circuits

Question 5

What does OIL RIG stand for?

Answer 5

O xidation

I s

L osing

R eduction

I s

G ain

Question 6

At the negative electrode, positively charged ions…

Answer 6

gain electrons (reduction)

Question 7

At the positive electrode, negatively charged ions…

Answer 7

lose electrons (oxidation)

Question 8

Describe the electrolysis of sodium chloride solution

Answer 8

in the solution there are H+ Na+ OH- and Cl- ions

The more reactive the ion, the keener it is to stay an ion in the electrolyte.

Hydrogen is attracted to negative electrode (less reactive than sodium). 2 hydrogen ions gain 2 electrons (reduction) and become one hydrogen molecule.

2 chloride ions lose their electrons (oxidation) and become one chlorine molecule

sodium hydroxide is left in the solution

Question 9

What happens to the ions when an ionic substance is melted or dissolved in water?

Answer 9

the ions are free to move about within the liquid or solution

positively charged ions move to the negative electrode (cathode)

negatively charged ions move to the positive electrode (anode)

Question 10

What are the products of the electrolysis of sodium chloride solution and what can then be used for?

Answer 10

hydrogen

chlorine- production of bleach and plastics

sodium hydroxide solution- alkali, production of soap

Question 11

Describe the electrolysis of aluminium

Answer 11

Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite.

Aluminium forms at the negative electrode and oxygen at the positive electrode.

The positive electrode is made of carbon, which reacts with oxygen to produce carbon dioxide

Question 12

What is cryolite?

Answer 12

a less common ore of aluminium

Question 13

Why is cryolite used in the production of aluminium by electrolysis?

Answer 13

Aluminium oxide is dissolved in molten cryolite as cryolite brings the melting point of aluminium oxide down

so it is a cheaper and easier process

Question 14

In the production of aluminium by electrolysis, why are the positive electrodes made out of carbon and why can this be a problem?

Answer 14

As carbon is a good conductor of electricity

oxygen reacts with carbon to form carbon dioxide. This means that the positive electrode gradually gets worn away so needs to be replaced

Question 15

Describe how electrolysis is used to make pure copper from a lump of impure copper

Answer 15

impure copper is the positive electrode

pure copper is the negative electrode

electrolyte is any soluble copper salt in solution

copper forms positive ions and is attracted and reduced at the negative electrode

impurities collect at the bottom as they are not attracted to the electrodes