Chemistry - Electroylsis

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  • Created by: becky.65
  • Created on: 17-12-15 09:48
What is electrolysis?
The process that uses electricity to break down ionic compounds into elements
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Why can ionic compounds only be electrolysed when they are molten or in solution?
Because then their ions are free to move and carry their charge to the elecrodes
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What is the substance that is broken down called?
The electrolyte
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Which electrode are positively charged ions attracted to?
The cathode (negative electrode)
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What is formed at the cathode?
Metals or hydrogen
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Which electrode are negatively charged ions attracted to?
The anode (positive electrode)
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What is formed at the anode?
Non-metallic elements
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When positively charged ions reach the cathode, what happens to their charge?
They gain electrons to become neutral atoms
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What is gaining electrons called?
Reduction
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What happens to the charge of negative ions at the anode?
They lose electrons to become neutral atoms
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What is the loss of electrons called?
Oxidation
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Why might hydrogen be produced at the cathode?
This happens if the other positive ions in the solution are those of a metal more reactive than hydrogen
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At the anode, what gas is usually produced?
Oxygen
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Why might a halogen be produced at the anode?
If the solution contains a reasonably high concentration of a halide ion
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What is aluminium's ore called?
Bauxite
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What does bauxite contain?
Aluminium oxide
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What must first be done to bauxite so it can be electrolysed?
It must be purified then melted
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What temperature does aluminium oxide melt at?
Over 2000 degrees centigrade
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What can we do to lower aluminium oxide's melting point?
Mix it with another ionic compound called cryolite, so that the mixture melts at 850 degrees centigrade
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What happens at the cathode when electrolysing aluminium oxide?
Aluminium ions are reduced to aluminium atoms by gaining electrons
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What happens at the anode when electrolysing aluminium oxide?
Oxide ions are oxidised to oxygen atoms by losing electrons and the oxygen atoms form oxygen molecules
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What electrodes are used for electrolysing aluminium oxide?
Carbon electrodes
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Why must carbon electrodes be replaced regularly?
The oxygen reacts with carbon cathodes to produce carbon dioxide gas and this means they gradually burn away
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What does brine contain?
Sodium ions, chloride ions, hydrogen ions and hydroxide ions
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When we electrolyse brine, what is produced at the cathode?
Hydrogen from the hydrogen ions
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When we electrolyse brine, what is produced at the anode?
Chlorine from the chloride ions
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What solution is left after electrolysing brine?
An alkaline solution of sodium ions and hydroxide ions
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What are some of the uses of sodium hydroxide?
Making soap, paper, bleach, neutralising acids and controlling pH
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What are some of the uses of chlorine?
Kill bacteria, make bleach, disinfectants and plastics
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What is hydrogen used to make?
Margarine and hydrochloric acid
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What is electroplating?
It uses electrolysis to put a thin coating of metal onto an object
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What metals are often used for electroplating?
Gold, silver and chromium plating
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Why do we electroplate objects?
Make the object look more attractive; protect a metal from corroding; increase the hardness of a surface; reduce costs
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For electroplating, the object to be plated is used as which electode?
As the cathode
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For electroplating, the anode is made from what?
The plating metal
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For electroplating, the electrolyte is a solution containing what?
Ions of the plating metal
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At the anode, what happens to the atoms of the plating metal?
They lose electrons to form metal ions which go into the solution
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At the cathode, what happens to the object to be plated?
Metal ions from the solution gain electrons to form metal atoms which are deposited on the object to be plated
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Other cards in this set

Card 2

Front

Why can ionic compounds only be electrolysed when they are molten or in solution?

Back

Because then their ions are free to move and carry their charge to the elecrodes

Card 3

Front

What is the substance that is broken down called?

Back

Preview of the front of card 3

Card 4

Front

Which electrode are positively charged ions attracted to?

Back

Preview of the front of card 4

Card 5

Front

What is formed at the cathode?

Back

Preview of the front of card 5
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