Chemistry Unit 2- Electrolysis

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  • Created by: Bella B
  • Created on: 09-01-16 21:14
What is ELECTROLYSIS?
ELECTROLYSIS is the breaking down of a substance using ELECTRICITY.
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When can IONIC COMPOUNDS only be electrolysed?
When they are molten or in solution- their IONS are free to move!
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What happens in Electrolysis?
POSITIVE ions move to the NEGATIVE electrode, while NEGATIVE ions move to the POSITIVE electrode.
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NEGATIVE ions are ???
NEGATIVE ions are OXIDISED!
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POSITIVE ions are ???
POSITIVE ions are REDUCED!
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What happens when Electrolysis takes place in water?
The LESS reactive metal- between H2 and the metal- is usually PRODUCED at the NEGATIVE ELECTRODE.
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What happens at the positive electrode in water?
At the positive electrode= O2 gas given off from discharged hydroxide ions!
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What are HALF EQUATIONS?
They represent what happens at each electrode.
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What's the Half Equation at the NEGATIVE electrode?
Positive ions gain electrons at the negative electrode, so are reduced. In aluminium extraction: Al3+ + 3e- → Al. In copper purification: Cu2+ + 2e- → Cu. Electrolysis of sodium chloride solution: 2H+ + 2e- → H2
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What's the Half Equation at the POSITIVE electrode?
Negative ions or neutral atoms lose electrons at the positive electrode and are oxidised. In aluminium extraction: 2O2- → O2 + 4e-. In copper purification: Cu → Cu2++ 2e-.
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What is the most abundant metal on the Earth?
ALUMINIUM! However, it's expensive, largely because of the amount of electricity used up in the extraction process.
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What happens in the extraction of ALUMINIUM?
1) Aluminium Oxide is electrolysed in the manufacture of aluminium metal. 2) The Aluminium Oxide is mixed with molten cryolite. 3) Aluminium forms at the cathode and oxygen at the anode. The carbon electrodes are replaced regularly.
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Why is CRYOLITE mixed with Aluminium Oxide?
To lower the melting point of Aluminium Oxide, as it would be expensive to melt it at its normal melting point!
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Why are the carbon electrodes replaced regularly?
They gradually burn away due to the production of CO2!
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What products are made in the electrolysis of BRINE?
1) CHLORINE GAS. 2) HYDROGEN GAS. 3) SODIUM HYDROXIDE SOLUTION.
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What is Chlorine Gas used for?
To make BLEACH- it kills bacteria and to make PLASTICS.
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What is Hydrogen Gas used for?
To make MARGARINE- by hydrogenation.
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What is Sodium Hydroxide Solution used for?
To make BLEACH, PAPER and SOAP!
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Why is ELECTROPLATING used?
Electroplating objects is used to improve their appearance, protect their surface and to use smaller amounts of precious metals!
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Where is the object that is to be electroplated placed?
AT the NEGATIVE electrode in an electrolysis cell!
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Where is the plating metal placed?
At the POSITIVE electrode.
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What is an ELECTROLYTE?
A liquid which conducts electricity.
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Why can COVALENT COMPOUNDS not act as an electrolyte?
For electrolysis to work, the compound must contain ions. Covalent compounds cannot act as electrolytes because they contain neutral atoms.
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What is ELECTRICITY?
Electricity is the flow of electrons or ions.
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How can you test for Electriity?
To test for conductivity, include a sample of the substance in a circuit that contains a source of direct current (eg. a cell) and a bulb or an ammeter. If a current flows through the substance when it is molten or dissolved, it is an electrolyte.
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What makes an electrolyte?
To be an electrolyte, a substance must be able to conduct electricity.
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Why is it easy to predict the products of electrolysis- molten electrolytes?
They split into the products-the metal is formed at the negative electrode (that is where the positive metal ions are attracted) and the non-metal element is formed at the positive electrode (that is where the negative non-metal ions are attracted)
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Where does Oxidation occur?
Oxidation happens at the anode- because electrons are lost.
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Where does Reduction occur?
Reduction happens at the cathode- because electrons are gained.
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What does OILRIG mean?
Oxidation Is Loss of electrons, Reduction Is Gain of electrons.
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Other cards in this set

Card 2

Front

When can IONIC COMPOUNDS only be electrolysed?

Back

When they are molten or in solution- their IONS are free to move!

Card 3

Front

What happens in Electrolysis?

Back

Preview of the front of card 3

Card 4

Front

NEGATIVE ions are ???

Back

Preview of the front of card 4

Card 5

Front

POSITIVE ions are ???

Back

Preview of the front of card 5
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