Chemistry - Chem 4: Electrolysis

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  • Created by: shcoool
  • Created on: 25-05-15 15:30
What is electrolysis?
It is a process in which electricity is passed through a liquid substance and the liquid is decomposed.
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What is an electrolyte?
The liquid which conducts electricity and is decomposed. Usually molten ionic compounds or aqueous solutions of ionic compounds.
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What are electrodes?
They are the rods which dip into the electrolyte. Often made of carbon or platinum (have to be made of
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What is the positive and negative electrodes called?
positive - anode, negative - cathode
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What do oxidation and reduction involve?
Oxidation is loss of electrons and reduction is gain of electrons (OILe RIGe)
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What are ionic compounds made of?
positive ions and negative ions
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Why can solid ionic compounds not conduct electricity?
The ions are unable to move so they cannot conduct electricity
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What happens when ectricity flows through an electrolyte?
The current is carried by moving ions because when an ionic compound is molten or dissolves in water, the ions are free to move.
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What is the movement of ions?
An electric current
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What is the half equation of the electrolysis of sodium chloride?
NaCl (l) > Na+ (l) + Cl- (l)
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What happens at the cathode and anode?
At the cathode, metal ions gain electrons and so are reduced. At the anode, non-metal metal ions lose electrons and so are oxidised.
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What is the half equation at the cathode?
Na+ + e- > Na
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What happens to the sodium ions?
They become sodium atoms.
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What is the hal equation at the anode?
(2)Cl- > Cl2 + (2)e-
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What happens to the chloride ions?
They are oxidised to make chlorine molecules.
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In molten electrolytes, what happens?
At the cathode, metals are produced. At the anode, non-metals are produced. At the cathode, metal ions are reduced to atoms. At the anode, non-metal ions are oxidised to make
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What is made at the cathode in aqueous electrolytes?
Metals more reactive than hydrogen are not produced at the cathode. Instead hydrogen gas is produced from the hydrogen ions in the water. Metals less reactive than hydrogen are produced at the cathode.
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What is made at the anode in aqueous electrolytes?
Negative ions are not discharged at the anode. Instead oxygen gas is produced from the hydroxide ions in water. Halide ions (from group 7) are discharged at the anode, making a halogen. The hydrogen ions from the water make hydrogen at the cathode.
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What is made when water decomposes?
hydrogen ions and hydroxide ions.
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What are the half equations of hydrogen ions and hydroxide ions?
cathode - hydrogen (2)H+ + (2)e- > H2 anode - water and oxygen (4)OH- > (2)H20 + )2 + (4)e-
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What happens during the purification of copper?
Impure copper is made at the anode; pure copper is made at the cathode. The electrolyte is copper sulfate solution. Copper dissovles at the anode ans pure copper is deposited at the cathode. The anode slime may contain gold and silver.
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What happens during the extraction of aluminium?
Extracted from bauxite, which is aluminium oxide with some red iron oxide and silicon dioxide. It's purified and dissolved in molten cryolite at 1000degreescelsius. Aluminium collects at the cathode and oxygen is made at the anode.
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What is also produced during the electrolysis of bauxite?
The naode is made of carbon so reacts with the oxygen to make carbon dioxide.
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Name one use of electrolysis
Electroplating
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What happens during electroplating od nickel on steel?
The steel object is made at the cathode and pure nickel is made at the anode. The electrolyte is nickel sulphate. Nickel is deposited on the steel cathode.
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Why is electoplating carried out?
To make sure the underlying metal is less likely to corrode or to make the object more decorative.
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What is brine?
It is a saturated solution of sodium chloride.
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What happens when brine is electrolysed in a membrane cell?
There are sodium ions, chloride ions, hydrogen ions and hydroxide ions. Hydrogen gas is made at the cathode. Water and oxygen is made at the anode, leaving sodium ions and hydroxide ions in solution.
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Why is the membrane important?
It only allows positive ions to pass through which prevents the chlorine gas from reacting with the sodium hydroxide.
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What can the products be used for?
Hydrogen - margarine or ammonia; chlorine - disenfecting swimming pools or PVC; sodium hydroxide - oven cleaner or soap
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Card 2

Front

What is an electrolyte?

Back

The liquid which conducts electricity and is decomposed. Usually molten ionic compounds or aqueous solutions of ionic compounds.

Card 3

Front

What are electrodes?

Back

Preview of the front of card 3

Card 4

Front

What is the positive and negative electrodes called?

Back

Preview of the front of card 4

Card 5

Front

What do oxidation and reduction involve?

Back

Preview of the front of card 5
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