Electrolysis (Igcse), Electrolysis Igcse Flashcards
Electrolysis
The breaking down of an ionic compound when molten or in an aqueous solution by the passage of electricity.
Electric current
Causes a chemical reaction that breaks down the ionic compound.
Electrolyte
The compound that conducts electricity when molten and breaks down during electrolysis.
Electrodes
Rods that carry electric current to and from the electrolyte.
Anode
Positive electrode.
Cathode
Negative electrode.
Positive ions
Form at the cathode.
Negative ions
Form at the anode.
Inert conductor
Unreactive conductor that won't interfere with the electrolysis.
Brine
Concentrated aqueous solution of sodium chloride, obtained from seams of rock salt underground.
Electrolysis of brine produces...
Chlorine, hydrogen, sodium hydroxide.
Brine is electrolysed in...
A diaphragm cell.
At the anode...
Ions lose electrons.
At the cathode...
Ions gain electrons.
Oxidation
Reaction with loss of electrons.
Reduction
Reaction with gain of electrons.
OILRIG
Oxidation is loss, Reduction is gain.
Anions
Negative ions.
Cations
Positive ions.
Half-equations
Ionic equations that only show what is happening at only one of the electrodes.
Define reduction?
Gain of electrons
Define oxidation?
Loss of electrons
What is an electrolyte?
Liquids that are good conductors of electricity
What is electrolysis?
The process of splitting up a chemical compound into its elements by the passage of an electric current.
Define a conductor?
A material that allows heat and electricity to pass through it.
Define an insulator?
A material that does not allow heat or electrons to move through it easily.
Define molten?
melted by heat
During electrolysis what do you understand by the term 'discharge'?
lose its charge, become neutral
inert substance is ........
unreactive
non-electrolytes are ......
Liquids that do not conduct electricity
What are electrodes?
A graphite (inert) or metal strip that conducts electricity.
The cathode is the .......
Negative electrode
The anode is the ........
Positive electrode
An anion is ..........
A negatively charged ion
A cation is ........
A positively charged ion
What is electroplating?
An electrolytic process in which metal ions are reduced and the metal atoms are deposited on a surface
Which cation (metal or hydrogen) gets discharged during electrolysis of an aqueous solution?
the least reactive
Which anion (OH- or halide) gets discharged during electrolysis of an aqueous solution?
usually the halide ion (unless very dilute)
What forms at the cathode?
either a metal or hydrogen
what forms at the anode
a non metal other than hydrogen
what is brine
Concentrated sodium chloride solution
Why do ionic compounds only conduct when molten or aqueous?
Ions are fixed when ionic compounds are solid, meaning they can't move so can't conduct electricity. When the compounds are molten or in aqueous solution, the ions (that are electrically charged) are able to move and carry charge.
To which electrodes do the lead and bromide ions go during the electrolysis of PbBr2
Lead is positively charged and moves to the negative electrode (cathode). Bromine is negatively charged and move to the positive electrode (anode).
Does oxidation occur at the anode or cathode?
Oxidation occurs at the anode. Oxidation is the loss of electrons.
Does reduction occur at the anode or cathode?
Reduction occurs at the cathode. Reduction is the gain of electrons.
Why is a mixture of aluminium oxide and cryolite used, rather than aluminium oxide alone?
Cryolite lowers the melting point and reduces some of the energy costs involved in extracting aluminium oxide.
Why during the extraction of aluminium from aluminium oxide, do the anodes need to be replaced during ?
Since the positive electrodes are made of carbon they get corroded by the oxygen forming carbon dioxide and so must be replaced every few weeks
Give 2 uses for chlorine
Kills harmful bacteria in swimming pools To sterelise the domestic water supplyTo manafacture PVC
Give 2 uses for sodium hydroxide
Used to make soap Manufacture bleach (with chlorine)