Electrolysis Flashcards
How could the students separate the silver from the silver nitrate solution?
by filtration
The products at the electrodes are lead and bromine.
Why should the teacher do the demonstration in a fume cupboard?
toxic / poisonous fumes
Explain the difference between the processes in electrolysis and in a
chemical cell.
electrolysis uses electricity to produce a chemical reaction
(but) cells use a chemical reaction to produce electricity
Some of the copper produced did not stick to the negative electrode but fell
to the bottom of the beaker.
Suggest how the students could find the total mass of copper produced.
filter the mixture
wash and dry the copper / residue
weigh the copper collected
add to the increase in mass of the electrode
Copper nitrate solution is blue.
Suggest why the blue colour of the copper nitrate solution fades during the
electrolysis
copper ions are discharged (from the solution)
‘The electrolysis of a salt solution produces a metal at the negative electrode and
a gas at the positive electrode.’ What observation would be made at each electrode if the hypothesis is
correct?
(negative electrode) solid produced
(positive electrode) bubbles / fizzing / effervescence
Give two reasons why graphite is used for the electrodes.
(graphite) conducts (electricity)
(graphite) is inert (unreactive)
The purple crystal contained:
* colourless positive ions
* purple coloured negative ions.
The purple crystal dissolved in the electrolyte solution.
(d) What happens to the purple coloured ions?
the ions move towards the positive electrode
bc
the electrode attracts ions of the opposite charge
What is meant by an ‘alloy’?
a mixture of metals
Bauxite contains between 15% and 25% aluminium.
Aluminium oxide always contains 53% aluminium.
How does this show that bauxite is a mixture and not a compound?
bauxite contains a variable percentage of aluminium
Suggest two possible problems with storing the waste material in lakes of
mud.
leakage of toxic substances from mud to environment
* danger of dam bursting
* water pollution
* damage to habitats
* visual pollution
* (dam) blocks light
* reduces the value of houses
The formula of cryolite is Na3AlF6
Give the total number of atoms in the formula
10
What is the reason for adding cryolite to the aluminium oxide?
to lower the melting point of the mixture
When the molten aluminium oxide and cryolite mixture is electrolysed the
product at
the positive electrode is:
oxygen
oxygen reacts with the positive electrode because the positive electrode is made of:
carbon
Name the substance in the solution that provides the hydroxide ions.
water
Describe how the solid forms at the negative electrode. (copper chromate)
copper ions gain two electrons
(to) form copper (atoms)
Cu2+ + 2e- → Cu
Name the product at each electrode when potassium iodide solution is
electrolysed.
Negative electrode:
positive elecctrode:
hydrogen
iodine
Aluminium is produced by electrolysing a molten mixture of aluminium oxide and
cryolite.
Explain why a mixture is used as the electrolyte instead of using only
aluminium oxide.
mixture has a lower melting point
(so) less energy needed
What happens at the negative electrode during the production of
aluminium?
aluminium ions gain electrons
Complete the balanced half-equation for the process at the positive
electrode.
2 O2- → O2 + 4 e
Explain why the positive electrode must be continually replaced.
the electrode reacts with oxygen
the electrode is carbon / graphite
(so) carbon dioxide is produced
Sodium metal and chlorine gas are produced by the electrolysis of molten
sodium chloride.
Explain why sodium chloride solution cannot be used as the electrolyte to
produce sodium metal.
hydrogen (gas) would be produced (instead of sodium)
(because) sodium is more reactive than hydrogen
The teacher demonstrates the electrolysis of:
* molten zinc chloride
* potassium bromide solution.
Product at cathode
(negative electrode)
Product at anode
(positive electrode) is what
zinc , hydrogen at cathode
chlorine , bromine at anode
