Flashcards in C3.3 Electrolytic processes Deck (82)
How do you break the bonds in an ionic solid?
By melting it or dissolving it in water
What are electrolytes?
Ionic substances that conduct electricity when molten or in aqueous solution
Why do ionic substances have to be molten or in aqueous solution in order to conduct electricity?
Because then the ions are able to move freely
What is electrolysis?
The chemical decomposition of a compound produced by passing an electric current through a liquid or solution containing ions
What electrical supply does electrolysis use?
DC (direct current)
What things are necessary to carry out electrolysis?
-a DC electricity supply
What forces cause ions to move towards electrodes with opposite charges during electrolysis?
Electrostatic forces of attraction
What charge does a cathode have?
What charge does an anode have?
What charge does a cation have?
What charge does an anion have?
During the electrolysis of copper chromate solution what colour solution does the chromate form?
During the electrolysis of copper chromate solution what colour solution do the copper ions form?
What are electrodes made out of?
Metal or carbon
What happens to ions at the cathode?
Electrons from the negative cathode are transferred to the positive ions
What happens to ions at the anode?
The negative ions lose electrons to the positively charged anode
What is reduction?
When positive ions gain electrons
What is oxidation?
The loss of electrons by a negative ion
Why do chemical changes occur at the electrodes?
Because the transfer of electrons that happens there changes ions into atoms or molecules
During the electrolysis of sodium chloride, what ions are attracted to the cathode?
In the electrolysis of sodium chloride, what ions are attracted to the anode?
What is produced from the electrolysis of NaCl?
Sodium metal and chlorine gas
What are the uses of sodium?
In street lamps and as a coolant in nuclear reactions
How is sodium used in street lamps?
Sodium vapour gives out a bright yellow light when an electric current is passed through it
How is sodium used as a coolant in nuclear reactions?
Liquid sodium metal has a high thermal conductivity and transfers heat very efficiently from the core of the reactor to water, which then turns into steam and drives the generators
What does a half-equation for electrolysis show?
The change at just one of the electrodes
Why is hydrogen a clean fuel?
-it doesn't produce any of the pollutants that fossil fuels produce
-it doesn't produce carbon dioxide
What does it mean when a material is inert?
It won't react
Why does an electrode need to be made from an inert material?
So that it doesn't react with the electrolyte or the products during electrolysis
How can you measure the rate of reaction of gases during electrolysis?
Test tubes can collect the gases from the electrode, and the amount of time it takes for them to fill up and can show the rate of reaction
What does Hoffman's voltameter do?
Collect gases given off during electrolysis so that the volume can be read from the vertical tubes
What happens to the ions in a molten salt when it is electrolysed?
They become discharged as atoms or molecules at the electrodes
Why is an ion converted back to an element when it is discharged?
The loss or gain of electrons means that the number of electrons is back to being the same as the number of protons like in the original element
During the electrolysis of water, where is hydrogen produced?
At the cathode
What needs to be done to a salt before it is electrolysed?
It needs to dissociate into ions
What happens to the ionic bonds in a salt when it dissociates?
During the electrolysis of lead bromide, what is produced at the anode?
What form is the bromine produced from the electrolysis lead bromide in?
What does the bromine produce from the electrolysis of lead bromide look like?
A brown vapour
What form is the lead metal produced from the electrolysis of lead bromide in?
What is produced at the cathode during the electrolysis of lead bromide?
Why are hydroxide ions discharged at the anode instead of sulphate during the electrolysis of copper sulphate?
Hydroxide ions lose electrons more readily than sulphate ions
What is produced at the cathode during the electrolysis of sodium sulphate?
What is produced at the anode during the electrolysis of sodium sulphate?
Water and oxygen
What does it mean when a material is corrosive?
It corrodes, wears away or destroys things
What ions does salt water contain?
Sodium, chloride, hydrogen and hydroxide ions
What is produced at the anode and cathode from the electrolysis of salt water?
Chlorine and hydrogen gas
What happens to the ions left over from the electrolysis of salt water?
They form a solution of sodium hydroxide
Why is platinum wire used for flame tests?
It is inert
What can affect what happens during electrolysis?
-type of electrode used
-concentration of the solution
-distance between the electrodes
Why does increasing current increase the amount of product produced during electrolysis?
It increases the amount of electrons available at the electrodes for oxidation and reduction
Why must copper used for the production of wires be very pure?
Impurities increase resistance so the wire can get hot which can be dangerous
What process is used to extract copper from its ore?
What is smelting?
The extraction of ores by heating them with carbon
How is copper purified on an industrial scale after its extraction by smelting?
What does it mean when a product is impure?
It contains a mixture of other elements and compounds
What does it mean when a product is refined?
It's purity is increased
What are the electrodes used during the electrolysis of copper ore made from?
-the anode is the impure copper
-the cathode is a thin sheet of pure copper
What electrolyte is used in the electrolysis of copper ore?
Copper sulphate solution
How many electrons do copper atoms in the anode lose during the electrolysis of copper ore?
What are insoluble impurities from the anode during the electrolysis of copper ore called?
Why is anode sludge from the electrolysis of copper ore collected?
It could contain valuable metallic elements
What happens to dissolved copper ions from the anode during the electrolysis of copper ore?
They migrate towards the cathode where they are deposited as pure copper
Why does the cathode increase in mass as the anode decreases in mass during the electrolysis of copper ore?
Because for every copper atom that leaves the anode, one is deposited at the cathode
What happens when you electroplate something?
A thin layer of metal is deposited on the surface of another
What process is used to electroplate objects?
What electrode is the object to be plated when you're electroplating something?
What electrode is made of pure metal when you're electroplating something?
What ions must the electrolyte contain when you're electroplating something?
Ions from the plating metal (the anode)
What electrode does reduction occur at?
What electrode does oxidation occur at?
How do you increase the thickness of the layer of metal when electroplating?
-increasing the current
-carrying out electrolysis for longer
Why would an object be electroplated?
-to give an attractive appearance
-it's cheaper than making the object out of pure metal
-to improve resistance to corrosion
How does electroplating a metal improve its resistance to corrosion?
It prevents the plated metal from making contact with air
What is Galvanised steel?
Steel coated with zinc
What is rusting?
The corrosion of iron
Why does zinc protect iron in galvanised steel even when the coating is scratched?
Zinc is more reactive
What are the uses of electroplating with silver?
What are the uses of electroplating with gold?
What are the uses of electroplating with chromium?
What are the uses of electroplating with tin?
Steel food cans