Half Equations and terminology Flashcards
Copper (II) chloride solution electrolysis - anode reaction?
2Cl– (aq) → Cl2 (g) + 2e–
This is oxidation
Copper (II) chloride solution electrolysis - cathode reaction?
Cu2+ (aq) + 2e– → Cu (s)
This is reduction
Sodium chloride solution electrolysis - anode reaction?
2Cl– → Cl2 (g) + 2e–
This is oxidation
Sodium chloride solution electrolysis - cathode reaction?
2H+ (aq) + 2e– → H2 (g)
This is reduction
Sodium sulfate solution electrolysis - anode reaction?
O2- (aq) → O2 (g) + 2e–
This is oxidation
Sodium sulfate solution electrolysis - cathode reaction?
2H+ (aq) + 2e– → H2 (g)
This is reduction
Water acidified with sulphuric acid electrolysis - anode reaction?
2O2- (aq) → O2 (g) + 4e–
This is oxidation
Water acidified with sulphuric acid electrolysis - cathode reaction?
2H+ (aq) + 2e– → H2 (g)
This is reduction
Molten lead bromide electrolysis - anode reaction?
2Br– (l) → Br2 (g) + 2e–
This is oxidation
Molten lead bromide electrolysis - cathode reaction?
Pb2+ (l) + 2e– → Pb (l)
This is reduction
Copper (II) chloride solution electrolysis - what is formed at the anode?
Chlorine gas
Copper (II) chloride solution electrolysis - what is formed at the cathode?
Copper metal (deposited on the cathode) It is a brown / pink colour
Sodium chloride solution electrolysis - what is formed at the anode?
Chlorine gas
Sodium chloride solution electrolysis - what is formed at the cathode?
Hydrogen gas
Sodium sulfate solution electrolysis - what is formed at the anode?
Oxygen gas
Sodium sulfate solution electrolysis - what is formed at the cathode?
Hydrogen gas
Water acidified with sulphuric acid electrolysis - what is formed at the anode?
Oxygen gas
Water acidified with sulphuric acid electrolysis - what is formed at the cathode?
Hydrogen gas
Molten lead bromide electrolysis - what is formed at the anode?
Bubbles of bromine gas
Molten lead bromide electrolysis - what is formed at the cathode?
Lead metal
What does PANIC stand for?
Positive Anode Negative Is Cathode
What does OILRIG stand for?
Oxidation is a Loss of Electrons Reduction Is a Gain of Electrons
What is the name of the liquid in an electrolysis cell?
The electrolyte
What are the anode and cathode called together?
What are they usually made of?
The electrodes
They are usually made of carbon / graphite, but are made of copper when purifying copper (electrolysis of copper sulfate solution).
Is the cathode positive or negative?
Negative
Is the anode positive or negative?
Positive
Which Ionic compounds will conduct electricity?
Only ionic compounds that are molten (heated to melt) or dissolved in solution will conduct electricity.
This means that ions can move and transfer the current.
Will any covalent compounds conduct electricity?
Only graphite, since it has free electrons
How can we make lead molten?
By heating it to melt the lead
How do we know if hydrogen or a metal forms at the negative cathode?
Hydrogen gas is only produced at the cathode if the metal is more reactive than hydrogen (e.g. sodium with sodium sulphate electrolysis).
Copper is less reactive than hydrogen, so is produced at the anode (e.g. with copper (II) chloride electrolysis).
What is the test for carbon dioxide gas?
Turns limewater milky
What is the test for oxygen gas?
Relights a glowing splint
What is the test for hydrogen gas?
Squeaky pop test
What is the test for chlorine gas?
Red litmus turns blue and is then bleached white
Which ions are involved in the electrolysis of copper (II) chloride solution?
Positive = Cu2+ and H+ Negative = Cl- and OH-
Which ions are involved in the electrolysis of sodium chloride solution?
Positive = Na+ and H+ Negative = Cl- and OH-
Which ions are involved in the electrolysis of sodium sulfate solution?
Positive = Na+ and H+ Negative = SO4 2- and OH-
Which ions are involved in the electrolysis of water acidified with sulphuric acid?
Positive = H+ Negative = SO4 2- and OH-
Which ions are involved in the electrolysis of molten lead bromide?
Positive = Pb2+ Negative = Br-
What does inert mean (when talking about the electrodes)?
Unreactive
What does REDOX stand for?
RED - uction
and
OX - idation
Which metal is usually extracted from its ores using electrolysis?
Aluminium
Why is aluminium extracted from its ores using electrolysis?
Because aluminium is too reactive to extract by using carbon to displace it from its ore
What is aluminium ore (bauxite) mixed with to reduce the cost of its electrolysis
It is mixed with molten Cryolite.
Give two reasons why cryolite is used in the electrolysis of aluminium oxide.
The mixture of cryolite and aluminium oxide has a lower melting point than pure aluminium oxide.
This means a lower amount of energy is required to establish effective conditions for electrolysis and thus makes it more cost effective.
What is the name of aluminium ore?
bauxite
Where do positively charged cations migrate during electrolysis?
They move towards the oppositely / negatively charged cathode
Where do negatively charged anions migrate during electrolysis?
They move towards the oppositely / positively charged anode
What are electrolytes?
Electrolytes are ionic compounds in the molten state or dissolved in water
Define electrolysis
A process in which electrical energy, from a direct current supply, decomposes electrolytes
What are the electrodes made of during the purification of copper in the electrolysis of copper sulfate solution?
The electrodes are made of copper
EXAM QUESTION:
Zinc can be extracted from its ore by electrolysis or by heating the ore with carbon. Give a reason for the actual method that is used. (1 mark)
Heating with carbon is used since it is cheaper than using electrolysis.
EXAM QUESTION:
Identify the products formed at the anode and cathode when molten potassium iodide is electrolysed. (2 marks)
Iodine at the anode
Potassium at the cathode
EXAM QUESTION:
Copper is purified by the electrolysis of copper sulfate solution using an impure copper anode and a pure copper cathode.
Write the half-equation for the formation of a copper atom from a copper ion. (2 marks)
Cu2+ +2e- → Cu
EXAM QUESTION:
When a solution of sodium sulfate, Na2SO4, is electrolysed, the products formed at the electrodes are hydrogen and oxygen.
Explain the formation of the products at the electrodes.
(4 marks)
Hydrogen (H+) and sodium (Na+) ions attracted to the cathode
Hydroxide (OH−) ions and sulfate (SO42−) ions attracted to the anode
Since the ions are attracted to the oppositely charged
electrode
2H+ (aq) + 2e– → H2 (g)
O2- (aq) → O2 (g) + 2e–
EXAM QUESTION:
Which material is most suitable to make the electrodes for the electrolysis of a dilute acid?
A) zinc
B) sulfur
C) iron
D) graphite
(1 mark)
D) Graphite
EXAM QUESTION:
State what is meant by the term electrolyte (2 marks)
A substance that conducts electricity (1)
When molten or in aqueous solution (1)
EXAM QUESTION:
Copper sulfate solution was electrolysed for five minutes using copper electrodes.
Here are the results:
anode mass BEFORE electrolysis = 1.16g
anode mass AFTER electrolysis = 0.85g
cathode mass before electrolysis = 1.28g
cathode mass after electrolysis = 1.57g
Calculate the mass of copper deposited.
Copper is deposited on the cathode
Mass deposited = 1.57 – 1.28
= 0.29g
Which two ions does water dissociate into?
OH - and H+ ions
What do bubbles mean in electrolysis?
A gas is being produced
Define reduction
Reduction is a gain of electrons
Reduction is also a loss of oxygen
Define oxidation
Oxidation is a loss of electrons
Oxidation is also a gain of oxygen
