5 Electrolysis Flashcards
How can you test and show that a substance is an electrolyte?
Use a circuit with a cell, lamp, wires and two graphite electrodes.
Place the two electrodes into the solution.
If the bulb lights then the solution is an electrolyte.
State why the electrodes used in electrolysis are usually made from an inert material.
So that they do not take part in the reactions that occur during electrolysis.
During electrolysis, anions move towards the….
ANODE
or postively charged electrode.
During electrolysis, cations move towards the….
CATHODE
or negatively charge electrode.
What are the products of electrolysis of magnesium chloride solution?
CATHODE - No Copper, silver, gold - therefore hydrogen forms
ANODE- Halide present! Chlorine forms
What are the products of electrolysis of a copper sulphate solution?
CATHODE - Copper, silver, gold present - therefore copper forms
ANODE- No halide present- oxygen forms
What are the products of the electrolysis of a sodium chloride solution?
CATHODE - No copper, silver, gold present - therefore hydrogen forms
ANODE- halide present- chlorine forms
What are the products of electrolysis of potassium sulphate solution?
CATHODE - No copper, silver, gold present - therefore hydrogen forms
ANODE- No halide present- therefore oxygen forms
Describe the movement of ions in an electrolytic cell.
Cations/positive ions move towards the cathode/negative electrode
Anions/negative ions move towards the anode/postive electrode
In the electrolysis of molten lead iodide, iodine gas forms at the anode.
The I- ion is attracted to the anode. iodide ion is oxidised/ loses an electron
2I- –> I2 + 2e-
Predict the reduction processes that occurs at the cathode.
CATHODE- attracts the cation - lead ion to form lead
Pb2+ + 2e- –> Pb
Lead ion is reduced- gains two electrons
In the electrolysis of molten sodium bromide, sodium metal forms at the cathode.
The Na+ ion is attracted to the cathode. Sodium ion is reduced/ gains an electron
Na+ + e- –> Na0
Predict the oxidation processes that occurs at the anode.
ANODE- attracts the anion - bromide ion to form bromine gas
2Br- –> Br2 + 2e-
Bromide ion is oxidised- loses electrons
Electrolysis was carried out on an aqueous solution of X
Product at CATHODE- hydrogen gas
Product at ANODE- oxygen gas
Suggest the identity of compound X
Any soluble salt which is not a copper, silver or gold salt AND not a halide salt.
Such as sodium sulfate OR potassium nitrate OR ammonium sulphate
Define electrolysis
The breaking down of a substance using electricity.
An electric current is passes through an electrolyte, causing it to decompose.
How do you know if a substance is reduced during electrolysis
OIL RIG
Reduction is gain of electrons.
Therefore, a cation is reduced when it gains electrons
How do you know if a substance is oxidised during electrolysis
Oxidation is loss of electrons.
Therefore, an anion is oxidised when it loses electrons
Which of the following compounds can be used as an electrolyte?
A - solid ionic compound
B- solid simple covalent compoound
C- soluble ionic compound in water
D- molten ionic compound
C and D only
both have ions which can move freely and carry charge
Half reactions show how electrons are transferred during reactions. They are really useful for showing what happens at each electrode during electrolysis.
Write the half reaction for O2- at the ANODE
2O2- –> O2 + 4e-
Half reactions show how electrons are transferred during reactions. They are really useful for showing what happens at each electrode during electrolysis.
Write the half reaction for Cl- at the ANODE
2Cl- –> Cl2 + 2e-
Half reactions show how electrons are transferred during reactions. They are really useful for showing what happens at each electrode during electrolysis.
Write the half reaction for Br- at the ANODE
2Br- –> Br2 + 2e-
Half reactions show how electrons are transferred during reactions. They are really useful for showing what happens at each electrode during electrolysis.
Write the half reaction for H+ at the CATHODE
2H+ + 2e- –> H2
Half reactions show how electrons are transferred during reactions. They are really useful for showing what happens at each electrode during electrolysis.
Write the half reaction for Cu2+ at the CATHODE
Cu2+ + 2e- –> Cu0
Half reactions show how electrons are transferred during reactions. They are really useful for showing what happens at each electrode during electrolysis.
Write the half reaction for Pb2+ at the CATHODE
Pb2+ + 2e- –> Pb0
Half reactions show how electrons are transferred during reactions. They are really useful for showing what happens at each electrode during electrolysis.
Write the half reaction for Na+ at the CATHODE
Na+ + e- –> Na0
Why is it more difficult to predict what products you get when you electrolyse SOLUTION substances?
SOLUTION substances have two possible CATIONS and two possible ANION to choose from.
NOTE: Water provides two other ions (H+ and OH-)
CATHODE- if the electrolyte contains copper, silver or gold, it forms, if not hydrogen gas forms
ANODE- if the the electrolyte contains a halide- halogen forms, if not oxygen forms.
Why is it easy to predict what products you get when you electrolyse MOLTEN substances?
MOLTEN substances only have one CATION and one ANION to choose from, there are no other possible products.
Which of the following are reduction reactions?
A 2H+ + 2e- –> H2
B 2Cl- –> Cl2 + 2e-
C 2O2- –> O2 + 4e-
D Pb2+ + 2e- –> Pb0
OIL RIG
Reduction is gain of electrons
Both A and D as both the ions gain electrons
Use the rules to decide what forms at both the CATHODE and ANODE in each example
CATHODE- Is there copper, silver or gold? if yes, it forms, if not hydrogen forms
ANODE - Is there a halide? if yes the halogen forms- if not oxygen forms
1st Row - hydrogen and oxygen
2nd Row - silver and bromine
3rd Row- hydrogen and oxygen
In the electrolysis of water, a small amount of sulfuric acid is added to the water to make the water more conductive.
hydrogen forms at the cathode
oxygen forms at the anode
Why is double the volume of hydrogen formed?
The formula of water is H2O
Therefore there is double the number of moles of hydrogen ions than oxygen ions forming double the volume of hydrogen than oxygen.
What are the name of the electrodes in electrolysis?
negative electrode is called the CATHODE because it attracts the CATIONS (positive ions)
positive electrode is called the ANODE because it attracts the ANIONS (negative ions)
