10 - Electrolytic Processes Flashcards
What is an electrolyte?
Ionic compounds in the molten state or dissolved in water
What is electrolysis?
A process in which electrical energy, from a direct current supply, decomposes electrolytes
What happens to an ionic solid when it’s dissolved in water?
Its ionic bonds break
Describe the movement of ions during electrolysis
- Cations migrate to the negatively charged cathode
- Anions migrate to the positively charged anode
What are Cations?
Positive ions that are attracted to the negative cathode
What are Anions?
Negative ions that are attracted to the positive anode
What is an electrode?
A rod made of a metal or graphite that carries the current into or out of the electrolyte
What is oxidation?
Loss of electrons
What is Reduction?
Gain of electrons
What acronym is used to remember oxidation & reduction?
OILRIG
What reaction occurs at the Anode?
Oxidation
What reaction occurs at the Cathode?
Reduction
Can covalent compounds undergo electrolysis?
They cannot conduct electricity hence they do not undergo electrolysis
What is the effect of the transfer of electrons during **electrolysis?
It changes charged ions into atoms or molecules, resulting in chemical changes at the electrodes
How can the chemical changes at each electrode be represented by?
Half equations
Core practical: Electrolysis of copper sulfate solution
How do you set up this practical?
What is the method for this practical?
1) Use 2 pieces of copper foil (1 labelled anode and the other cathode). Measure & record masses of both electrodes
2) Set up an electrolysis circuit
3) Turn on power & adjust variable resistor to a constant current. Leave the power on for a certain time frame
4) Turn off the power & remove electrodes from the beaker. Wash electrodes w/ distilled water & dip into propanone
5) Measure & record the masses of the dry electrodes
6) Repeat the experiment w/ diff currents
How can we predict the electrolysis products of any molten salts?
- Salt will always decompose into elements
- Metal is produced at cathode & non-metal at the anode
What is the electrolysis of molten or dissolved ionic salts carried out using?
Inert electrodes
Why are inert electrodes used in the electrolysis of molten or dissolved ionic salts?
They are used to avoid any unwanted chemical reactions with the electrodes themselves
—> Can interfere with desired result
Why are there some hydrogen & hydroxide ions in an aqueous solution of a salt?
As water ionises to a very small extent
What products are formed in the electrolysis of copper chloride solution?
- Product at Anode : Chlorine gas released
- Product at Cathode : Copper is discharged as a metal
Why is hydrogen gas not released in the electrolysis of copper chloride solution?
Copper is below hydrogen so copper ions are preferentially discharged at the cathode
What products are formed in the electrolysis of sodium chloride solution?
- Product at Anode : Chlorine gas released
- Product at Cathode : Hydrogen gas released
What products are formed in the electrolysis of sodium sulphate solution?
- Product at Anode : Oxygen gas released
- Product at Cathode : Hydrogen gas released
Why is oxygen gas released in the electrolysis of sodium sulphate solution?
Hydroxide ions are preferentially discharged over sulphate ions, so oxygen is produced at the anode
What products are formed in the electrolysis of water acidified with sulfuric acid?
- Product at Anode : Oxygen gas released
- Product at Cathode : Hydrogen gas released
Why is oxygen gas released in the electrolysis of dilute sulphuric acid?
Oxygen from water molecules is preferentially discharged at the anode
Why is hydrogen gas released in the electrolysis of sodium sulphate & sodium chloride?
Sodium is above hydrogen so hydrogen ions are preferentially discharged at the cathode
Describe the apparatus used in the electrolysis of an aqueous solution where there are gaseous products
