Electrolytes and non-electrolytes
Before studying electrolysis we need to know which liquids and solutions conduct electricity at all. Activity 12.2.1 tests several.
Activity 12.2.1
You will need: carbon electrodes, two torch cells (1.5 V), connecting wires, a galvanometer, several beakers, 50 cm3 each of coconut oil, kerosene, distilled water, acidified water, salt solution and ethanol
Set up the circuit of figure 12.2.1. Dip the carbon electrodes in each liquid in turn and watch whether the meter deflects. Report what you see.
Figure to be added
The observation
The meter deflects only with the acidified water and the salt solution. So only those liquids conduct electricity.
Electrolytes — conduct
Aqueous ionic compounds: aqueous sodium chloride, aqueous copper sulphate
Molten ionic compounds: sodium chloride melted by heating
Acid solutions: aqueous hydrochloric acid, aqueous sulphuric acid
Base solutions: aqueous sodium hydroxide, lime water
Non-electrolytes — do not
Pure (distilled) water
Organic liquids: petrol, kerosene, paraffin, hexane
Why ions matter
In a solid ionic crystal the oppositely charged ions are held in place and cannot move, so the solid does not conduct. Dissolved in water, or melted by heating, the ions become free to move, and the liquid conducts. Petrol, kerosene and paraffin are covalent hydrocarbons with no ions, so they do not conduct; pure water is covalent and has almost no ions, so distilled water does not conduct either. Acids such as HI, HCl and H2SO4 are covalent too, but in water their bonds break to form ions, so their solutions conduct.
HCl → H+ (aq) + Cl- (aq)
H2SO4 → 2H+ (aq) + SO42- (aq)
in water
Electrolyte
A liquid or solution that conducts electricity is an electrolyte; one that does not is a non-electrolyte.
Solid salt does not conduct
Sodium chloride conducts when it is dissolved or molten, but a dry crystal of it does not: the ions are there, but they cannot move.