C6 - Electrolysis
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define electrolysis
the chemical process of splitting an ionic compound using electricity
Why can’t ionic compounds be electrolysed when they are solid?
solid ionic compounds don’t conduct electricity
define half equation
an equation that shows the movement of ions and electrons
define electrolyte
the substance that is being split
define electrode
a conductor through which electricity enters or leaves an object, substance, or region
define cathode in electrolysis
negatively charged electrode
define anode electrolysis
positively charged electrode
define cation
positively charged ion, it is attracted to the cathode
define anion
negatively charged ion, it is attracted to the anode
show the dissociation of water
H2O ⇌ H+ + OH-
During electrolysis, what is the rule that determines what is discharged at the cathode?
The LESS reactive element will be attracted to the cathode, the MORE reactive element will stay in the solution.
During electrolysis, what is the rule that determines what is discharged at the anode?
• Halide - any halogen • Hydroxide - OH- • Other - any other anion
What is discharged if hydroxide ions are attracted to the anode? half equation
water and oxygen 4OH- (aq) → 2H2O (l) + O2 (g) + 4e-
How do you test for chlorine gas?
Hold blue litmus paper above the gas. The paper will turn red and then white (because it is bleached) if the gas is chlorine.
What forms at the anode and cathode during the electrolysis of copper sulfate solution?
Cathode - copper. It is less reactive than hydrogen Anode - oxygen. Sulfate is not a halide so the hydroxide is attracted to the anode causing it to form oxygen.
Why are electrodes made of carbon (graphite)
Graphite is conductive and inert, so it does not react with the ions in the electrolyte.
purpose of cryolite when extracting aluminum oxide
to lower the melting point, so less energy required