Chem: Electrolysis

What is electrolysis?

The breaking down of a substance using electricity, where an electric current is passed through an electrolyte, causing it to decompose.

What occurs at the cathode and anode during electrolysis?

Positive ions (cations) move to the negative electrode (cathode) and are reduced; negative ions (anions) move to the positive electrode (anode) and are oxidised.

What is an ionic half equation used for?

To show how electrons are transferred during reactions at each electrode.

Why can molten ionic compounds be electrolysed?

The ions can move freely because the compound is molten or dissolved.

What happens during the electrolysis of molten lead bromide ($PbBr_2$)?

Lead ions ($Pb^{2+}$) are attracted to the negative cathode where they gain two electrons to form lead atoms; bromide ions ($Br^-$) are attracted to the positive anode where they lose electrons to form bromine molecules.

Why are electrodes made from an inert (unreactive) material?

So they do not take part in the chemical reaction.

What is an electrochemical cell?

A circuit made up of the anode, cathode, electrolyte, a power source, and the wires connecting the two electrodes.

What ions are present in aqueous solutions alongside those from the dissolved ionic compound?

Hydrogen ions ($H^+$) and hydroxide ions ($OH^-$) from water.

How do you determine what is produced at the cathode during the electrolysis of an aqueous solution?

If $H^+$ ions and metal ions are present, hydrogen gas is produced if the metal is more reactive than hydrogen; if the metal is less reactive than hydrogen, a solid layer of the pure metal is produced instead.

How do you determine what is produced at the anode during the electrolysis of an aqueous solution?

If $OH^-$ and halide ions ($Cl^-$, $Br^-$, $I^-$) are present, halogen molecules are formed; if no halide ions are present, oxygen gas is formed.