Half Equations in Electrolysis Flashcards

All 6 cards in this deck

At the cathode, what happens to the positive ions and what type of reaction is this?

They gain electrons, so the reaction is reduction.

At the anode, what happens to the negative ions and what type of reaction is this?

They lose electrons, so the reaction is oxidation.

What are the steps to write the half equation for a metal formed at the cathode?
e.g. $\mathrm{Al^{3+}}$ ions in molten aluminium oxide

1. Write the metal ion on the left and the metal atom on the right: $\mathrm{Al^{3+}} \rightarrow \mathrm{Al}$
2. Add electrons to the left, one for each positive charge: $\mathrm{Al^{3+}} + 3\mathrm{e^-} \rightarrow \mathrm{Al}$

What are the steps to write the half equation for a halogen formed at the anode?
e.g. bromide ions, $\mathrm{Br^-}$

1. Two halide ions give one diatomic molecule: $2\mathrm{Br^-} \rightarrow \mathrm{Br_2}$
2. Add electrons to the right, one for each negative charge: $2\mathrm{Br^-} \rightarrow \mathrm{Br_2} + 2\mathrm{e^-}$

What is the half equation for oxygen being produced from hydroxide ions at the anode?

$4\mathrm{OH^-} \rightarrow \mathrm{O_2} + 2\mathrm{H_2O} + 4\mathrm{e^-}$

True or false? In a half equation for the cathode reaction, the electrons are written on the right-hand side.

False. Electrons are gained at the cathode, so they are written on the left, e.g. $\mathrm{Na^+} + \mathrm{e^-} \rightarrow \mathrm{Na}$