Half Equations & Ionic Equations Flashcards

All 6 cards in this deck

What is a half equation? (HT)

An equation showing the electrons lost or gained by one species, e.g. at an electrode.

What is an ionic equation? (HT)

An equation showing only the ions and substances that actually take part in the reaction, with spectator ions left out.

What is a spectator ion? (HT)

An ion that is unchanged in the reaction and appears on both sides, so it is left out of the ionic equation.

What are the steps to write a half equation for a metal ion gaining electrons at the cathode? (HT)
e.g. $Cu^{2+}$ forming copper

1. Write the ion on the left: $Cu^{2+}$.
2. Add electrons on the left to cancel the charge: $Cu^{2+} + 2e^-$.
3. Write the neutral product on the right: $Cu^{2+} + 2e^- \rightarrow Cu$.

What are the steps to write an ionic equation? (HT)
e.g. $HCl + NaOH \rightarrow NaCl + H_2O$

1. Write all aqueous compounds as separate ions: $H^+ + Cl^- + Na^+ + OH^- \rightarrow Na^+ + Cl^- + H_2O$.
2. Cancel ions that appear unchanged on both sides: $Na^+$ and $Cl^-$.
3. Write what is left: $H^+ + OH^- \rightarrow H_2O$.

True or false? In the half equation $Na \rightarrow Na^+ + e^-$, the sodium atom has gained an electron. (HT)

False. It has lost one electron — electrons on the right means loss (oxidation).