Define the meaning of transition element.
Write out the electronic configuration of an isolated gaseous $\text{Fe}^{3+}$ ion: $1s^2\,\ldots$
Name two transition elements whose isolated gaseous atoms contain the same number of electrons in the $3d$ subshell as an isolated gaseous $\text{Fe}^{3+}$ ion.
Cobalt(II) sulfate is mixed with water to give a pink solution containing complex ion $P$. An excess of concentrated hydrochloric acid is then added to this solution to produce a blue solution containing complex ion $Q$. Finish the diagram to show the three-dimensional structure of $Q$. State the charge on this complex ion.
Name the reaction type in which $P$ is converted into $Q$.
Explain why solutions containing transition element ions are often coloured.
Explain why $P$ and $Q$ have different colours.
Cobalt undergoes two reaction types in this reaction. One of them is the same as the one described in c(ii). Name the other reaction type that cobalt undergoes.
Draw the three-dimensional structures of the two isomeric complexes in the boxes. You may use a simplified diagram to represent one molecule of $\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2$.
Name the type of stereoisomerism shown by these two isomeric complexes.
State the co-ordination number of cobalt in these two isomeric complexes.
Write an expression for the $K_{\text{stab}}$ of $[\text{Hg(CN)}_4]^{2-}$.
An aqueous solution of $\text{Hg}^{2+}$ is added to a solution that already contains equal concentrations of $\text{CN}^-(aq)$, $\text{Cl}^-(aq)$ and $\text{I}^-(aq)$. The mixture is then allowed to reach equilibrium. Predict which of $[\text{Hg(CN)}_4]^{2-}$, $[\text{HgCl}_4]^{2-}$ and $[\text{HgI}_4]^{2-}$ will be present in the mixture at the highest concentration and which will be present at the lowest concentration. Explain your answer.