Two of the $3d$ orbitals are the $3d_{xy}$ orbital and the $3d_{z^2}$ orbital. Sketch the shapes of these two orbitals.
The $\text{Ni}^{2+}$ ion forms many different complexes. A solution containing the $[\text{Ni}(\text{H}_2\text{O})_6]^{2+}$ complex ion is green. When an excess of $1,2$-diaminoethane, $en$, $\text{H}_2\text{NCH}_2\text{CH}_2\text{NH}_2$, is added, the solution changes colour to blue. This happens because the $[\text{Ni}(en)_3]^{2+}$ complex ion is formed. Explain why the two solutions have colour, and why the colours are not the same.
The $\text{[Ni(en)}_3]^{2+}$ complex may occur as a mixture of two stereoisomers. Finish the three-dimensional diagram to show one stereoisomer. Each $en$ ligand may be shown as $\ce{N-CH2CH2-N}$.
Name the geometry of the complex ion drawn in (b)(ii) and the type of stereoisomerism shown by $\text{[Ni(en)}_3]^{2+}$. Geometry ________. Stereoisomerism shown ________.
Iron(II) carbonate, $\ce{FeCO3}$, and nickel(II) carbonate, $\ce{NiCO3}$, both decompose on heating. $\ce{FeCO3}$ decomposes at a lower temperature than $\ce{NiCO3}$. Suggest a possible explanation for this difference. Explain your answer.
Describe the colour change observed in the conical flask at the end-point of this titration. The colour changes from ________ to ________.
Calculate the percentage by mass of iron in A. $A_r$: $\ce{Fe}$, $55.8$.