Explain why chromium complexes show colour.
Anhydrous chromium(III) chloride can produce four different compounds when it reacts with water under different conditions. If separate samples of each compound are treated with aqueous silver nitrate, differing amounts of silver chloride are formed. The precipitation leaves the complex ions $P$, $Q$, $R$ and $S$ in solution. Draw three-dimensional diagrams for complex ions $P$, $Q$, $R$ and $S$, and show the charge on each ion.
When anhydrous chromium(III) chloride reacts with water under different conditions, four distinct compounds are obtained. If each compound is then treated separately with aqueous silver nitrate, varying amounts of silver chloride are produced. The precipitation leaves the complex ions P, Q, R and S in solution.
Suggest why complex ion S has no overall dipole.
The structure of picolinic acid is shown. Its conjugate base is a bidentate ligand, Z.
Define the term bidentate ligand.
Draw the structure corresponding to Z.
Z reacts with aqueous chromium(III) ions, $[\text{Cr(H}_2\text{O)}_6]^{3+}$, in a $3:1$ ratio to make a new neutral complex. State the coordination number and the geometry around the chromium(III) centre in the complex.
On heating, $(\text{NH}_4)_2\text{Cr}_2\text{O}_7$ decomposes readily to give $\text{Cr}_2\text{O}_3$, steam and an inert colourless gas.
Deduce the oxidation numbers for chromium in $(\text{NH}_4)_2\text{Cr}_2\text{O}_7$ and in $\text{Cr}_2\text{O}_3$.
Construct an equation showing the thermal decomposition of $(\text{NH}_4)_2\text{Cr}_2\text{O}_7$.