Chemistry 9701 · AS & A Level · Chemistry of transition elements
Chemistry of transition elements — practice question
Several isomers with the formula $\text{Cr(H}_2\text{O)}_6\text{Cl}_3$ are known. Their overall formula is $[\text{Cr(H}_2\text{O)}_{6-n}\text{Cl}_n]\text{Cl}_{3-n} \cdot n\text{H}_2\text{O}$. In each case, a Cr(III) ion is six-co-ordinated in an octahedral complex. Water molecules that are not bonded directly to the Cr atom remain in the crystal lattice as water of crystallisation. The Cr-Cl bond is difficult to break, so chloride bonded to the Cr(III) ion in the complex does not react.
$1.00\,\text{g}$ samples of three isomers, $\text{A}$, $\text{B}$ and $\text{C}$, were dissolved separately in water. An excess of $\text{AgNO}_3(aq)$ was then added to each sample and the mass of $\text{AgCl}(s)$ formed was measured.
$\text{Ag}^+(aq) + \text{Cl}^-(aq) \rightarrow \text{AgCl}(s)$
(a(i))[1]
Calculate the $M_r$ for $\text{Cr(H}_2\text{O)}_6\text{Cl}_3$.
(a(ii))[2]
Use the information in the table above to calculate the value of $n$ for each isomer, $\text{A}$, $\text{B}$ and $\text{C}$. Fill in the table below with the values of $n$ and the molecular formula of each isomer, following the pattern of the general formula shown above. Show your working for at least one calculation of $n$.
(b(i))[1]
Name the type of isomerism that is shown by $\text{Ni(R}_3\text{P)}_2(\text{CN})_2$.
(b(ii))[1]
Draw the structures for these two isomers.
(b(iii))[1]
State which isomer has a dipole moment. Then Explain your answer.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Hence, $M_r = 266.5$.” …