Chemistry 9701/41 — October/November 2012

Write down what you would see, and write equations for the reactions that occur, when silicon(IV) chloride and phosphorus(V) chloride are separately mixed with water.

silicon(IV) chloride

phosphorus(V) chloride

Iron(III) chloride, $\text{FeCl}_3$, is used to dissolve unwanted copper from printed circuit boards (PCBs) by the following reaction.

A solution in which $[\text{Fe}^{3+}(\text{aq})]$ was originally equal to $1.50\text{ mol dm}^{-3}$ was re-used several times to dissolve copper from the PCBs, and was then titrated as follows.

A $2.50\text{ cm}^3$ sample of the partially-used-up solution was acidified and titrated with $0.0200\text{ mol dm}^{-3}$ $\text{KMnO}_4$.
This oxidised any $\text{FeCl}_2$ in the solution back to $\text{FeCl}_3$.
It was found that $15.0\text{ cm}^3$ of $\text{KMnO}_4(\text{aq})$ was required to reach the end point.

When $\text{SiCl}_4$ vapour is passed over $\text{Si}$ at red heat, $\text{Si}_2\text{Cl}_6$ is formed. $\text{Si}_2\text{Cl}_6$ contains a $\text{Si-Si}$ bond.
The reaction of $\text{Si}_2\text{Cl}_6$ and $\text{Cl}_2$ re-forms $\text{SiCl}_4$.

Use bond energy data from the Data Booklet to calculate $\Delta H^\ominus$ for this reaction.

Calcium forms three calcium silicides, $\text{Ca}_2\text{Si}$, $\text{CaSi}$ and $\text{CaSi}_2$. The first of these reacts with water as follows.