In water, hydrogen fluoride, HF, acts as a weak acid, with $K_a = 5.6 \times 10^{-4}\,\text{mol dm}^{-3}$. Find the pH of a $0.050\,\text{mol dm}^{-3}$ HF solution.
Gaseous ammonia and hydrogen fluoride combine to form solid ionic ammonium fluoride. $\text{NH}_3(g) + \text{HF}(g) \rightleftharpoons \text{NH}_4\text{F}(s) \quad \Delta H = -147\,\text{kJ mol}^{-1}$. What sort of reaction is this?
Draw dot-and-cross diagrams (outer shells only) to show the bonding in the three compounds in this reaction: $\text{NH}_3$, $\text{HF}$ and $\text{NH}_4\text{F}$.
There are three bonding types in $\text{NH}_4\text{F}$. Name each one and say where in the compound it appears.
The reaction between $\text{NH}_3$ and HF is reversible. Which temperature and pressure conditions would favour the reverse reaction, that is, the dissociation of $\text{NH}_4\text{F}$? Explain your answer.
Many commercial copper and brass polishes contain ammonia. The tarnish that appears on copper is often copper sulfide, $\text{CuS}$. In air, $\text{O}_2$ can react with this copper sulfide in the presence of $\text{NH}_3$ to form the soluble cuprammonium sulfate, $[\text{Cu}(\text{NH}_3)_4]\text{SO}_4$. Write an equation for this reaction.
State the colour of cuprammonium sulfate solution.
Describe what you would observe if water were added to a cuprammonium sulfate solution. Explain your answer.
Adding sulfuric acid to $\text{Cu}^{2+}(aq)$ produces no colour change, but adding concentrated hydrochloric acid to $\text{Cu}^{2+}(aq)$ changes the solution to yellow-green. When the solution is then diluted with water, it returns to its original colour. Suggest the reaction type involved with $\text{HCl}(aq)$, say what is formed, and give an equation for the change.