Problem 1
The values of \(\mathrm{p} K_{\mathrm{a}}(1)\) and \(\mathrm{p} K_{\mathrm{a}}(2)\) for chromic acid \(\left(\mathrm{H}_{2} \mathrm{Cr} \mathrm{O}_{4}\right)\) are 0.74 and 6.49 respectively. (a) Determine values of \(K_{\mathrm{a}}\) for each dissociation step. (b) Write equations to represent the dissociation steps of chromic acid in aqueous solution.
Problem 2
Four \(\mathrm{p} K_{\mathrm{a}}\) values (1.0,2.0,7.0,9.0) are tabulated for the acid \(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{7}\). Write equations to show the dissociation steps in aqueous solution and assign, with reasoning, a \(\mathrm{p} K_{\mathrm{a}}\) value to each step.
Problem 3
The values of \(\mathrm{p} K_{\mathrm{a}}\) for \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}\) and \(\mathrm{CF}_{3} \mathrm{CO}_{2} \mathrm{H}\) are 4.75 and \(0.23,\) both of which are very nearly independent of temperature. Suggest reasons for this difference.
Problem 4
(a) To what equilibria do the values of \(\mathrm{p} K_{\mathrm{a}}(1)=10.71\) and \(\mathrm{p} K_{\mathrm{a}}(2)=7.56\) for the conjugate acid of \(\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\) refer? (b) Calculate the corresponding values of \(\mathrm{p} K_{\mathrm{b}}\) and write equations to show the equilibria to which these values refer.
Problem 7
When NaCN dissolves in water, the resulting solution is basic. Account for this observation given that \(\mathrm{p} K_{\mathrm{a}}\) for \(\mathrm{HCN}\) is 9.31.
Problem 8
Write equations to illustrate the amphoteric behaviour of \(\left[\mathrm{HCO}_{3}\right]^{-}\) in aqueous solution.
Problem 9
Which of the following oxides are likely to be acidic, basic or amphoteric in aqueous solution: (a) \(\mathrm{MgO}\) (b) \(\operatorname{Sn} \mathrm{O} ;(\mathrm{c}) \mathrm{CO}_{2} ;(\mathrm{d}) \mathrm{P}_{2} \mathrm{O}_{5}\) (e) \(\mathrm{Sb}_{2} \mathrm{O}_{3} ;(\mathrm{f}) \mathrm{SO}_{2} ;(\mathrm{g}) \mathrm{Al}_{2} \mathrm{O}_{3}\) (h) \(\mathrm{BeO} ?\)
Problem 10
Explain what is meant by the terms (a) saturated solution; (b) solubility; (c) sparingly soluble salt; (d) solubility product (solubility constant).
Problem 11
Write down expressions for \(K_{\mathrm{sp}}\) for the following ionic salts: (a) AgCl; (b) \(\mathrm{CaCO}_{3} ;\) (c) \(\mathrm{CaF}_{2}\).
Problem 14
Outline the changes that occur (a) to the salt, and (b) to the water molecules, when solid NaF dissolves in water. How do these changes affect (qualitatively) the entropy of the system?
