Define buffer solution by describing how it responds when small amounts of acid or alkali are added.
Write equations showing how this solution behaves as a buffer when dilute aqueous sodium hydroxide is added.
Write equations showing how this solution behaves as a buffer when dilute aqueous nitric acid is added.
Calculate the $\text{H}^+$ concentration and the $\text{C}_6\text{H}_5\text{COOH}$ concentration in the buffer solution described. Use the expression for the $K_a$ of $\text{C}_6\text{H}_5\text{COOH}$ to determine the concentration of $\text{C}_6\text{H}_5\text{COO}^-\text{Na}^+$ in the buffer solution. Show your working and give each answer to a minimum of three significant figures.
A $10.0\,\text{cm}^3$ portion of the buffer solution is combined with $10.0\,\text{cm}^3$ of $1.00\,\text{mol dm}^{-3}$ KOH. Both solutions start at $298\,\text{K}$. The mixture is allowed to react without stirring. Two observations are made: once the reaction has finished, the temperature is fractionally above $298\,\text{K}$; after the reaction, the pH is greater than $13$. Explain these two observations.
Magnesium benzoate, $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$, has a solubility in water of less than $1.00\,\text{g dm}^{-3}$ at $298\,\text{K}$. $K_{sp} = [\text{Mg}^{2+}][\text{C}_6\text{H}_5\text{COO}^-]^2 = 1.76 \times 10^{-7}$ at $298\,\text{K}$. Calculate the solubility of $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$ in water at $298\,\text{K}$. Give your answer in $\text{g dm}^{-3}$. $M_r\!:\;\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2 = 266.3$. Show your working.
An excess of $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$ is added to a sample of $0.50\,\text{mol dm}^{-3}$ $\text{MgSO}_4$ at $298\,\text{K}$. State whether the equilibrium concentration of $\text{Mg}(\text{C}_6\text{H}_5\text{COO})_2$ is higher than, the same as, or lower than the value found in (i). Explain your answer.