Explain why Group 2 nitrates become more thermally stable down the group.
Sodium nitrite, $\text{NaNO}_2$, is formed when sodium nitrate, $\text{NaNO}_3$, is heated and decomposes. A student examined a sample of sodium nitrite by titrating it with aqueous cerium(IV) ions, $\text{Ce}^{4+}(\text{aq})$. The titration equation is shown below. $\text{NO}_2^-(\text{aq}) + 2\text{Ce}^{4+}(\text{aq}) + \text{H}_2\text{O}(\text{l}) \rightarrow 2\text{Ce}^{3+}(\text{aq}) + \text{NO}_3^-(\text{aq}) + 2\text{H}^+(\text{aq})$. $0.138\,\text{g}$ of impure sodium nitrite was dissolved in water and diluted to $100\,\text{cm}^3$ in a volumetric flask. A $25.0\,\text{cm}^3$ portion of this solution needed $21.80\,\text{cm}^3$ of $0.0400\,\text{mol dm}^{-3}$ $\text{Ce}^{4+}(\text{aq})$ to reach the end-point. Assume the impurity does not react with $\text{Ce}^{4+}(\text{aq})$. Calculate the percentage purity of the sodium nitrite sample.
Acidified manganate(VII) ions, $\text{MnO}_4^-(\text{aq})$, may also be used to test solutions that contain nitrite ions, $\text{NO}_2^-$. In acidic solution, $\text{NO}_2^-$ ions are present as $\text{HNO}_2$. Use the Data Booklet to build an ionic equation for this reaction.
Use the $E^\circ$ values to find the $E^\circ_{\text{cell}}$ for this reaction.
Nitrous acid, $\text{HNO}_2$, is a weak acid with a $K_a$ of $6.9 \times 10^{-4}\,\text{mol dm}^{-3}$ at $298\,\text{K}$. Explain the difference between a strong acid and a weak acid.
Write the expression for the acid dissociation constant, $K_a$, for $\text{HNO}_2$.
Calculate the pH of $0.15\,\text{mol dm}^{-3}$ $\text{HNO}_2$.
Calculate the percentage of $\text{HNO}_2$ molecules that are ionised in $0.15\,\text{mol dm}^{-3}$ $\text{HNO}_2$.
Solutions containing a mixture of $\text{HNO}_2$ and $\text{NaNO}_2$ are buffer solutions. Define what is meant by the term buffer solution.
Write two equations to show how a solution containing a mixture of $\text{HNO}_2$ and $\text{NaNO}_2$ acts as a buffer.
Suggest the reagent used in reaction 1.
Suggest structures of compounds Y and Z and draw them in the boxes above.
Predict the number of peaks in the carbon-13 NMR spectra of W and Z.