Draw dot-and-cross diagrams for these two acids, showing only outer-shell electrons, for HOCN(cyanic acid) and HNCO (isocyanic acid).
Suggest the bond-angle values for HNC and NCO in isocyanic acid.
Suggest which acid, cyanic or isocyanic, has the shorter $\text{C-N}$ bond length. Explain your answer.
Isocyanic acid is a weak acid. $\text{HNCO} \rightleftharpoons \text{H}^+ + \text{NCO}^- \quad K_a = 1.2 \times 10^{-4}\,\text{mol dm}^{-3}$. Calculate the pH of a $0.10\,\text{mol dm}^{-3}$ solution of isocyanic acid.
Sodium cyanate, $\text{NaNCO}$, is used in the manufacture of isocyanic acid. Sodium cyanate is made commercially by reacting urea, $(\text{NH}_2)_2\text{CO}$, with sodium carbonate. The other products in this reaction are carbon dioxide, ammonia and steam. Write an equation for making $\text{NaNCO}$ by this route.
Barium hydroxide, $\text{Ba(OH)}_2$, is completely ionised in aqueous solution. When $30.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ $\text{Ba(OH)}_2$ is added to $20.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ isocyanic acid, the pH is measured. Calculate the $[\text{OH}^-]$ at the end of the addition.
Use your answer to (i) to find $[\text{H}^+]$ and the pH of the solution at the end of the addition.
On the axes below, sketch the change in pH as a total of $30.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ $\text{Ba(OH)}_2$ is added to $20.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ isocyanic acid.
The cyanate ion, $\text{NCO}^-$, can act as a monodentate ligand. State what is meant by the terms monodentate and ligand.
Silver ions, $\text{Ag}^+$, react with cyanate ions to form a linear complex. Suggest the formula of this complex, including its charge.
When heated with $\text{HCl(aq)}$, organic isocyanates, RNCO, are hydrolysed to the amine salt, $\text{RNH}_3\text{Cl}$, and $\text{CO}_2$. $\text{RNCO} + \text{H}_2\text{O} + \text{HCl} \rightarrow \text{RNH}_3\text{Cl} + \text{CO}_2$ A $1.00\,\text{g}$ sample of an organic isocyanate, RNCO, was treated in this way, and the $\text{CO}_2$ produced was absorbed in an excess of aqueous $\text{Ba(OH)}_2$ according to the equation shown. The solid $\text{BaCO}_3$ formed weighed $1.66\,\text{g}$. $\text{Ba(OH)}_2\text{(aq)} + \text{CO}_2\text{(g)} \rightarrow \text{BaCO}_3\text{(s)} + \text{H}_2\text{O(l)}$ Calculate the number of moles of $\text{BaCO}_3$ produced.
Hence calculate the $M_r$ of the organic isocyanate RNCO.
The R group in RNCO and $\text{RNH}_3\text{Cl}$ contains only carbon and hydrogen. Use your $M_r$ value from (ii) to suggest the molecular formula of the organic isocyanate RNCO.
Suggest a possible structure of the amine $\text{RNH}_2$, which forms the amine salt, $\text{RNH}_3\text{Cl}$.
Suggest a possible structure of the amine RNH$_2$, which forms the amine salt, RNH$_3$Cl.