Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

Examples of molecular ions include species such as $\text{NH}_4^+$, $\text{CO}_3^{2-}$ and $\text{PO}_4^{3-}$.
(a)[2]

Ionic and covalent bonds both rely on electrostatic attraction between different species. Identify which species are attracted electrostatically to each other in: • an ionic bond • a covalent bond.

(b)[3]

Complete Table 1.1 so that it shows the overall numbers of protons and electrons in the molecular ions $\text{NH}_4^+$, $\text{CO}_3^{2-}$ and $\text{PO}_4^{3-}$.

(c(i))[1]

$\text{NH}_4^+$ is a Brønsted-Lowry acid. Define Brønsted-Lowry acid.

(c(ii))[1]

When $\text{NH}_4^+$(aq) is heated with $\text{NaOH}$(aq), a pungent gas is formed. Write an ionic equation for this reaction.

(c(iii))[2]

The nitrogen atom in $\text{NH}_4^+$ is $sp^3$ hybridised. $sp^3$ orbitals are produced by mixing one $2s$ and three $2p$ orbitals. Sketch the shapes of a $2s$ and a $2p_x$ orbital on the axes in Fig. 1.1.

(d(i))[1]

Many naturally occurring hydrated compounds contain the anion $\text{PO}_4^{3-}$. Name the anion $\text{PO}_4^{3-}$.

(d(ii))[2]

Struvite is a soft hydrated mineral with $M_r = 245.3$. Its anhydrous form has the formula $\text{NH}_4\text{MgPO}_4$. Calculate the number of molecules of water of crystallisation in struvite. Give your answer to the nearest integer. Show your working.

(e(i))[3]

$\text{OH}^-$(aq) reacts with 2-bromo-2-methylpropane in an $S_N1$ reaction. The molecular ion $(\text{CH}_3)_3\text{C}^+$ forms as the intermediate in this reaction. Draw the mechanism for the $S_N1$ reaction of $\text{OH}^-$ with 2-bromo-2-methylpropane. Include charges, dipoles, lone pairs of electrons and curly arrows as appropriate. Draw the structures of the organic reactant and organic product.

(e(ii))[1]

2-bromo-2-methylpropane is a tertiary bromoalkane. Define tertiary bromoalkane.

(e(iii))[1]

Organic compound $M$ is formed when 2-bromo-2-methylpropane is heated with ethanolic $\text{OH}^-$. Draw the structure of $M$.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: Ionic bonding is the attraction between oppositely charged ions, namely cations and anions

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