Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

Ammonium nitrate is an important fertiliser formed through the acid-base reaction of ammonia with nitric acid.
(a)[1]

Write the equation for making ammonium nitrate from ammonia and nitric acid.

(b(i))[2]

Draw a second line on the axes above to represent the energy distribution in the same gas mixture at a higher temperature.

(b(ii))[2]

Using the two curves, explain why ammonia would be produced faster at a higher temperature.

(b(iii))[2]

Put an appropriate label on the horizontal axis above and use it to explain why a catalyst is employed in the Haber process.

(b)

Ammonia for this reaction is made by the Haber process and nitric acid is made by oxidation of ammonia. In the Haber process, nitrogen and hydrogen react at a temperature of $450\degree\text{C}$ and a pressure of $20\,000\,\text{kPa}$. If the reaction temperature is higher, ammonia would be produced at a faster rate. The equation for the Haber process is: $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \quad \Delta H = -92\,\text{kJ mol}^{-1}$ The Boltzmann distribution curve shows the energy distribution in a mixture of nitrogen and hydrogen at $450\degree\text{C}$.

(b(iv))[2]

Explain why a higher temperature is not chosen even though it would increase the rate of ammonia production.

(c)[3]

The first step in making nitric acid is the reaction of ammonia with oxygen to produce nitrogen monoxide, $\text{NO}$, and water. Suggest an equation for this reaction and use oxidation numbers to show that it is a redox reaction.

(d(i))[2]

Draw a dot-and-cross diagram for the ammonium ion. Show only the outer electrons. Use the following code for your electrons. • electrons from nitrogen \times electrons from hydrogen

(d(ii))[2]

State the shape of an ammonium ion and give the H-N-H bond angle.

(e)[3]

State and explain the problems caused when ammonium nitrate fertiliser is overused and the excess is washed into rivers.

Worked solution & mark scheme

This 19-mark question has a full step-by-step worked solution and mark scheme. One marking point: $\mathrm{NH_3 + HNO_3 \rightarrow NH_4NO_3}$

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