Chemistry 9701/41 — May/June 2011

Cambridge A-Level · worked solutions for every part, with the mark scheme

questions

100

marks

120

minutes

Topics Equilibria · Halogen Compounds · Reaction Kinetics · Carboxylic Acids and Derivatives · Hydrocarbons · Introduction to A Level Organic Chemistry · +5 more

Q1Chemical EnergeticsNitrogen CompoundsFree sample

Taken together, nitrogen and oxygen make up 99% of the air. Oxygen is by far the more reactive of the two gases, and most of the substances that react with air combine with the oxygen rather than with the nitrogen.

(a)

State one reason why the molecule of nitrogen, $\text{N}_2$ , is so unreactive.

(b)

Despite the apparent lack of reactivity of $\text{N}_2$ , nitrogen atoms have been found to form bonds with almost all of the elements in the Periodic Table. Lithium metal reacts with nitrogen gas at room temperature to give lithium nitride, $\text{Li}_3\text{N}$ . Magnesium produces magnesium nitride, $\text{Mg}_3\text{N}_2$ , as well as magnesium oxide, when heated in air.

Calculate the lattice energy of magnesium nitride using the following data, in addition to relevant data from the Data Booklet.

enthalpy change	value/ $\text{kJ mol}^{-1}$
atomisation of $\text{Mg(s)}$	+148
total of electron affinities for the change $\text{N(g)} \rightarrow \text{N}^{3-}\text{(g)}$	+2148
enthalpy of formation of $\text{Mg}_3\text{N}_2\text{(s)}$	–461

lattice energy = ........................... $\text{kJ mol}^{-1}$

(c)

Lithium reacts readily with nitrogen, and because of this $\text{Li}_3\text{N}$ has been considered as a possible intermediate in the ‘fixing’ of nitrogen to make ammonia-based fertilisers.

\text{N}_2\text{(g)} \xrightarrow{+\text{ Li}} \text{Li}_3\text{N} \xrightarrow{+\text{ H}_2\text{O}} \text{NH}_3 + \mathbf{A}

(i)

Construct an equation for the reaction between $\text{Li}_3\text{N}$ and $\text{H}_2\text{O}$ , and hence identify compound A.

(ii)

Using your knowledge of the Haber process, consider one advantage and one disadvantage of using lithium as a means of fixing nitrogen, rather than the Haber process.

advantage of the lithium method

..................................................................................................................................

disadvantage of the lithium method

..................................................................................................................................

(d)

Another possible advantage of $\text{Li}_3\text{N}$ is that it contains a large percentage by mass of nitrogen. Another fertiliser that contains a large percentage by mass of nitrogen is urea, $\text{NH}_2\text{CONH}_2$ .

(i)

Calculate and compare the percentages by mass of nitrogen in $\text{Li}_3\text{N}$ and $\text{NH}_2\text{CONH}_2$ .

(ii)

What class of organic compound is urea?

(iii)

Write an equation for the production of ammonia by the reaction between urea and water.

(iv)

Urea can be applied directly to the soil either before or during the growing of crops.
What would be a major disadvantage of using lithium nitride in this way?

The rest of this paper

8 more questions

Q2Equilibria11M
Q3Halogen Compounds10M
Q4Equilibria · Reaction Kinetics11M
Q5Halogen Compounds · Carboxylic Acids and Derivatives · Hydrocarbons · Introduction to A Level Organic Chemistry12M
Q6Organic Synthesis · Hydrocarbons · Introduction to A Level Organic Chemistry · Carboxylic Acids and Derivatives14M
Q7Reaction Kinetics10M
Q8Analytical Techniques10M
Q9Polymerisation10M

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