(a)

(i)

Explain the lack of reactivity of nitrogen gas, $\mathrm{N}_{2}(\mathrm{~g})$ .

[ 2 ]

[Maximum number: 2]

In the Periodic Table, the p block contains elements whose outer electrons are found in the p subshell.

(a)

Sulfur-containing compounds, such as $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{SH}$ , are found in fossil fuels, and produce $\mathrm{SO}_{2}$ when they are burned.

[ 2 ]

(i)

State why the presence of $\mathrm{SO}_{2}$ in the atmosphere has environmental consequences. Describe one of the consequences on the environment.

[ 2 ]

[Maximum number: 8]

Nitrogen, $\mathrm{N}_{2}$ , is the most abundant gas in the Earth's atmosphere and is very unreactive.

(a)

State why $\mathrm{N}_{2}$ is very unreactive.

[ 1 ]

(b)

Magnesium and lithium both form nitrides with $\mathrm{N}_{2}$ . These compounds both contain the $\mathrm{N}^{3-}$ ion.

[ 2 ]

(i)

Write an equation for the reaction of magnesium with $\mathrm{N}_{2}$ to form magnesium nitride.

[ 1 ]

(ii)

Solid lithium nitride, $\mathrm{Li}_{3} \mathrm{~N}$ , reacts with water according to the following equation.

\mathrm{Li}_{3} \mathrm{~N}(\mathrm{~s})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 3 \mathrm{LiOH}(\mathrm{aq})+\mathrm{NH}_{3}(\mathrm{aq})

State one observation you would make during this reaction.

[ 1 ]

(c)

(i)

State the industrial importance of ammonia.

[ 1 ]

(ii)

One method of producing $\mathrm{NH}_{3}$ is by heating ammonium chloride, $\mathrm{NH}_{4} \mathrm{Cl}$ , with CaO .

2 \mathrm{NH}_{4} \mathrm{Cl}+\mathrm{CaO} \rightarrow 2 \mathrm{NH}_{3}+\mathrm{CaCl}_{2}+\mathrm{H}_{2} \mathrm{O}

Explain why the reaction of $\mathrm{NH}_{4} \mathrm{Cl}$ with CaO produces ammonia.

[ 2 ]

(d)

Three oxides of nitrogen, $\mathrm{NO}, \mathrm{NO}_{2}$ and $\mathrm{N}_{2} \mathrm{O}$ , can be formed under different conditions.

[ 2 ]

(i)

$\quad \mathrm{NO}_{2}$ can be formed by different chemical reactions.

Write equations for the formation of $\mathrm{NO}_{2}$ by:
- the reaction of $\mathrm{N}_{2}$ with $\mathrm{O}_{2}$
- the thermal decomposition of magnesium nitrate.

[ 2 ]

[Maximum number: 4]

Oxides are compounds which usually contain oxygen combined with one other element.
Oxides are classified as follows.
acidic alkaline amphoteric basic

(a)

Sulfur dioxide is present in small, but significant, amounts in the Earth's atmosphere.

[ 3 ]

(i)

State one way by which sulfur dioxide enters the atmosphere.

(ii)

Give the formula of another sulfur compound which is formed in the atmosphere from sulfur dioxide.

(iii)

What are the environmental consequences of the compound you have identified in (ii)?

[ 3 ]

(b)

Sulfur dioxide is used as a food preservative. What property of sulfur dioxide enables it to act in this way?

[ 1 ]

[Maximum number: 4]

Hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4}$ , can be used as a rocket fuel and is stored as a liquid. It reacts exothermically with oxygen to give only gaseous products.

The enthalpy change of a reaction such as that between hydrazine and oxygen may be calculated by using standard enthalpy changes of formation.

(a)

Hydrazine reacts with oxygen according to the following equation.

\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{N}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

[ 4 ]

(i)

Suggest why using hydrazine as a rocket fuel could be regarded as being ‘environmentally friendly’.

[ 4 ]

[Maximum number: 1]

Sulfides are compounds that contain sulfur but not oxygen.

(a)

The compound $\mathrm{As}_{2} \mathrm{~S}_{3}$ is a common mineral.

When $\mathrm{As}_{2} \mathrm{~S}_{3}$ is heated strongly in air, it forms a mixture of products, as shown.

2 \mathrm{As}_{2} \mathrm{~S}_{3}(\mathrm{~s})+9 \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{As}_{4} \mathrm{O}_{6}(\mathrm{~s})+6 \mathrm{SO}_{2}(\mathrm{~g})

[ 1 ]

(i)

State the environmental consequences of releasing $\mathrm{SO}_{2}(\mathrm{~g})$ into the atmosphere.

[ 1 ]

(a)

State one natural and one man-made occurrence of oxides of nitrogen.

[ 1 ]

(a)

(i)

State a major source of atmospheric sulfur dioxide.

[ 1 ]

(ii)

State one environmental consequence of atmospheric sulfur dioxide.

[ 1 ]

[Maximum number: 14]

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, $\mathrm{N}_{2}$ , is so unreactive.

Despite the apparent lack of reactivity of $\mathrm{N}_{2}$ , 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, $\mathrm{Li}_{3} \mathrm{~N}$ . Magnesium produces magnesium nitride, $\mathrm{Mg}_{3} \mathrm{~N}_{2}$ , as well as magnesium oxide, when heated in air.

[ 1 ]

(b)

Lithium reacts readily with nitrogen, and because of this $\mathrm{Li}_{3} \mathrm{~N}$ has been considered as a possible intermediate in the 'fixing' of nitrogen to make ammonia-based fertilisers.

[ 3 ]

(i)

Construct an equation for the reaction between $\mathrm{Li}_{3} \mathrm{~N}$ and $\mathrm{H}_{2} \mathrm{O}$ , and hence identify compound A.

[ 3 ]

(c)

Another possible advantage of $\mathrm{Li}_{3} \mathrm{~N}$ is that it contains a large percentage by mass of nitrogen. Another fertiliser that contains a large percentage by mass of nitrogen is urea, $\mathrm{NH}_{2} \mathrm{CONH}_{2}$ .

[ 10 ]

(i)

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

[ 5 ]

(ii)

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?

[ 5 ]

(a)

(i)

When $\mathrm{NO}_{2}$ reacts with water, nitrogen undergoes a disproportionation reaction in which one nitrogen atom decreases its oxidation number by 1 and another nitrogen atom increases its oxidation number by 1 . A mixture of two acids results. Suggest an equation for the reaction between $\mathrm{NO}_{2}$ and water.