Nitrogen and Sulfur (Cambridge (CIE) A Level Chemistry): Exam Questions

Nitrogen and oxygen react together under conditions of high temperature to give oxides of nitrogen.

i) Draw a dot-and-cross diagram to show the arrangement of outer-shell electrons in a molecule of nitrogen.

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ii) Explain why high temperatures are required for oxides of nitrogen to form.

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i) Construct an equation for a possible reaction between nitrogen and oxygen.

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ii) The bond enthalpy of the N≡N triple bond in N₂ is +944 kJ mol⁻¹.

Suggest the bond enthalpy of the O=O bond in oxygen. Give a reason for your answer.

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i) Identify one natural process and one man-made process in which nitrogen and oxygen react together to form oxides of nitrogen.

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ii) State two environmental effects of the presence of nitrogen oxides in the atmosphere.

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State the systematic name of N₂O₅.

Nitrogen oxides in the atmosphere act as homogeneous catalysts in the formation of acid rain.

Explain what is meant by the term homogeneous catalyst.

Identify one man-made source of oxides of nitrogen in the atmosphere. Explain how they are formed.

Construct equations to show the role played by nitrogen oxides in the formation of acid rain.

On Fig. 1.1, sketch a fully labelled reaction pathway diagram for an exothermic reaction in the presence and absence of a catalyst.

Label the enthalpy change of reaction, ΔH, and the activation energy, E_a, for both pathways.

Fig. 1.1

Ammonia, NH₃, is synthesised from its elements in the Haber process.

i) Construct an equation for this process.

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ii) State the three usual operating conditions of the Haber process.

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Ammonia can act as a Brønsted–Lowry base.

Explain why.

1.50 dm³ of ammonia gas were dissolved in water to form 300 cm³ of aqueous alkali at room conditions.

i) Calculate the amount, in mol, of NH₃(g) dissolved.

Show your working.

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ii) Construct an equation for the neutralisation of aqueous ammonia by dilute sulfuric acid.

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iii) Calculate the volume of 0.80 mol dm^–3 sulfuric acid that is required to neutralise the 300 cm³ of aqueous ammonia.

Show your working.

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i) Draw a three-dimensional diagram of each species below to show its shape. Clearly show the bond angles.

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ii) State the name of the shape of an ammonia molecule and an ammonium ion.

Ammonia molecule ................................................................................

Ammonium ion .........................................................................................

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Ammonia gas can also be prepared by heating a mixture of ammonium chloride and calcium hydroxide.

Construct an equation for this reaction.

The high temperatures reached in an internal combustion engine cause nitrogen and oxygen from the air to react, forming nitrogen monoxide.

i) Construct an equation for this reaction.

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ii) Deduce the oxidation number of nitrogen in N₂ and NO to show that nitrogen is oxidised in this reaction.

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iii) Nitrogen monoxide reacts further with oxygen to form nitrogen dioxide.

Construct an equation for this reaction.

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Nitrogen oxides play a role in the formation of photochemical smog. Explain how.

The brown haze associated with photochemical smog is typically worse in cities in the afternoons of hot sunny days.

Suggest why.

Catalytic converters are fitted to exhaust systems to reduce the pollutants emitted by car engines. Nitrogen monoxide, NO, and carbon monoxide, CO, are removed in a catalytic converter, forming nitrogen and carbon dioxide.

i) Construct an equation for the removal of NO and CO.

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ii) Identify the reducing agent in this reaction. Explain your answer using changes in oxidation numbers.

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Nitrogen dioxide, NO₂, is a pollutant gas produced in the combustion of fuels in motor vehicles and power stations.

Construct an equation for the formation of NO₂ from its elements.

i) State how NO₂ is removed from the exhaust gases of motor vehicles.

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ii) Construct an equation for this process.

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Suggest whether the production of the pollutant NO₂ in motor vehicles would be reduced if fossil fuels were replaced by hydrogen as a fuel for combustion. Explain your answer.

In the atmosphere, NO₂ acts as a homogeneous catalyst for the oxidation of SO₂ to SO₃.

SO₂ (g) + 1⁄2 O₂ (g) SO₃ (g)

i) State one environmental consequence of the formation of SO₃ in the atmosphere.

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The oxidation takes place in two steps. The initial reaction is between NO₂ and SO₂.

reaction 1 NO₂ (g) + SO₂ (g) NO (g) + SO₃ (g) ΔH = −168 kJ mol⁻¹

ii) Construct an equation to show how the NO₂ catalyst is regenerated in the second step.

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iii) The temperature of the atmosphere decreases with height from the ground.

Suggest how the position of the equilibrium in reaction 1 changes as height increases. Explain your answer.

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Ammonia gas can be prepared from ammonium chloride and calcium hydroxide.

i) Explain how ammonia can be prepared from these reagents.

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ii) Describe a test and the expected observation to confirm the presence of ammonia gas.

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Explain, using the Brønsted–Lowry theory, why the reaction between ammonium chloride and calcium hydroxide is an example of an acid-base reaction.

i) Draw a dot-and-cross diagram to show the bonding in an ammonium ion.

Show outer-shell electrons only.

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ii) All four N-H bonds in the ammonium ion are equal in length. Explain why.

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Nitrogen gas, N₂, is very unreactive.

i) Explain the lack of reactivity of the nitrogen molecule.

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ii) State the number of σ (sigma) and π (pi) bonds in a nitrogen molecule.

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In an internal combustion engine, nitrogen reacts with oxygen to form nitrogen monoxide, NO. In the atmosphere, NO is further oxidised to nitrogen dioxide, NO₂. Nitrogen dioxide then reacts with oxygen and water in the atmosphere to form dilute nitric acid, HNO₃.

i) Construct equations for these three reactions. Include state symbols.

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ii) Identify the change in oxidation number of nitrogen in each reaction, and state whether nitrogen is oxidised or reduced.

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A car travelled one kilometre and released 0.23 g of an oxide of nitrogen, N~x_Oy~, which occupies 120 cm³ at room conditions.

Calculate the values of x and y. Show your working.