CIE AS Chemistry

Topic Questions

ASChemistryCIETopic Questions2. Inorganic Chemistry2.4 Nitrogen & Sulfur

Syllabus Edition

First teaching 2020

Last exams 2024

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2.4 Nitrogen & Sulfur

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1a2 marks

Extreme conditions are required to synthesise ammonia from nitrogen in the Haber process due to the lack of reactivity of the nitrogen molecule. 

Give two reasons for the lack of reactivity of the nitrogen molecule, N2.

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1b5 marks

Under conditions of high temperature, nitrogen and oxygen react together to give oxides of nitrogen.

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

[1]

ii)
State two situations, one natural and one as a result of human activities, in which nitrogen and oxygen react together.

[2]

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

[2]

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1c1 mark
i)
State how nitrogen monoxide is removed from the exhaust gases of motor vehicles.

[1]

ii)
Write an equation for this process.

[1]

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2a2 marks

Nitrogen oxides can react with substances in the air to make secondary pollutants.

One of these secondary pollutants is peroxyacetyl nitrate, commonly known as PAN.

i)
State the type of compounds that react with nitrogen oxides to form PAN.

[1]

ii)
PAN is one of the components found in photochemical smog. Explain why the term photochemical is used to describe smog.

[1]

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2b3 marks

One of the main reasons for reducing the amounts of oxides of nitrogen in the atmosphere is their contribution to the formation of acid rain.

i)
Write an equation for the formation of nitric acid from nitrogen dioxide, NO2, in the atmosphere.

[2]

ii)
State the role that nitrogen dioxide, NO2, plays in the oxidation of atmospheric sulfur dioxide, SO2, to form acid rain.

[1]

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2c1 mark

State the oxidation number of nitrogen in nitrogen monoxide, NO, and nitrogen dioxide, NO2.

oxidation number in NO  ............................................................
oxidation number in NO2 ............................................................

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3a3 marks

Ammonium sulfate is a fertiliser which is manufactured by the reaction between ammonia and sulfuric acid.

Ammonia is described as a weak base and sulfuric acid as a strong acid. By using an equation, explain clearly why ammonia can be described as a weak base.

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3b4 marks
i)
Write the equation for the neutralisation of aqueous ammonia by dilute sulfuric acid.

[1]

ii)
State the bond angles between N-H bonds in ammonia and the ammonium ion. Explain any differences

[3]

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3c3 marks

Ammonia can be displaced from an ammonium salt by an acid–base reaction. One such reaction is between ammonium chloride and calcium hydroxide.

i)
Write the equation for the reaction between ammonium chloride and calcium hydroxide.

[2]

ii)
Explain how the presence of ammonia gas can be confirmed.

[1]

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1a1 mark

The combustion of fuels in motor vehicles, trains, aeroplanes and power stations produces the pollutant gas NO2.

Write an equation to show how NO2 is formed in these situations.

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1b2 marks
i)
State how NO2 is removed from the exhaust gases of motor vehicles.
[1]
ii)
Write an equation for this process.
[1]

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1c1 mark

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

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1d4 marks

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

SO2 (g) + 1⁄2 O2 (g) rightwards arrow with NO subscript 2 on top SO3 (g)

i)
What is the environmental significance of this reaction?

[1]

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

reaction 1           NO2 (g) + SO2 (g) rightwards harpoon over leftwards harpoon NO (g) + SO3 (g)       ΔH = –168 kJ mol–1

ii)
Write an equation to show how the NO2 is regenerated in the second step of the oxidation.
[1]

iii)
The temperature of the atmosphere decreases with height. Explain how this will affect the position of the equilibrium in reaction 1.
[2]

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2a3 marks

This question is about ammonia.

i)
Explain how ammonia can be prepared from ammonium chloride and calcium hydroxide.

[2]

ii)
Explain how the presence of ammonia gas can be confirmed.

[1]

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2b2 marks

Explain why the reaction between ammonium chloride and calcium hydroxide is an example of an acid-base reaction.

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2c3 marks
i)
Draw a diagram of the ammonium ion showing all of the bonds within the molecule.

[2]

ii)
The N-H bonds in the ammonium ion have been found to be equal in length. Suggest what this means about the bonds or charge on the ion.

[1]

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3a3 marks

A molecule of nitrogen will only react with oxygen under extreme conditions due to the strong triple bond between nitrogen atoms.

i)
State another reason why the nitrogen molecule is so unreactive.

[1]

ii)
State the type of covalent bonds that exists between the two nitrogen atoms.

[2]

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3b6 marks

Despite the unreactivity of nitrogen, certain extreme conditions can trigger a series of reactions from which the nitrogen in the atmosphere is involved in the production of nitric acid, causing acid rain.

Step 1: The temperatures reached inside a combustion engine provide the high activation required to overcome the high bond enthalpy of nitrogen, allowing the formation of nitrogen(II) oxide
Step 2: Nitrogen(II) oxide further reacts to give nitrogen(IV) oxide
Step 3: Nitrogen(IV) oxide dissolves in water and reacts with more oxygen to form dilute nitric acid


i)
Write three equations to show each of these reactions. Include state symbols.

[3]

ii)
Identify the changes in oxidation number of nitrogen in each reaction and use this to state if nitrogen is oxidised or reduced in each reaction.

[3]

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3c
Sme Calculator3 marks

A car travelled one kilometre and released 0.23 g of an oxide of nitrogen, NxOy, which occupies 120 cm3.

Calculate the values of x and y.
(Assume 1 mol of gas molecules occupies 24.0 dm3).

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1a5 marks

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

i)
Draw the dot-and-cross diagram of a molecule of nitrogen.

[2]

ii)
Suggest and explain why high temperatures are required for oxides of nitrogen to form.

[3]

How did you do?

1b2 marks
i)
Write an equation for a possible reaction between nitrogen and oxygen.
 
[1]
 
ii)
The bond enthalpy of nitrogen is +1000 kJ mol-1.
 
Suggest the bond enthalpy of oxygen.
 
[1]
 
Possible bond enthalpy of oxygen ...................................... kJ mol-1

How did you do?

1c4 marks
i)
State two situations, one natural and one as a result of human activities, in which nitrogen and oxygen react together.

[2]

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

[2]

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1d1 mark

N2O5 is a rare and unstable oxide of nitrogen.

State the systematic name of N2O5.

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2a3 marks

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

What is meant by the following terms?

catalyst ......................................................................................

homogeneous ..........................................................................

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2b2 marks

State a major source of nitrogen oxides in the atmosphere, explaining how they are formed.

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2c3 marks

Use equations to describe the chemical role played by nitrogen oxides in the formation of acid rain.

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2d3 marks

Use the following axes in Fig. 1.1 to draw a fully labelled reaction pathway diagram showing the effect of a catalyst on an exothermic reaction.

Label the ∆H and Ea values.

2-4m-q2c-reaction-pathway-diagram

Fig. 1.1

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3a2 marks

Ammonia, NH3, is a colourless, pungent-smelling gas that has been known to man from the beginning of recorded time. Now ammonia is synthesised from its elements in the Haber process. 

i)
Write an equation for this process.

[1]

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

[1]

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3b2 marks

Ammonia can act as a Brønsted–Lowry base.

Explain why.

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3c
Sme Calculator4 marks

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

i)
Calculate how many moles of NH3 (g) were dissolved.
Show your working.

[1]

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

[1]

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.

[2]

How did you do?

3d6 marks
i)
In the boxes below, draw diagrams to show the shapes of an ammonia molecule and an ammonium ion.
Clearly show the bond angles on your diagrams.
[4]
   
Ammonia Ammonium ion

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

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

Ammonium ion .........................................................................................
[2]

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3e2 marks

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

Give the equation for this reaction.

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4a3 marks

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

i)
Give the equation for this reaction.

[1]

ii)
Show, using oxidation numbers, that nitrogen has been oxidised.

[1]

iii)
Nitrogen monoxide will react further with oxygen to form nitrogen dioxide.
Give the equation for this oxidation reaction.

[1]

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4b3 marks

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

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4c3 marks

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

Suggest why.

How did you do?

4d3 marks

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

i)
Give the balanced symbol equation for the removal of NO and CO.

[1]

ii)
State, using oxidation numbers, what is acting as a reducing agent in this reaction.

[2]

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