Nitrogen & Sulfur (Cambridge (CIE) AS Chemistry)

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]

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

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]

N₂O₅ is a rare and unstable oxide of nitrogen.

State the systematic name of N₂O₅.

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

What is meant by the following terms?

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

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

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

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

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 E_a values.

Fig. 1.1

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]

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 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]

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]

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

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

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

[2]

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

Give the equation for this reaction.

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]

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 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]

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.

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

[1]

ii) Write an equation for this process.

[1]

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.

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

SO₂ (g) + 1⁄2 O₂ (g) 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)  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]

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]

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

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]

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]

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]

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

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