9.6 Nitrogen and Sulphur Learning outcomes: Candidates should be able to: (a)Explain the lack of reactivity of nitrogen (b)Describe: (i)The formation and.

9.6 Nitrogen and Sulphur

Learning outcomes:

Candidates should be able to:

(a) Explain the lack of reactivity of nitrogen

(b) Describe:(i) The formation and structure of the ammonium ion(ii) The displacement of ammonia from its salts

(c) describe the Haber process for the manufacture of ammonia from its elements, giving essential operating conditions, and interpret theseconditions (qualitatively) in terms of the principles of kinetics and equilibria

(d) Understand the industrial importance of ammonia and nitrogen compoundsderived from ammonia

(e) Understand the environmental consequences of the controlled use of nitratefertilisers

(f) Understand and explain the occurrence and catalytic removal of oxides of nitrogen

(g) Explain why atmospheric oxides of nitrogen are pollutants, including theircatalytic role in the oxidation of atmospheric sulphur dioxide

(h) Describe the formation of atmospheric sulphur dioxide from the combustion of sulphur contaminated carbonaceous fuels

(i) State the role of sulphur dioxide in the formation of acid-rain and describe the main environmental consequences of acid-rain

(j) State the main details of the Contact process for sulphuric acid production

(k) Understand the industrial importance of sulphuric acid

(l) Describe the use of sulphur dioxide in food preservation

(a) Explain the lack of reactivity of nitrogen:

Group V

N::N

Nitrogen is a gas making up approximately78% of the atmosphere with a triple bond energy of 945 KJmol-1 hence explaining the lack of reactivity compared to other non-metals

It does react with the s-block metals, e.g.

3Mg(s) + N2(g) Mg3N2(s)Magnesium nitride

This results in a large activation energy, Ea

(b) Describe:The formation and structure of the ammonium ionThe displacement of ammonia from its salts

Ammonia, is produced commercially by the Haber Process.

N2(g) + 3H2(g) 2NH3(g) H = -92 KJmol-1

It can be acidified to give the ammonium ion:

NH3(aq) + H+(aq) NH4+(aq)

Ammonia is alkaline (a weak base) in aqueous solution and a typical reaction would be using dilute hydrochloric acid:

NH3(aq) + HCl(aq) NH4+(aq) + Cl-(aq)

Ammonia is clearly a base as it is a proton acceptor according to the Bronsted-Lowry definition of acids and bases.

Structure of the ammonium ion

Ammonia dissociates in water to a small extent (1%)

NH3(aq) + H20(l) NH4+(aq) + OH-(aq)

Can you remember the conjugate pairs (of acids and bases)?

It has a tetrahedral shape similar to methane (CH4)

In the gas phase, ammonia gas can react with hydrogen chloride:

NH3(g) + HCl(g) NH4Cl(s)

NH3(g) HCl(g)

cotton wool soaked cotton wool soakedin conc. ammonia in conc. HCl(aq)

Displacement of ammonia from its salts

If we add sodium hydroxide to ammonium chloride, the characteristic smell of ammonia is produced:

NaOH(aq) + NH4Cl(aq) NH3(aq) + NaCl(aq) + H2O(l)

The same is also true of organic amine salts:

NaOH(aq) + CH3CH2NH3Cl(aq) CH3CH2NH2(aq) + NaCl(aq) + H2O(l)

The group I metal hydroxide is clearly the stronger base!

(c) Describe the Haber process for the manufacture of ammonia from its elements, giving essential operating conditions, and interpret theseconditions (qualitatively) in terms of the principles of kinetics and equilibria

Ammonia, NH3, is produced commercially by the Haber Process.

N2(g) + 3H2(g) 2NH3(g) H = -92 KJmol-1Fe

460 oC200 atm

Haber Process

N2(g) + 3H2(g) 2NH3(g)Iron catalyst

Operating Conditions

• N2 and H2 are pumped into a chamber.

• The pre-heated gases are passed through a heating coil to the catalyst bed.

• The catalyst bed is kept at 460 - 550 C under high pressure.

• The product gas stream (containing N2, H2 and NH3) is passed over a cooler to a refrigeration unit.

• In the refrigeration unit, ammonia liquefies, but not N2 or H2.

Haber ProcessHaber Process (contd.) (contd.)

1. Kinetics

A catalyst (iron) is used to speed up the rate of reaction and to lower the high activation energy in breaking the N2 triple bond. However, if the temperature is too high, it begins to get destroyed and must be changed more regularly.

Haber ProcessHaber Process (contd.) (contd.)

In the Haber Process for the production of ammonia, based on the reversible reaction:

it is observed that:• As the total pressure increases, the amount of ammonia

present at equilibrium increases.• As the temperature decreases, the amount of ammonia at

equilibrium increases.

Effect of temperature and pressure Effect of temperature and pressure on Haber Processon Haber Process

N2(g) + 3H2(g) 2NH3(g)

An example:

Haber Process

N2(g) + 3H2(g) 2NH3(g)

(d) Understand the industrial importance of ammonia and nitrogen compounds derived from ammonia

Most of the ammonia produced is used to make nitric acid and fertilizers.

1. Ammonia and oxygen are passed over a hot platinum catalyst:

About 95% of the ammonia is converted into nitrogen monoxide

2. The gases are cooled and mixed with more air. Then under pressure,they are passed up a tower that has water trickling down it and nitric acidis produced:

4NO(g) + 3O2(g) + 2H2O(l) 4HNO3(aq)

Overall:NH3(g) + 2O2(g) HNO3(aq) + H2O(l)

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(l) H = -909 KJmol-1

Conditions: 1100K and 4-10 atm. pressure

Pt

The conversion of NO into nitric acid actually occurs in three stages:

a. 2NO(g) + O2(g) 2NO2(g) H = -115 KJmol-1

b. 2NO2(g) N2O4(g) H = -58 KJmol-1

c. 3N2O4(g) + 2H2O(l) 4HNO3(aq) + 2NO(g)

Nitric acid is used to make fertilizers, explosives and the polyamide, Nylon

Commercial uses of nitric acid:

Fertilizers 化肥

Ammonium salts are used as fertilizers because they contain nitrogen in a formthat plants can use. The fertilizer Nitram is ammonium nitrate and is made froma solution of ammonia in water and nitric acid in an acid-base reaction:

NH3(aq) + HNO3(aq) NH4NO3(aq)

Similar neutralization reactions with phosphoric(V) and sulphuric acids:

2NH3(aq) + H2SO4(aq) (NH4)2SO4(aq)

(e) Understand the environmental consequences of the controlled use of nitrate fertilisers

Ammonium nitrate is a good fertilizer: it contains 35% by mass ofnitrogen all of which is available to plants as it dissolves easily.

However, some nitrate ions are washed into rivers and streams whichencourages rapid growth of algae. However, when algae die they aredecomposed by bacteria and this uses up oxygen dissolved in water.

The fish begin to suffocate and die from a lack of oxygen.

Nitrates also get into drinking water as they are not purified and athigh levels can cause problems for small babies by affecting haemoglobin(used in respiration and transport of O2 in the blood).

In today’s lesson…..

(d) Understand the industrial importance nitrogen compounds derived from ammonia (revision from yesterday)

(e) Understand the environmental consequences of the controlled use of nitrate fertilisers (revision from yesterday)

(f) Understand and explain the occurrence and catalytic removal of oxides of nitrogen (new)

(g) Explain why atmospheric oxides of nitrogen are pollutants, including their catalytic role in the oxidation of atmospheric sulphur dioxide (new)

We can test some of our knowledge in a past-paper style question on catalytic removal of NO in car engines

We can test some of our knowledge in a past-paper style question on manufactureof nitric acid

(d) Understand the industrial importance of ammonia and nitrogen compounds derived from ammonia

Most of the ammonia produced is used to make nitric acid and fertilizers.

1. Ammonia and oxygen are passed over a hot platinum catalyst:

About 95% of the ammonia is converted into nitrogen monoxide

2. The gases are cooled and mixed with more air. Then under pressure,they are passed up a tower that has water trickling down it and nitric acidis produced:

4NO(g) + 3O2(g) + 2H2O(l) 4HNO3(aq)

Overall:NH3(g) + 2O2(g) HNO3(aq) + H2O(l)

4NH3(g) + 5O2(g) 4NO(g) + 6H2O(l) H = -909 KJmol-1

Conditions: 1100K and 4-10 atm. pressure

Pt

The conversion of NO into nitric acid actually occurs in three stages:

a. 2NO(g) + O2(g) 2NO2(g) H = -115 KJmol-1

b. 2NO2(g) N2O4(g) H = -58 KJmol-1

c. 3N2O4(g) + 2H2O(l) 4HNO3(aq) + 2NO(g)

Concentrated nitric acid (66%) is a strong acid:

HNO3(aq) H+(aq) + NO3-(aq)

It is also an oxidising agent and reacts with most metals to form nitratesand nitrogen oxides:

Cu(s) + 2HNO3(aq) Cu(NO3)2(aq) + H2O(l) + NO2(g)

Properties of nitric(v) acid

Nitric acid is used to make fertilizers, explosives and the polyamide, Nylon

Commercial uses of nitric acid:

Fertilisers 化肥

Ammonium salts are used as fertilisers because they contain nitrogen in a formthat plants can use. The fertiliser Nitram is ammonium nitrate and is made froma solution of ammonia in water and nitric acid in an acid-base reaction:

NH3(aq) + HNO3(aq) NH4NO3(aq)

Similar neutralization reactions with phosphoric(V) and sulphuric acids:

2NH3(aq) + H2SO4(aq) (NH4)2SO4(aq)


Ammonium nitrate is a good fertiliser: it contains 35% by mass ofnitrogen all of which is available to plants as it dissolves easily.

However, some nitrate ions are washed into rivers and streams whichencourages rapid growth of algae 藻类 . However, when algae die they are decomposed by bacteria and this uses up oxygen dissolved in water.

The fish begin to suffocate and die from a lack of oxygen.

Nitrates also get into drinking water as they are not purified and athigh levels can cause problems for small babies by affecting haemoglobin血红蛋白 (used in respiration and transport of O2 in the blood).


The combustion engines in cars produce a number of pollutinggases, including a small amount of NOx:

Carbon monoxide, which is poisonous.

Nitrogen oxides (NO, NO2 and N2O4) which cause acid rain andhelp to destroy the ozone (O3) layer in the upper atmosphere.

Unburnt hydrocarbons may cause cancer.

Unburnt hydrocarbons react with nitrogen oxides in sunlight to form smogs (containing ozone) at low levels in the atmosphere, especially in large hot cities.

N2(g)+ O2(g) 2NO(g) : the excess heat in an engine produces NO

Catalytic removal of nitrogen oxides

These poisonous gases may be removed by the use of a catalytic converterIn car exhaust systems. It is honeycomb in shape to provide a largesurface area and is coated with platinum and rhodium metal catalysts:

Carbon monoxide + nitrogen oxide nitrogen + carbon dioxide

Hydrocarbons + nitrogen oxide nitrogen + carbon dioxide + water

Pt or Rh1100K

NO-CO N2 CO2ON CO2

CO

Inside a catalytic converter

(g) Explain why atmospheric oxides of nitrogen are pollutants, including their catalytic role in the oxidation of atmospheric sulphur dioxide


In more detail:

Nitric oxide (NO) reacts with oxygen to produce nitrogen dioxide:

2NO(g) + O2(g) 2NO2(g)

NO2 dissolves in rain to form a mixture of nitric(v) and nitric(III) acids:

2NO2(g) + H2O(l) HNO3(aq) + HNO2(aq)What type of redox reaction is this? disproportionation

These acids are help to form acid rain; they are corrosive and damage construction materials that are attacked by acids especially marble ( 大理石 ), so some ancient monuments lose their features.

NO and NO2 have a catalytic role in the conversion of atmospheric sulphur dioxide to sulphur trioxide:

2NO(g) + O2(g) 2NO2(g)

SO2(g) + NO2(g) SO3(g) + NO(g)

Did you know?

The explosive TNT uses fumingnitric acid (98%) in its manufacture

Trinitrotoluene

Sulphur trioxide dissolves in rain water to form sulphuric acid and aquatic life may be destroyed in lakes and it also destroys limestone and marble.

To summarize…..

(d) Understand the industrial importance nitrogen compounds derived from ammonia



(g) Explain why atmospheric oxides of nitrogen are pollutants, including theircatalytic role in the oxidation of atmospheric sulphur dioxide

In tomorrow’s lesson we will study sulphur chemistry, in particularthe contact process for formation of SO3 and H2SO4


(f) Understand and explain the occurrence and catalytic removal of oxides of nitrogen (revision)

(g) Explain why atmospheric oxides of nitrogen are pollutants, including their catalytic role in the oxidation of atmospheric sulphur dioxide (rev.)

(h) Describe the formation of atmospheric sulphur dioxide from the combustion of sulphur contaminated carbonaceous fuels (new)

(i) State the role of sulphur dioxide in the formation of acid-rain and describe the main environmental consequences of acid-rain (new)

(j) State the main details of the contact process for sulphuric acid production (also see equilibria hand-out) (new)

We will test our knowledge using an exam style question to check our revisionof nitrogen chemistry, nitric oxides and catalytic role with SO2


The combustion engines in cars produce a number of pollutinggases, including a small amount of NOx:

Carbon monoxide, which is poisonous.


Unburnt hydrocarbons may cause cancer.

Unburnt hydrocarbons react with nitrogen oxides in sunlight to form smogs (containing ozone) at low levels in the atmosphere, especially in large hot cities.

N2(g)+ O2(g) 2NO(g) : the excess heat in an engine produces NO

Catalytic removal of nitrogen oxides

These poisonous gases may be removed by the use of a catalytic converterIn car exhaust systems. It is honeycomb in shape to provide a largesurface area and is coated with platinum and rhodium metal catalysts:

Carbon monoxide + nitrogen oxide nitrogen + carbon dioxide

Hydrocarbons + nitrogen oxide nitrogen + carbon dioxide + water

Pt or Rh1100K

NO-CO N2 CO2ON CO2

CO

Inside a catalytic converter

(g) Explain why atmospheric oxides of nitrogen are pollutants, including their catalytic role in the oxidation of atmospheric sulphur dioxide


In more detail:

Nitric oxide (NO) reacts with oxygen to produce nitrogen dioxide:

2NO(g) + O2(g) 2NO2(g)

NO2 dissolves in rain to form a mixture of nitric(v) and nitric(III) acids:

2NO2(g) + H2O(l) HNO3(aq) + HNO2(aq)What type of redox reaction is this? disproportionation

These acids are help to form acid rain; they are corrosive and damage construction materials that are attacked by acids especially marble ( 大理石 ), so some ancient monuments lose their features.

NO and NO2 have a catalytic role in the conversion of atmospheric sulphur dioxide to sulphur trioxide:

2NO(g) + O2(g) 2NO2(g)

SO2(g) + NO2(g) SO3(g) + NO(g)

Did you know?

The explosive TNT uses fumingnitric acid (98%) in its manufacture

Trinitrotoluene

Sulphur trioxide dissolves in rain water to form sulphuric acid and aquatic life may be destroyed in lakes and it also destroys limestone and marble.

Sulphur (Group VI)


Coal, an impure form of graphite is used as a fossil fuel and is still used in boilers to heat water. It was more popular in England more than onehundred years ago in the Victorian Days.

However, small amounts of sulphur are oxidized to corrosive and foulsmelling sulphur dioxide, which contributes to pollution:

S(s) + O2(g) SO2(g)

structure of SO2

SO2(g) + H2O(l) H2SO3(aq)


Sulphur dioxide released into the atmosphere dissolves in rain and forms sulphuric (IV) acid more commonly known as sulphurous acid; some SO2 comes from natural sources such as volcanoes, where hot sulphur reacts with O2:

This is corrosive and damages construction materials that are attacked by acidsespecially marble ( 大理石 ), so some ancient monuments lose their features.

Acid-rain also effects forests and kills some plants, algae and fish in natural lakes,and the more acid-rain produced the worse the effect.

formation of acid-rain

(j) State the main details of the contact process for sulphuric acid production (see equilibria hand-out)

Sulphuric acid, H2SO4 is produced from sulphur, water and oxygen by theContact process.

1. Sulphur is burnt to sulphur dioxide:

S(s) + O2(g) SO2(g)

2. Sulphur dioxide is converted to suphur trioxide by reaction with moreoxygen using a catalyst of vanadium(v) oxide:

2SO2(g) + O2(g) 2SO3(g) H = -197 KJmol-1

V2O5

710K

Effect of temperature and pressure Effect of temperature and pressure on the contact processon the contact process

Le Chateliers principle predicts that for the exothermic forward reaction cooling will produce the maximum yield (95%): the equilibrium is shifted to the right. The SO3 is removed by dissolving it in conc. H2SO4. However, the rate of reaction to reach equilibrium increases with temperature increase.

The yield can be increased to 99.5% by passing the remaining reactant gasesover the hot catalyst (on a fourth catalyst bed).

Although increasing the pressure will shift the equilbrium to the rightas fewer gas molecules are produced, there are more operational energy costs and in practice the process is run at near atmospheric pressure (only anextra 0.5% conversion achieved!)

2SO2(g) + O2(g) 2SO3(g) H = 197 KJmol-1V2O5

710K

Temperature

Pressure

A flow diagram

Purifier and drier

Air

Heatexchanger

Catalyticchamber

Absorptiontower

Purifier and drier

Sulphurburner

Air

H2SO4 store

water

98% H2SO4c.H2SO4

oleum

drySO2+air

SO3

3. Formation of H2SO4

The absorbed SO3 reacts with the water in sulphuric acid to form moresulphuric acid so that the acid becomes even more concentrated:

SO3(g) + H2O(l) H2SO4(l)

SO3(g) + H2SO4(l) H2S2O7(l)

Properties of H2SO4: Viscous liquid with hydrogen bonding

1. Strong acid:

H2SO4(l) H+(aq) + HSO4-(aq)

HSO4-(aq) H+(aq) + SO4

2-(aq)

2. Dehydrating agent:

CuSO4.5H2O(s) CuSO4(s) + 5H2O(l)

3. Oxidizing agent

8HI(g) + H2SO4(l) 4H2O(l) + H2S(g) + 4I2(s)

H2SO4

H2O

H2S2O7(l) + H2O(l) 2H2SO4(l)

oleum

Practice questions

Sulphuric acid is manufactured from sulphur in four stages

S(s) + O2(g) SO2(g)

2SO2(g) + O2(g) 2SO3(g)


H2S2O7(l) + H2O(l) 2H2SO4(l)

(a) Give the oxidation number of sulphur in each species.

(b) Which two steps are redox reactions?

0 +IV

+VI

+VI +VI

√

√

To summarize what we have learnt today…..



(j) State the main details of the Contact process for sulphuric acid production

Tomorrow we will understand:



Revise nitrogen and sulphur


(h) Describe the formation of atmospheric sulphur dioxide from the combustion of sulphur contaminated carbonaceous fuels (rev.)

(i) State the role of sulphur dioxide in the formation of acid-rain and describe the main environmental consequences of acid-rain (rev.)

(j) State the main details of the contact process for sulphuric acid production (also see equilibria hand-out) (rev.)

(k) Understand the industrial importance of sulphuric acid(new)

(l) Describe the use of sulphur dioxide in food preservation (new)

Keywords: SO2, acid-rain, SO3, Contact Process, H2SO4, SO2-food preservation

Sulphur (Group VI)


Coal, an impure form of graphite is used as a fossil fuel and is still used in boilers to heat water. It was more popular in England more than onehundred years ago in the Victorian Days.

However, small amounts of sulphur are oxidized to corrosive and foulsmelling sulphur dioxide, which contributes to pollution:

S(s) + O2(g) SO2(g)

structure of SO2

SO2(g) + H2O(l) H2SO3(aq)


Sulphur dioxide released into the atmosphere dissolves in rain and forms sulphuric (IV) acid more commonly known as sulphurous acid; some SO2 comes from natural sources such as volcanoes, where hot sulphur reacts with O2:

This is corrosive and damages construction materials that are attacked by acidsespecially marble ( 大理石 ), so some ancient monuments lose their features.

Acid-rain also effects forests and kills some plants, algae and fish in natural lakes,and the more acid-rain produced the worse the effect.

formation of acid-rain

(j) State the main details of the contact process for sulphuric acid production (see equilibria hand-out)

Sulphuric acid, H2SO4 is produced from sulphur, water and oxygen by theContact process.

1. Sulphur is burnt to sulphur dioxide:

S(s) + O2(g) SO2(g)

2. Sulphur dioxide is converted to suphur trioxide by reaction with moreoxygen using a catalyst of vanadium(v) oxide:

2SO2(g) + O2(g) 2SO3(g) H = -197 KJmol-1

V2O5

710K

Effect of temperature and pressure Effect of temperature and pressure on the contact processon the contact process

Le Chateliers principle predicts that for the exothermic forward reaction cooling will produce the maximum yield (95%): the equilibrium is shifted to the right. The SO3 is removed by dissolving it in conc. H2SO4. However, the rate of reaction to reach equilibrium increases with temperature increase.

The yield can be increased to 99.5% by passing the remaining reactant gasesover the hot catalyst (on a fourth catalyst bed).

Although increasing the pressure will shift the equilbrium to the rightas fewer gas molecules are produced, there are more operational energy costs and in practice the process is run at near atmospheric pressure (only anextra 0.5% conversion achieved!)

2SO2(g) + O2(g) 2SO3(g) H = 197 KJmol-1V2O5

710K

Temperature

Pressure

A flow diagram

Purifier and drier

Air

Heatexchanger

Catalyticchamber

Absorptiontower

Purifier and drier

Sulphurburner

Air

H2SO4 store

water

98% H2SO4c.H2SO4

oleum

drySO2+air

SO3

3. Formation of H2SO4

The absorbed SO3 reacts with the water in sulphuric acid to form moresulphuric acid so that the acid becomes even more concentrated:

SO3(g) + H2O(l) H2SO4(l)


Properties of H2SO4: Viscous liquid with hydrogen bonding

1. Strong acid:

H2SO4(l) H+(aq) + HSO4-(aq)

HSO4-(aq) H+(aq) + SO4

2-(aq)

2. Dehydrating agent:

CuSO4.5H2O(s) CuSO4(s) + 5H2O(l)

3. Oxidizing agent

8HI(g) + H2SO4(l) 4H2O(l) + H2S(g) + 4I2(s)

H2SO4

H2O

H2S2O7(l) + H2O(l) 2H2SO4(l)

oleum


Sulphuric acid is an important industrially produced chemical.Its main uses are:-

Paints and pigments 染料涂料

Fertilisers 化肥

Fibres and dyes 县委染料

Soaps and detergents 香皂洗涤剂

Cleaning metals 除锈剂

Chemicals and plastics 化学品塑料

Tanning leather 皮革

(l) Describe the use of sulphur dioxide in food preservation (new)

Sulphur dioxide is poisonous to bacteria and is used as a food preservative(E220 on food labels in the U.K.) especially in the preparation of fruit juicesand soft drinks and to kill bacteria in wine-making as it is slightly soluble in water.

SO2(g) + H2O(l) H2SO3(aq) H+(aq) + HSO3-(aq)

Sodium metabisulphite (Na2S2O5) is another preservative (E222) and liberatesSO2(g) upon acidification.

In today’s lesson we learnt:



9.6 Nitrogen and Sulphur Learning outcomes: Candidates should be able to: (a)Explain the lack of reactivity of nitrogen (b)Describe: (i)The formation and.

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