AMMONIA AND FERTILISERS
What is a reversible reaction?
How do we make fertilisers?
What are the benefits and drawbacks of using
fertilisers?
Name ____________________________
Class
__________
Date
__________
Teacher
____________________________
CHEM - ADDITIONAL BOOKLET 5
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AMMONIA AND FERTILISERS
Tick
You should:
Know that ammonia is made from atmospheric nitrogen
by the reversible reaction
Interpret given data to show how the yield of
product depends upon the conditions used in the
manufacture of ammonia
Know how nitrogenous fertilisers such as ammonium
sulphate and ammonium nitrate are obtained by
neutralising ammonia solution (ammonium hydroxide)
with sulphuric acid or nitric acid respectively.
Evaluate the advantages and disadvantages of using
nitrogenous fertilisers for individuals, communities and
the environment.
Identify the presence of an ammonium salt by
reaction with sodium hydroxide solution to produce
ammonia gas
Identify the alkaline gas ammonia by its action on
damp red litmus paper
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NITROGEN CHEMISTRY
INTRODUCTION
ABOUT NITROGEN

Nitrogen was discovered by chemist and
physician Daniel Rutherford in 1772.

Nitrogen compounds are found in foods,
organic materials, fertilisers, poisons,
and explosives.

Nitrogen, as a gas is colourless,
odorless, and generally considered an inert element.

As a liquid (boiling point = - 195.8oC), it is also colorless and
odorless, and is similar in appearance to water.
Watch the following clip showing a banana and apple being dipped into
liquid nitrogen. Click on picture.
Google Image Result for
http://www.ilpi.com/genchem/demo/liquidnitrogen/nitrogenintro.jpg
79% of the air around us is nitrogen. Living things need nitrogen to
make proteins, but they cannot get it directly from the air because
nitrogen gas is too stable to react inside an organism to make new
compounds.
OBTAINING NITROGEN FROM THE AIR- NITROGEN
FIXATION
Nitrogen must be changed into a more reactive form to allow plants
and animals to use it. Plants can take up and use nitrogen when it is in
the form of:
 Nitrates
 Ammonium salts.
Changing nitrogen into a more reactive substance is called nitrogen
fixation.
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Nitrogen fixation happens in three main ways:
1. The energy in a lightening bolt can split the nitrogen molecule in
the air allowing each nitrogen atom to react with oxygen to form
nitrogen oxides. These oxides are washed to the ground by the
rain where they form nitrates.
2. The Haber Process is used by industry to produce ammonia from
nitrogen. Ammonia is used to make fertiliser for farmers to feed
their crops.
3. Nitrogen-fixing bacteria found in the soil and in the root nodules
of leguminous plants fix nitrogen into a usable form.
Other ways in which nitrogen compounds are returned to the soil are by
excretion and egestion from animals or when plants and animals die
and decay.
THE HABER PROCESS
Nitrogen is the most common gas in the atmosphere. It can be
used to make ammonia when it is combined with hydrogen gas.
This is a REVERSIBLE reaction
–
we looked at reversible reactions in the
‘chemical reactions’ booklet. Remember the
blue
bottle
experiment?
Reversible
reactions go backwards and forwards.
HISTORY
The HABER PROCESS is a method of producing ammonia developed
in WWI. The Germans needed nitrogen for making their explosives.
When the Allies blocked off all trade routes going to and fron
Germany, they lost all source of sodium nitrate and potassium
nitrate, their source of nitrogen.
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The Germans found their source of nitrogen from
the air, which is 80% nitrogen. The Chemist
FRITZ HABER developed the Haber Process. The
Haber Process takes nitrogen from the air and
combines it with hydrogen to form ammonia
NH3 during a reversible reaction.
Increasing the yield of ammonia in the Haber Process
The ammonia produced in the Haber Process breaks down to
from nitrogen and hydrogen which then recombine to form
ammonia. This is because the Haber Process is a reversible
reaction.
For the manufacturer it is important to try to get the reaction
to go forwards more than backwards. The more the reaction
moves forwards the higher the yield of ammonia.
It has been found that the reaction is more likely to move
forwards under the following conditions:
 A high pressure
 A low temperature
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Too high a pressure however would make the reaction vessel
expensive to build and the process more dangerous. A
compromise pressure of 200 atmospheres is therefore used.
Too low a temperature would cause the reaction to become too
slow. A compromise temperature of 450˚C is therefore used.
Using Ammonia to make Fertilisers.
Once ammonia has been produced it can be made into
fertilisers to provide plants with nitrogen for growth. Firstly
the ammonia is added to water to produce the alkali ammonium
hydroxide.
NH3(g) + H2O(l)
NH4OH(aq)
(ammonium hydroxide alkali)
Secondly the ammonium hydroxide is added to an acid where it
is then neutralised and an ammonium salt plus water is
produced. The ammonium salt is the fertiliser.
Example 1 - where ammonium hydroxide is neutralised with
nitric acid to make the fertiliser ammonium nitrate.
NH4OH(aq) +
Ammonium hydroxide
HNO3
NH4 NO3
nitric acid
+ H2O
ammonium nitrate fertiliser
Example 2 - where ammonium hydroxide is neutralised with
sulphuric acid to make the fertiliser ammonium sulphate.
2NH4OH(aq) +
Ammonium hydroxide
H2SO4
(NH4)2 SO4
sulphuric acid
ammonium sulphate fertiliser
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+ H2O
Advantages of Fertilisers
1. Because they provide essential nutrients the same crops
can be grown in the same soil year after year.
2. The Farmer can choose the fertiliser to fit the crop.
For example, if the plant needs lots of potassium a
Farmer could pick a fertiliser high in potassium.
3. Fertilisers improve the overall health of plants and
generally make them less susceptible to disease.
4. Fertilisers produce larger crops so that less land is
required to grow them.
5. More food can be grown in densely populated areas
Disadvantages of fertilisers
1.
Artificial fertilisers are very soluble and end up in our
water supplies. Nitrates in the water supplies can cause
nitrogen diseases in infants such as Blue Baby Syndrome.
2. High nitrate levels in water supplies have been linked to
cancer.
3. Nitrate salts in ponds and lakes cause eutrophication
(this is where algae grow on the surface and therefore
starve the wildlife below of oxygen)
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Some more tests!
Testing for ammonium ions:
All the positively charged ions we have looked at so far
have been metal ions. Ammonium ions are also positive
ions (NH4+).
To test for ammonium ions such as those in our
fertiliser ammonium sulphate, the solution being
tested is heated with sodium hydroxide solution.
If ammonium ions are present, ammonia gas is given
off. For example:
NH4Cl(aq) + NaOH(aq)
NaCl(aq) + H2O(l) + NH3(g)
The result of this test is that a potent smell of
ammonia is given off
Testing for ammonia gas
You test the ammonia with damp red litmus paper,
which turns blue in the gas.
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END OF SUMMARY SHEETS
Nitrogen Questions
1. Who discovered Nitrogen?
_________________________________________
2. Where can nitrogen compounds be found?
_________________________________________
_________________________________________
3. Describe Nitrogen gas
_________________________________________
_________________________________________
4. Describe what happens to a banana when it is dipped
into liquid nitrogen and further hit with a hammer.
_________________________________________
_________________________________________
5. Where does nitrogen come from?
______________
6. Why do plants need nitrogen?
_________________________________________
_________________________________________
7. Why can’t plants get nitrogen directly from the air?
_________________________________________
_________________________________________
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8. Give three ways in which nitrogen can be converted
into a useable form by plants (nitrogen fixation):
a.________________________________________
_________________________________________
b.________________________________________
_________________________________________
c.________________________________________
_________________________________________
9. Give a definition of nitrogen fixation?
_________________________________________
_________________________________________
10. Write a sentence about each of the following (use
the summary sheets to help you):Fertiliser
_______________________________________
_______________________________________
The Haber Process
_______________________________________
_______________________________________
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Ammonia
_______________________________________
_______________________________________
Ammonium hydroxide
_______________________________________
_______________________________________
Sulphuric/Nitric acid
_______________________________________
_______________________________________
Ammonium sulphate/nitrate
_______________________________________
_______________________________________
11. Fill in the gaps;
The Haber Process - The Haber Process produces
________________
from
___________
and
______________.
This is a _____________ reaction carried out at a
temperature of __________ and under _____
atmospheres of pressure.
REACTION CONDITIONS
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12. From the graph below you will see that the reaction
conditions actually used in the production of ammonia do not
give the greatest yield of ammonia.
a. Looking at the graph what temperature and pressure would
give the best % (yield) of ammonia? Give units.
Temp = _________
pressure ___________
Yield of ammonia under these conditions __________
b. Using multimedia science school, look at the reaction
vessel containing nitrogen, hydrogen and ammonia. Increase
both the temperature and pressure and complete the
following:
i. Increasing the pressure of gases in the Haber Process
(increases/decreases) ______________ the yield of ammonia
produced.
Yield is the amount of nitrogen and hydrogen converted to
ammonia.
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ii. Increasing the temperature of gases in the Haber Process
(increases/decreases) ______________ the yield of ammonia
produced.
iii. Which of the following combinations would result in the
highest yield of ammonia? Circle the correct answer.
Low temp, low pressure
Low temp, high pressure
High temp, high pressure
iv. Is this combination used in the actual Haber Process?
_____
v. What is the actual temperature used? ________
vi. What is the actual pressure used? ________
vii. What catalyst is used? ________
viii. Using the above graph or multimedia science school what
is the actual yield of ammonia achieved by using these reaction
conditions? ___________
Results obtained from the graph and multimedia science school may be different.
This is because the graph in not particularly accurate. This exercise is simply to
check that you can read a graph.
Why why why?
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13. So if the reaction conditions used do
not give the greatest yield of ammonia why
don’t they use a higher pressure and lower
temperature in the Haber process?! Write
your answers below.
a. Why is a pressure of 200 atmospheres used in the Haber
process when a higher pressure would yield more ammonia?
_______________________________________________
_______________________________________________
b.
Why is a temperature of 450˚C used when a lower
temperature would produce a higher yield of ammonia?
_______________________________________________
_______________________________________________
14. Use the rest of this page to summarise the HABER
PROCESS. Include the fact that it’s a reversible reaction.
Ensure that you know the conditions – 400-500 C, 200-300
atmospheres, iron catalyst.
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Using ammonia produced in the HABER PROCESS to make
FERTILISERS.
Neutralisation - a reaction of an
acid with a base forming a salt and
water.
The base acts to remove the
hydrogen ions present in the acid
thus removing its acidity.
Fertilisers are the salts produced when ammonia solution
(NH4OH) acts as a base to neutralise acids such as sulphuric
acid (hydrogen sulphate).
Complete the following equation: ( swap partners to make the
fertiliser AMMONIUM SULPHATE),
Ammonium +
hydrogen
__________ + __________
Hydroxide
sulphate
__________
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__________
Making ammonium sulphate fertiliser from ammonia
solution and sulphuric acid
Ammonium sulphate (NH4)2SO4 is manufactured by neutralising
sulphuric acid H2SO4 with ammonia (NH3) solution (NH4OH).
Put the following sentences into the correct order by
rewriting them into the table below and draw the apparatus
required to carry out each step.

Add ammonium hydroxide 5 cm3 at a time until the
indicator turns green. This shows that the acid has been
_______________- in the table draw a diagram of a conical flask containing
25cm3 sulphuric acid + U.I. with ammonium hydroxide being added using a measuring
cylinder.

Measure out 25cm3 sulphuric acid. Pour into a conical
flask – in the table draw a diagram of a conical flask containing 25cm sulphuric acid.
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 Add 2-3 drops universal indicator to the sulphuric acid.
The colour should become ___________________ - – in
the table draw a diagram of a conical flask containing 25cm3 sulphuric acid with universal
indicator being added from a pipette.
 Now pour the salt solution into an evaporating basin.
Leave to crystallise. You should now have a sample of
ammonium sulphate fertiliser – in the table draw an evaporating
containing ammonium sulphate solution.

Repeat the whole process with the now known volume of
ammonium hydroxide (we don’t want indicator
contaminating our final salt sample) - in the table draw a diagram of a
conical flask containing 25cm3 sulphuric acid without U.I. with ammonium hydroxide being
added using a measuring cylinder.
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Plan –
draw relevant equipment with a pencil and a ruler next to each step in the correct order.
Steps for obtaining the fertiliser Equipment required.
ammonium sulphate by neutralising
sulphuric acid with ammonium
hydroxide solution.
1.
2.
3.
4.
5.
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Use page 6 to write a balanced chemical equation for the
reaction of sulphuric acid with ammonia solution to produce
ammonium sulphate and water.
____________ + ______________
___________ + ________
Now carry out an experiment to isolate the fertiliser (salt)
ammonium sulphate using ammonia solution (ammonium
hydroxide) and sulphuric acid using the above plan.
Results – fill in the text box below.
Description of ammonium sulphate salt -
You have just made ammonium sulphate fertiliser. Using page 6
of the summary sheets, write down a word and chemical
equation to explain how you can make ammonium nitrate
fertiliser.
WORD EQUATION
CHEMICAL EQUATION
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The advantages and disadvantages of
fertilisers.
Use the resource sheet below and page 6 of the summary sheets to
evaluate the advantages and disadvantages of fertiliser. Your teacher will
advise you on how to approach this.
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Fertilisers
Fertilisers can be natural, such as manure and
sewage sludge, or artificial, such as ammonium
nitrate. Nutrients from fertilisers can get washed into
rivers and leach into underground water sources.
Eutrophication is the main environmental hazard
associated with fertilisers.
RESOURCE SHEET
Why do we use fertilisers?
Farmers use fertilisers to give the crops they grow extra nutrients
than they would normally get just from the soil. This can help
farmers to increase their crop yields.
What is Eutrophication?
Eutrophication is a condition in an aquatic ecosystem where high
nutrient concentrations stimulate blooms of algae (e.g.,
phytoplankton).
High nitrate levels in drinking
waters are considered to be a
hazard to both human and animal
health.
They are associated with some
forms of cancers, such as those of
the stomach and intestines.
They may also cause "blue baby"
syndrome in babies and young
infants due to interference with
the infants’ ability to carry
oxygen in the blood
Algae remove oxygen from the water, which makes it difficult for
other plants and animals to get enough oxygen to survive.
Blue baby syndrome is a rare but sometimes fatal disease that occurs primarily during the first four months of life.
Symptoms include a blue discoloration of the lips, nose, and ears. Other symptoms include crying, vomiting and
diarrhoea.
It can be caused by a chemical called nitrate sometimes found at unsafe levels in tap water that is used to mix
powdered formula.
Extract from a Broadcast by Channel 4 in the UK, 1997 – ‘The tyranny of environmentalists’
Reaping the rewards of technology
The densely populated First World is growing more trees because of modern high-yield farming techniques.
'In the United States, 'we use less land to produce more food than we used 50 years ago. We're able to use less land
precisely because of chemical fertilisers and some of the very sophisticated techniques that we have. That allows you to
preserve more land for wildlife habitat, for open space, for forests and other purposes.
'If you look at Africa, where they use very primitive agricultural techniques, which means they have to use very large
amounts of land - that reduces the amount of land for endangered species like elephants and lions and tigers. It's also
usually very bad agriculture - there's more soil erosion. So the environmental benefits of chemical fertilisers are really
quite high.'
'It flies in the face of green theology,' adds Dennis Avery, Director of the Centre for Global Food Issues, 'but man-made
chemicals today are helping to give us the most productive, most sustainable farming in the history of the planet. The best
yields, the best soils, the more earthworms, the most soil bacteria, the most food for people, the most land left for wildlife all of it being achieved because of chemical fertilisers, pesticides, weedkillers.'
Of course the climate in Africa is not as friendly to agriculture as it is in the Western world. However, scientists argue that
with high-yield farming and irrigation Africa could feed itself many times over. The problem is not overpopulation, they
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say, it is backward farming techniques.
Teacher Demo
Describe the test and the result of the test to identify the
presence of an ammonium salt?
______________________________________________
______________________________________________
______________________________________________
Describe the test and the result of the test to identify the
alkaline gas ammonia?
______________________________________________
______________________________________________
______________________________________________
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