5.4 nitrogen

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- NITROGEN AND FERTILISERS- By the end of the topic students should be able to: □ State the use of nitrogen in the manufacture of ammonia. □ Describe the manufacture of ammonia by the Haber Process, including the essential conditions. □ Describe the reaction of ammonium salts with alkalis to produce ammonia gas. □ Name the need of plants for nitrogen. □ State the main use of ammonia. □ State the names and formulae of two important nitrogen fertilizers made from ammonia (i.e. ammonium nitrate and ammonium sulphate). □ Calculate the % nitrogen in fertilizers. □ Describe eutrophication and water pollution problems caused by nitrates leaching from farmland. Prepared By Kartini Ishak 1

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Page 1: 5.4 Nitrogen

- NITROGEN AND FERTILISERS-

By the end of the topic students should be able to:□ State the use of nitrogen in the manufacture of ammonia.□ Describe the manufacture of ammonia by the Haber Process, including the essential conditions.□ Describe the reaction of ammonium salts with alkalis to produce ammonia gas.□ Name the need of plants for nitrogen.□ State the main use of ammonia.□ State the names and formulae of two important nitrogen fertilizers made from ammonia (i.e. ammonium nitrate and ammonium sulphate).□ Calculate the % nitrogen in fertilizers.□ Describe eutrophication and water pollution problems caused by nitrates leaching from farmland.

Please tick in the box if you can do the above.

Nitrogen Gas

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What is the percentage of Nitogen in the atmosphere? _________

Nitrogen gas is fairly unreactive. Explain why.____________________________________________________________________________________________________________________________________

A major use of nitrogen gas is in the manufacture of ammonia.

MANUFACTURING AMMONIA BY THE HABER PROCESS

Ammonia is manufactured by the Haber Process.

The raw materials for the manufacture of ammonia in the Haber Process are ______________ and ________________.

How do you think the raw materials are obtained?____________________________________________________________________________________________________________________________________

Write the equation for the Haber Process.__________________________________________________________________

The ammonia formed is then liquefied and removed from the system. The unreacted nitrogen and hydrogen is recycled to form more ammonia.

CONDITIONS OF THE HABER PROCESS

To achieve the maximum yield of ammonia at the minimum cost, the reaction conditions are very carefully controlled.

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Figure 1 showing the graph yield of ammonia at different temperatures and pressures.

1) Effect of temperature on the yield of ammonia

Figure 1 shows the yield of ammonia at different temperatures and pressures. What can you deduce from the graph? (hint: Relationship between yield and temperature)____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2) Effect of pressure on the yield of ammonia

The yield of ammonia is increased by using high pressures. What will happen to the rate of reaction when pressure is increased?_______________________________________________________________

What problem will arise from increasing the pressure to get a better yield of ammonia?_____________________________________________________________________________________________________________________________________________________________________________________________

3) Effect of catalyst on the yield of ammonia

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A high pressure and a relatively high temperature are needed to make nitrogen react with hydrogen to form ammonia. Even then the reaction is slow, so a catalyst is used to speed up the reaction.

The common catalyst used in the Haber Process is _____________.

The reaction conditions (optimum conditions to produce a reasonable amount of ammonia in a reasonable period of time) in the Haber process includes:

Temperature:Presure:Catalyst:

Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 293, Questions, Quest. 2-5CHEMISTRY INSIGHTS, Pg. 296-297, Structured Questions, Quest. 1, 2 and 4.

PROPERTIES OF AMMONIA

Ammonia is a colourless gas with a strong smell. Ammonia is an alkali:

1) Aqueous ammonia contains _____ ions.2) It turns damp _____ litmus paper _________.3) It turns Universal Indicator blue (showing a pH of 13).4) It reacts with aqueous metal ions to give precipitates of metal hydroxides.

e.g. Fe3+(aq) + 3OH-(aq) Fe(OH)3(s) Ammonia is produced when ammonium salts react wit strong

alkalis such as sodium hydroxide.

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e.g NH4Cl + NaOH NH3 + NaCl + H2O Ammonia is produced when nitrate ions are reduced by aqueous

sodium hydroxide and aluminium metal.

Please proceed to do exercise from: CHEMISTRY INSIGHTS, Pg. 296, Structured Questions, Quest. 3.

USES OF AMMONIA

Most ammonia is used to manufacture nitrogen fertilizers. Examples of important nitrogen fertilizers:

Nitrogen fertilisers Reactions for making the fertilsersName Formula

Ammonium nitrateAmmonium sulphate

NITROGENOUS FERTILISERS

For healthy growth, plants need a wide variety of nutrients.

Three nutrients of particular importance and required in fairly large amounts are:a) Nitrogen usually in the form of nitrate ions.b) phosphorus usually in the form of phosphate ions.c) Potassium ions.

Therefore, the nutrients are the principal components of chemical fertilizers.

Most of the nitrogen fertilizers are derived from ammonia.

The more common nitrogen fertilizers are:a) Liquid ammonia, which is sometimes applied under pressure directly to the soil or bubbled into the irrigation water.

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b) Ammonium sulphate, which is produced by the reaction of ammonia with sulphuric acid.c) Ammonium nitrate, which is produced by reacting ammonia with concentrated nitric acid.d) Urea, which is made by reacting ammonia together with carbon dioxide.

The efficiency of the fertilizers depends on the amount of nitrogen added per unit mass. To compare the nitrogen content of the fertilizers, the percentage mass of nitrogen in the compound is calculated.

Example:Find the percentage mass of nitrogen in the compound, NH3. (relative atomic mass: N=14 and H=1).

Step 1: Relative molecular mass of NH3 = 17Step 2: Percentage mass of nitrogen in ammonia

= ___Mass of nitrogen in ammonia____ x 100 Relative molecular mass of ammonia

QuestionsCalculate the percentage mass of nitrogen in the following compounds:a) Ammonium sulphate, (NH4)2SO4

b) Ammonium nitrate, NH4NO3

c) Urea, (NH2)2CO

POLLUTION PROBLEMS CAUSED BY FERTILISERS

Nitrogen fertilizers can be washed out of the soil into nearby rivers, streams and lakes. This can cause two important pollution problems:

a) Eutrophication of waterIt is a condition in an aquatic ecosystem where abundant nutrient concentrations stimulate a high rate of formation of organic matter. This process is summarized in the flow chart below.

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As ammonia can be displaced from its salts by alkalis or bases, addition of alkalis or bases to soil causes more loss of nitrogen from the added nitrogen fertilizers. However, addition of a base or alkali to the soil will help to reduce the acidity of the soil.

Name one common base added to the soil in order to reduce its acidity.

_______________________________________________________________

Write down the chemical equation of the reaction between the base and ammonium nitrate.

_______________________________________________________________

b) Pollution of tap water

The fertilizer can add nitrate ions to the water, which get into tap water. Nitrate ions are poisonous.

They are believed to damage haemoglobin in the blood and can cause cancer.

Ammonium salts are also harmful, as the ammonium ions get oxidized to nitrate by bacteria in the water.

It is difficult to completely remove nitrate from tap water in treatment plants.

Please proceed to do exercise from: WORKSHEET 1WORKSHEET 2

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WORKSHEET 1

WORKSHEET 2

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