Synthesising the manufacture of ammonia and its salts

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Malaysia SPM Form 4 Chemistry, Chapter 9: Manufactured Substances in Industries

Ammonia

Contents 1 Uses of ammonia 1.1 Manufacture of Fertilizers 1.2 Solvent Uses 2 Characteristic of ammonia 3 Testing for Ammonia Gas 4 The Haber Process 4.1 The reaction 4.2 Sources of the raw material 4.3 Condition 4.4 Products 5 The Manufacture of Nitric Acid (Ostwald Process) 5.1 Introduction 5.2 Reaction

[edit] Uses of ammonia

Table 3 Uses of ammonia

Use of ammonia	Percentage
fertilizers	75
nitric acid	10
solvents	8
nylon and other organic compounds	7

[edit] Manufacture of Fertilizers

• The main use of ammonia is in the manufacture of fertilizers.
• Approximately 75% of all ammonia produced is converted into various ammonium compounds like ammonium sulphate (NH4)2SO4, ammonium nitrate NH4NO3, ammonium phosphate (NH4)3PO4 and urea NH2CONH2.
• These compounds are called nitrogenous fertilizers.

Example Ammonium sulphate (NH4)2SO4 H2SO4(aq) + 2NH3(aq)  (NH4)2SO4(aq) Ammonium nitrate NH4NO3 HNO3(aq) + NH3(aq)  NH4NO3(aq) ammonium phosphate (NH4)3PO4 H3PO4(aq) + 3NH3(aq)  (NH4)3PO4(aq) Urea NH2CONH2 CO2(g) + NH3(g)  CO(NH2)2(p) + H2O(l)

• They are solids for ease in handling and water soluble so that they seep into the soil to be absorbed by the roots of the plant.
• Nitrogen is an essential element for healthy plant growth as we saw earlier with the nitrogen cycle. Nitrogen is essential for making proteins which are needed for healthy growth of stems and leaves. The proportion of nitrogen present in a particular fertiliser can be calculated and is usually quoted as an 'N' value on the fertiliser bag.

[edit] Solvent Uses

• queous ammonia is used as a degreasing agent, as it is a good solvent of grease and fat.
• Many household cleaners boast of the 'power of ammonia' for removing grease stains around the kitchen.
• However, it is wrong, as stated in some commercials, to talk of 'liquid ammonia'.
• It is more accurate to say 'ammonia solution', as ammonia does not liquefy until a temperature of -34 °C is reached.

[edit] Characteristic of ammonia

React with acid to form salt and water As an alkali, ammonia can react with acid to form salt and water. Example H2SO4(aq) + 2NH3(aq) ¾® (NH4)2SO4(aq) HNO3(aq) + NH3(aq) ¾® NH4NO3(aq) H3PO4(aq) + 3NH3(aq) ¾® (NH4)3PO4(aq)

Ammonia solution react with positive ions Ammonia dissolve into water to form ammonium and hydroxide ion. NH3 + H2O ¾® NH4+ + OH-

The hydroxide ion can react with many kinds of positive ion to form precipitate. Example Mg2+ + 2OH- ¾® Mg(OH)2 Fe2+ + 2OH- ¾® Fe(OH)2 Al3+ + 3OH- ¾® Al(OH)3

[edit] Testing for Ammonia Gas

• Ammonia is the only common alkaline gas, so it can be identified with moist red litmus paper turning blue.
• However, a more specific chemical test is to hold close to the suspected ammonia, a glass rod dipped into some concentrated hydrochloric acid.
• This will give off fumes of hydrogen chloride gas which, in the presence of ammonia, form a dense, white 'smoke' of ammonium chloride:

ammonia gas + hydrogen chloride gas - ammonium chloride NH3 (g) + HC1 (g)  NH4C1 (s)

• In the same way, mixing a gas jar of hydrogen chloride and ammonia gas produces the same dense, white smoke. The smoke again is the fine-particled solid called ammonium chloride.

[edit] The Haber Process

[edit] The reaction

• Ammonia is made by the Haber process from nitrogen and hydrogen:

N2(g) + 3H2(g)  2NH3(g); H = -92 kJ mo1-1

• The reaction is exothermic, and involves a decrease in the number of moles of gas.

[edit] Sources of the raw material

Hydrogen Hydrogen is produced industrially from cracking oil

Nitrogen Nitrogen from liquefaction of the air

[edit] Condition

Catalyst	Iron
Promoter	Aluminium oxide
Ratio of Hydrogen and Oxygen	The two gases are combined directly in a ratio of 3 : 1
Temperature	At 450 °C An application of Le Chatelier's shows that the forward reaction should be assisted by a low temperature. At low temperature, the rate of attainment of equilibrium is low. At high temperature, the position of equilibrium is over to the left. A compromise temperature is adopted, and a catalyst is employed to speed up the attainment of equilibrium concentrations.
Pressure	At 200-1000 atm An application of Le Chatelier's shows that the forward reaction should be assisted by a high pressure.

[edit] Products

• The yield is about 10%, and unreacted gases are recycled

When the ammonia has been produced, it is liquefied 'out', by reducing the temperature to -34°C (239 K)

[edit] The Manufacture of Nitric Acid (Ostwald Process)

[edit] Introduction

Industrially, nitric acid is made by the catalytic oxidation of ammonia over heated platinum. Oxidising ammonia produces oxides of nitrogen which can then be dissolved in water to produce nitric acid.

[edit] Reaction

• Initially, nitrogen(II) oxide will be formed from the catalytic oxidation of ammonia using the transition metal platinum.

ammonia + oxygen ¾® nitrogen(II) oxide + steam 4NH3 (g) + 5O2 (g) ¾® 4NO (g) + 6H2O (g)

• The nitrogen(II) oxide is rapidly cooled before combining with oxygen (from excess air) to form nitrogen(IV) oxide.

2NO (g) + O2 (g) ¾® 2NO2 (g)

• The nitrogen(IV) oxide, mixed with excess air, is then allowed to react with water to form nitric acid.

nitrogen(IV) oxide + oxygen (air) + water ¾® nitric acid 4NO2 (g) + O2 (g) + 2H2O (1) ¾® HNO3 (aq)

Uses of Nitric Acid

• Most of the nitric acid made is used to make the all-important fertilisers, such as ammonium nitrate.
• Other uses of nitric acid include making explosive, like nitroglycerine, or TNT (trinitrotoluene), and making dyes. Modern dyes are azo dyes, which can be formed by the reduction of various nitro-compounds.