Manufacture Substances in Industry

Ostwald Process

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Ostwald Process

Introduction

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

Reaction

  1. Initially, nitrogen(II) oxide will be formed from the catalytic oxidation of ammonia using the transition metal platinum.
    Ammonia + Oxygen → Nitrogen(II) Oxide + Steam
    4NH3 (g) + 5O2 (g) → 4NO (g) + 6H2O (g)
  2. The nitrogen(II) oxide is rapidly cooled before combining with oxygen (from the excess air) to form nitrogen(IV) oxide.
    2NO (g) + O2 (g) → 2NO2 (g)
  3. 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 → Nitric acid
    4NO2 (g) + O2 (g) + 2H2O (1) → HNO3 (aq)

Uses of Nitric Acid

  1. Most of the nitric acid made is used to make the all-important fertilisers, such as ammonium nitrate.
  2. Other uses of the 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.

Characteristics of Ammonia

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Characteristics of Ammonia

  1. Ammonia gas can turn a moist red litmus paper to blue.
  2. As an alkali, ammonia can react with acid to form salt and water.
    Example
    H2SO4(aq) + 2NH3(aq) → (NH4)2SO4(aq)
    HNO3(aq) + NH3(aq) → NH4NO3(aq)
    H3PO4(aq) + 3NH3(aq) → (NH4)3PO4(aq)
  3. Ammonia dissolve into water to form ammonium and hydroxide ion.
    NH3 + H2O→ NH4+ + OH–
  4. The hydroxide ion can react with many kinds of positive ion to form precipitate.
    Example
    Mg2+ + 2OH– → Mg(OH)2
    Fe2+ + 2OH– → Fe(OH)2
    Al3+ + 3OH– → Al(OH)2

Testing for Ammonia

  1. Ammonia is the only common alkaline gas so it can be identified with moist red litmus paper turning blue.
  2. Concentrated ammonia when reacts with concentrated hydrochloric acid produces white fume.
    Ammonia gas + Hydrogen chloride gas → ammonium chloride
    NH3 (g) + HC1 (g) → NH4C1

Haber Process

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Haber Process

  1. Ammonia is manufactured in industries through Haber Process.
  2. In the Haber process, nitrogen gas, N2 from the air is mixed with hydrogen gas, H2 derived mainly from natural gas.
  3. The mixture is compressed to a high pressure of 200 atmospheres at a temperature of about 450°C.
  4. Iron is used as a catalyst to speed up the rate of reaction.
  5. Chemical equation below shows the reaction.
    N2 (g) + 3H2 (g) → 2NH3 (g)
  6. About 98% of mixture are converted into ammonia, NH3.
  7. The unreacted nitrogen gas, N2 and hydrogen gas, H2 is recycled and passed back into the reactor together with the new source of nitrogen gas, N, and hydrogen gas, H2.

Summary

Ammonia

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  1. Ammonia is a compound of nitrogen and hydrogen with the formula NH3.
  2. It is a colourless gas with a characteristic pungent smell.
  3. Ammonia is an essential compound in industry.
  4. Although in extensive use, ammonia is both corrosive and hazardous.

Uses of Ammonia

  1. The uses of ammonia include
    1. manufacturing nitrogenous fertilisers
    2. as a cooling agent in refrigerator
    3. to prevent coagulation of latex
    4. as raw material to manufacture nitric acid (Ostwald process)
    5. to make explosive
    6. as cleaning agent to remove grease

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Environmental and Health Issues of Sulphur Dioxide

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Environmental and Health Issues of Sulphur Dioxide

Sulphur dioxide, SO2 is one of the by-products of the Contact Process. It is one of the sources of environmental pollution.

Acid Rain

  1. Sulphur dioxide (SO2) is the pollutant primarily associated with acid rain.
  2. Acid rain occurs when pH of the rain is between 2.4 and 5.0. This is due to the reaction of sulphur dioxide, SO2 with rainwater.
    SO2 + H2O→ H2SO3
  3. The negative effect of acid rains includes
    1. corrosion of concrete building and metal structure.
    2. corrosion of monuments and statues made from marble
    3. causes erosion of top soil.
    4. killing aquatic life.

Health Effects

  1. SO2 is an irritant when it is inhaled and at high concentrations may cause severe problems in asthmatics such as narrowing of the airways, known as bronchoconstriction.
  2. Asthmatics are considerably more sensitive to the effects of SO2 than other individuals.

Sources of SO2

  1. The principal source of SO2 is from the combustion of fossil fuels in domestic premises and, more importantly, non-nuclear power stations.
  2. Other industrial processes such as manufacturing of sulphuric acid also contribute to the presence of SO2 in the air.

Contact Process

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Contact Process

Sulphuric Acid is Manufactured in Industry

  1. Sulphuric acid, H2SO4 is manufactured in the industry through Contact Process.
  2. The raw materials used are sulphur, air and water
  3. The Contact process consists of four stages.

    Stage 1

    1. Molten sulphur is burnt in dry air to produce sulphur dioxide
    2. The gas produced is then purified and cooled.
      S + O2 → SO2
    3. Sulphur dioxide can also be produced by burning metal sulphides such as lead(II) sulphide or zinc sulphide in dry air.
      2PbS + 3O2 → 2PbO + 2SO2

    Stage 2

    1. In a converter, sulphur dioxide and excess oxygen are passed through vanadium(V) oxide.
    2. vanadium(V) oxide act as a catalyst to expedite the process.
    3. The optimum condition for the maximum amount of product are as follow:
      1. Temperature: 450 – 500 °C
      2. Pressure: 2 – 3 atm
    4. About 99.5% of the sulphur dioxide, SO2 is converted into sulphur trioxide, SO3 through this reversible reaction.

    Stage 3

    Sulphur trioxide is dissolved in concentrated sulphuric acid to form oleum （H2S2O7）.
    SO3 + H2SO4 → H2S2O7

    Stage 4

    The oleum, H2S2O7 is then diluted with water to produce concentrated sulphuric acid, H2SO4 in large quantities.
    H2S2O7 + H2O → 2H2SO4

    Note:

    1. The two reactions in the third and fourth stages are equivalent to adding sulphur trioxide, SO3 directly to water.
      SO3 + H2O→ H2SO4
    2. However, this is not done in the industry because sulphur trioxide, SO3 reacts too violently with water.
    3. This produces a lot of heat and a large cloud of sulphuric acid, H2SO4 mist.
    4. The mist is corrosive, pollutes the air and is difficult to condense.
    Summary

    Sulphuric Acid

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    1. Sulphuric acid is a highly corrosive strong mineral acid with the molecular formula H2SO4.
    2. Sulphuric acid is a diprotic acid.
    3. Sulphuric acid has a wide range of applications. It is also a central substance in the chemical industry.

    Uses of Sulphuric Acid

    1. Applications of sulphuric acid include
      1. manufacturing fertiliser
      2. manufacturing detergent
      3. manufacturing pesticide
      4. manufacturing synthetic fibre
      5. as electrolyte in lead-acid accumulator
      6. removing metal oxide
      7. manufacturing paint
    (Click on the image to Enlarge)

    SPM Form 4 Chemistry Chapter 9 – Manufactured Substances in Industry

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    Revision Notes

    1. Sulphuric Acid
      1. Contact Process
      2. Environmental and Health Issues of Sulphur Dioxide
    2. Ammonia
      1. Haber Process
      2. Characteristics of Ammonia
      3. Ostwald Process
    3. Alloy
      1. Copper Based Alloy
      2. Iron Based Alloy
      3. Aluminium Base Alloy
      4. Tin Based Alloy
    4. Polymer
      1. Polymerisation
      2. Plastics
      3. Synthetic Rubber
      4. Synthetic Fibre
      5. Issues in Using Synthetic Polymers
    5. Glass and Ceramics
      1. Glass
      2. Ceramics
      3. New Uses of Glass and Ceramics
    6. Composite Material

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