Contact Process

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


    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.

    Sulphuric Acid

    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

    SPM Form 4 Chemistry Chapter 8 – Salts

    The Periods

    1. The period is the horizontal rows of elements in the Periodic Table.
    2. The modern periodic table has 7 periods.
    3. The period number indicates the number of electron shell.
    4. Elements in the same period have the same number of electron shells.
    5. The proton number of elements increases from left to right crossing the period.
    6. The number of electrons also increases from left to right crossing the period.

    Lanthanide and Actinide Series

    1. The sixth period has 32 elements. Due to short of space, 14 elements in the transition metal group are removed from the same horizontal row and is placed below the main table, These elements are called the Lanthanide Series.
    2. The seventh period also has 32 elements. With the same reason, 14 elements are removed from the same horizontal row and are placed below the main table, These elements are called the Actinide Series.

    Physical Change Across a Period

    There are a few major changes in physical properties across a period. For example,

    1. the state of matter changes across the period.
    2. The size of the molecule changes across the period, too.

    State of Matter

    1. The diagram above shows that the state of matter of the elements in period 2 and period 3 change from solid to gas across the period (At room temperature).
    2. In period 2, the first 4 elements are solid whereas the last 4 elements are gases. The melting point of lithium is low while the melting point of boron and carbon is very high.
    3. In period 3, the first 6 elements are solid whereas the last 2 elements are gases.
    Atomic Size
    1. As shown in the diagram above, the atomic size of elements in period 2 and period 3 decreases across a period.
    2. This is because
      1. The number of proton in the nucleus increases whereas the number of shells remains unchanged across a period.
      2. As the number of proton in the nucleus increases, the positive charge of the nucleus will also increase.
      3. The negative charge of the valence electrons will also increase due to the increase of the number of valence electrons across a period.
      4. Thus, the attraction force between the nucleus and the valence electrons is getting stronger and stronger across a period.
      5. This force will pull the valence electrons closer to the nucleus and thus reduces the atomic radius.
      6. Therefore the size of the atom decreases across a period from left to right.
    3. The diagram below shows the change in the atomic size of the elements in all seven periods. The trends can be concluded as below:
      1. The size of the atom increases down the group.
      2. The size of the atom decreases across a period from left to right.
      3. For transition metal, the size of the atom does not have obvious change across a period.

      Chemical Properties Change Across a Period

      1. There is a gradual chemical change across a period.
      2. The acidity (or basicity) of the oxide of element changes across a period.
      3. The metallic properties, the electronegativity of the element also change across a period.

      Acidic Oxide or Basic Oxide

      From left to right across a period the oxides change from alkaline/basic (with metals e.g. Na2O) to acidic (with non-metals e.g. SO2).

      Metal, Metalloid and Non-metal

      1. As we go across a period from left to right, the elements change from metals to non-metals.
      2. There are about 7 elements in the periodic table are classified as semi-metals.
      3. The metals in the periodic table are mainly found in the left-hand columns (Groups 1 and 2) and in the central blocks of the transition elements.
      4. On the right-hand side of the periodic table, there are 7 semi-metals form a staircase-like pattern, act as a divider between metal and non-metal.
      5. The semi-metals are also called the metalloid.

      Uses of Metalloids

      1. The most widely used semi-metals are silicon and germanium.
      2. It is used to make diodes and transistors in the electronic industry.


      1. Electronegativity is a measure of the potential of atoms to attract electrons to form negative ions.
      2. Metals have low electronegativities.
      3. Non-metals have high electronegativities.
      4. Electronegativities of the elements increase across a period with increasing proton number. This is because
        1. as the proton number increases, the positive charge of the nucleus will increase accordingly.
        2. this will increase the ability of the atom to attract electrons from the surrounding and thus increase the electronegativity of the atom.

      Physical Properties of Alkali Metals

      Physical Properties of Alkali Metals

      NameProton numberElectron arrangement
      1. All Group 1 metal exist as solid at room temperature and hence have all the typical metallic properties, such as:
        1. good conductors of heat
        2. good conductors of electricity,
        3. high boiling points,
        4. shiny surface (but rapidly tarnished by air oxidation).
      2. Nevertheless, Group 1 metals also show some non-typical metallic properties, such as:
        1. low melting points,
        2. low density (first three floats on water),
        3. very soft (easily squashed, extremely malleable, can be cut by a knife).

      Important trends down the group:

      1. size of atoms increases
      2. the melting point and boiling point decrease
      3. the density increases.
      4. the hardness decreases.

      Size of Atom

      1. Down the group, the size of atom increases.
      2. This is due to the increase in the number of electron shells.
      3. An atom with more shells is bigger than an atom with fewer shells.

        Boiling Point and Melting Point

        Namemelting pointboiling pointDensity g/cm3
        Francium27ºC677ºC> 1.87
        1. The melting point and boiling point generally decrease down the group.
        2. All the atoms of Group 1 metals are bonded together by a force called the metallic bond.
        3. The strength of the metallic bond depends on the distance between the atoms. The closer the atoms, the stronger the bond.
        4. Down the group, the size of the atoms increases, causing the distance of the atoms increases.
        5. As the distance between the atoms increases, the metallic bond between the atoms decreases.
        6. Therefore, less energy is needed to overcome the metallic bond during the melting process.
        7. Consequently, the melting point of Group 1 metal decreases down the group.


        1. The densities of Group 1 metals are low compared with the other metals.
        2. The densities of the first 3 elements (Lithium, Sodium and Potassium) are lower than water. Thus, they can float on the surface of the water.
        3. Nevertheless, the density increases steadily down the group.
        4. The density of a substance is given by the equation “Density=Mass/Volume”.
        5. Down the group, both the mass and the volume increase, but the increase of mass is faster than the volume, hence the density increases down the group

        MCQ – Particulat Nature of Matter


        1. Which of the following statements is not true?
          1. Matter is anything that occupies space and has mass.
          2. The particle theory of matter states that matter is made up of a large number of tiny and discrete particles.
          3. The kinetic energy of the particles in a matter increases if its temperature increases.
          4. The particles in all kind of matter are identical.
        2. Which of the following shows the correct comparison of the average kinetic energy of the particles in a solid, liquid and gas for a given substance?
          1. Solid > Liquid > Gas
          2. Solid < Liquid < Gas
          3. Solid = Liquid = Gas
          4. It depends on what kind of substance it is.
        3. The diagram shows the arrangement of particles in a substance. Which of the following is not the characteristic of the substance in this state?
          1. Particles move randomly and slowly and sometimes will collide against each other.
          2. The volume of the object is not fixed.
          3. Particles are not arranged in order. Most of the particles are still in contact with one another.
          4. Difficult to be compressed.
        4. Which of the following statements is not true about the particles in a gas?
          1. The particles of gas move at high speed
          2. The collision between the gas particles and the wall of the container is elastic.
          3. The gas particles move randomly in all direction.
          4. The gas particles are arranged in regular patterns.
        5. Which of the following take place when water solidifies to become ice?
          1. Water molecules get nearer to each other.
          2. Energy is absorbed from the surrounding.
          3. Water molecules are not arranged orderly.
          4. The mass increase.
        6. Which of the following substances sublimes at room pressure when heated?
          1. Iodine
          2. Dry ice (Solid carbon dioxide)
          3. Naphthalene
          4. Ammonium Chloride
        7. The particle theory of matter states that
          Matter is made up of a large number of tiny and discrete particles.
          Which of the following phenomenon does not support this hypothesis?
          1. Brownian Motion
          2. The shape of a solid is fixed.
          3. Diffusion of bromine vapour in gas.
          4. The volume of a substance increase when it transforms from a liquid into gas.

        Take the Test

        [WpProQuiz 3]

        Three States of Matter – Structured Question 4

        Structure Question 4:
        Figure (a)
        Figure (b)

        Figure (a) shows the set-up of the apparatus to investigate the heating process of substance Y. In this experiment, solid substance Y was heated in a water bath from room temperature until it turned into gas. Substance Y was stirred throughout the whole experiment. The temperature of substance Y was recorded at fixed intervals of time and the graph of temperature against time during the heating of substance Y is shown in Figure (b) above.


        1. What is the physical state of naphthalene at the region
          1. QR
            solid and liquid
          2. ST
            liquid and gas
          3. TU
            Gas only
        2. What is the time when substance Y begins to melt?[1 mark]

        3. What is the boiling point of substance Y?[1 mark]
        4. Why the temperature of M remains unchanged from time t3 to t2 even though heating continues?
          From t1 to t2, substance Y is melting. The heat supply to the substance is used to overcome the strong attraction force between the solid particles. No heat energy is used to increase the kinetic energy (temperature) of the particles.
        5. Why water bath is used for heating the solid of substance Y?To ensure uniform heating on substance-Y
        6. Give a reason why water bath is suitable in this experiment?Because the melting point and boiling point of substance Y is lower than the boiling point of water.
        7. Name 2 substance, whose boiling point can be determined by using water bath.
          Alcohol and ether
        8. Given that the boiling point of substance X is around 105°C. Why can’t we use water bath to determine the boiling point of substance Y?The boiling point of water is 100°C, which means the maximum temperature that can be achieved by water is 100°C, which is lower than the boiling point of substance-X.
          Substance X can not be boiled by using water bath.
        9. Suggest another method which can replace water bath in this experiment.Use oil bath or sand bath instead of water bath.
        10. Why stirring of substance Y is required throughout the whole experiment?So that heat is spread evenly throughout the substance.
        11. Compare the kinetic energy of particles of substance Y at t1 and t3.The kinetic energy of particles at t3 is higher than the kinetic energy of particles at t1.
        12. State one different in the arrangement of the particles of substance Y before t1 and after t4.Before t1, particles are arrange in an orderly manner and close to one another. After t4, the particles are very far apart and randomly arrange.

        Three States of Matter – Structured Question 3

        Structure Question 3:
        The table below shows the melting and boiling points of three different substances.

        Melting Point
        Boiling Point


        1. What is the physical state of H, I and J at room temperature (25°C)?
          H: gaseous I: solid J: liquid
        2. Which substance diffuses the fastest at room temperature? Explain your answer.
          Substance H. Because substance H exist as a gas at room temperature, hence there is a lot of empty space between the particles. Other than that, the particles of H have the highest kinetic energy.
        3. Draw some diagrams to show the arrangement of particles of substance I at 40°C, 80°C and 120°C.At 40°C

          At 80°C

          At 120°C

        4. What is the name of the process which atoms or molecules of a substance in liquid state gain sufficient energy to enter the gaseous state below boiling point?
        5. Define boiling point.
          Boiling Point is the temperature at which the pressure exerted by the surroundings upon a liquid is equalled by the pressure exerted by the vapour of the liquid.
        6. Sketch the graph of temperature against time for substance I when it is cooled from 120°C to room temperature.

        Three States of Matter – Structured Question 2

        Structure Question 2:

        An experiment is conducted to study the change of state of iodine. Some powder of solid iodine is heated as shown in the Figure above, the black solid iodine changes into a purple gas at 125°C. The purple gas is then cooled by a round bottom flask that fill with ice.


        1. State the process of change of state demonstrated by iodine at 125°C.
        2. What can be observed at part R?

          Some black powder form at the bottom of the flask.

        3. What is the name of the process when iodine gas turns into iodine solid again?

          Reverse/inverse sublimation

        4. Explain why palm oil is used in the experiment instead of water.

          Because iodine sublime at 125°C, the temperature which is higher than the boiling point of water.

        5. Name two other substances which also sublime at atmospheric pressure (1atm).

          Ammonium chloride, carbon dioxide, naphthalene.