IGCSE Chemistry 0620/21/O/N/21 Q31


31 Which raw material is used in the Contact process?

A air
B ammonia
C carbon
D nitrogen

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Answer ( 1 )


    Contact process is an industrial process of making sulphuric acid. The process involves the use of oxygen gas and oxygen gas can be obtained from air. Therefore, air is a raw material

    Ans: A

    Contact process:

    1. Sulphur is burnt in air to produce sulphur dioxide: S + O2 –> SO2

    2. Mixture of SO2 and excess oxygen is passed through a converter. The SO2 is oxidised to SO3 under 400-500 degree Celsius, 1 atm of pressure and with Vanadium (V) Oxide as catalyst.

    3. The sulphur trioxide is dissolved in concentrated sulphuric acid to form oleum: SO3 + H2SO4 –> H2S2O7.

    * This concentrated sulphuric acid isn’t made using Contact process, but from a method using SO3 + H2O –> H2SO4. This method isn’t recommended for making H2SO4 because the reaction is extremely vigorous and produces large amount of heat. The process also produces sulphuric acid mist that pollutes and is difficult to condense.

    4. Oleum is then diluted with water to produce concentrated sulphuric acid of about 98% : H2S2O7 + H2O –> 2H2SO4

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