Chemistry chapter 9

9.1 Sulphuric Acid Uses of Sulphuric Acid
Manufacture fertilisers
Manufacture paint pigments
Manufacture detergents
Manufacture synthetic fibres
Clean metals
Manufacture plastics
As an electrolyte in car batteries
Manufacture other chemicals

THE CONTACT PROCESS
Produces more than 90% of the world’s sulphuric acid
Raw materials used for the manufacture of sulphuric acid are sulphur, air and water
3 stages:
Production of sulphur dioxide
Conversion of sulphur dioxide to sulphur trioxide
Production of sulphuric acid

STAGE 1: The manufacture of sulphur dioxide
Sulphur is melted, and sprayed into the air and heated to 1000oC. The sulphur burns violently to give sulphur dioxide. The heat produced is used to help run the rest of the factory.
Write out the equation. S(g) + O2(g) -----> SO2(g) DeltaH298 = -297 kJ mol-1
Why will this enthalpy value not be the same for the reaction at the factory?
This value is for standard temperature 298oC. At the factory the temp is 1000oC.
Question:
The burning of sulphur produces a mixture of gases, about 10% sulphur dioxide and
10% oxygen by volume. What does the remaining 80% of this gas mixture consist of,
and what do these figures tell you about the combustion of sulphur.
The remaining gas mixture conatins unreacted gases from the air ( nitrogen and argon). If all the oxygen in the furnace was used up in combustion the final mixture would contain about 20% sulphur dioxide by volume. This would hamper the second stage as more oxygen would need to be added.

STAGE 2- the manufacture of sulphur trioxide
The sulphur dioxide is reacted with more oxygen in a reversible reaction to give sulphur trioxide. Write the formula below:
2SO2(g) +O2(g)<---->2SO3(g) DeltaH298 = -98 kJ mol-1
Add heat to the equation and then write Kc for this reaction
Kc = [SO3]2[heat]/[SO2]2[O2]
For the forward reaction comment on the pressure- is it increased or decreased-why?
It is decreased as there are less molecules.
Using Le Chateliers principle answer the following questions with a view to maximising the percentage of sulphur trioxide

a. Should the sulphur trioxide be removed as it is formed? Yes if it is removed then the reaction will try and counteract this and end up producing more sulphur trioxide. b. Should the temperature be high or low? Low as it is exothermic and will shift ----> if less heat. c. Should the pressure be high or low? High as there are less molecules on the right side so the equilibrium will shift ---> at high pressure. ~@@~Platinum has been used as a catalyst but it is expensive and easily poisoned by impurities so vanadium (v) oxide ( formula = V2O5) is used with traces of potassium sulphate ( formula =K2SO4).

STAGE 3- the manufacture of sulphuric acid
Sulphur trioxide reacts with water to produce sulphuric acid. Write the equation below:
H2O(l) +SO3(g) ---> H2SO4(aq) DeltaH = -130 kJ mol-1
If water is used on its own a corrosive mist of sulphuric acid is produced which can not be condensed and is a pollutant.
The sulphur trioxide is absorbed into 98% sulphuric acid forming oleum, a dense oily liquid that is a solution of sulphur trioxide in sulphuric acid. The oleum is diluted in water to obtain the required concentration of sulphuric acid (a very exothermic reaction).

Sulphur dioxide and environmental pollution
Acid Rain causes many environmental problems.
1. Acid rain corrodes buildings, monuments and statues made from marbles and sandstone. The calcium carbonate in the marble reacts with sulphuric acid from the rain to form calcium sulphate.
2. Acid rain corrodes metallic structures. The iron from the steel bridges reacts with sulphuric acid to form Iron(II) Sulphate.
3. Acid rain increases the acidity of water in lakes and rivers. Fish and other aquatic organisms which cannot live in acidic water may die. Acid rain disturbs the ecosystem.
4. Acid rain increases the acidity of soil. Most plants cannot grow well in acidic soil. The reaction of sulphuric acid with aluminium compounds in the soil forms Aluminium Sulphate which can damage the roots of trees. The damaged roots are easily attacked by viruses and bacteria. As a result, the trees die of a combination of malnutrition and diseases.

5. Acid rain leaches minerals and nutrients in the soil. The acid can react with the minerals in the soil to form soluble salts. The dissolved salts are carried by the rainwater into rivers and lakes. As a result, plants lack of sufficient essential nutrients for growth.

Thank You…. Prepared by, Clara Ting Ling Sin Ying Ting Bee Jia

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Chemistry chapter 9

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