Science & Technology in Action

1st Edition

Producing an Essential Chemical

CRH

This lesson deals with the chemistry and production process of lime. It also describes some of the many uses to which lime is put in the building, agricultural, industrial and environmental sectors. An interesting topic is the production of magnesium oxide from seawater.
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Contains the full lesson along with a supporting toolkit, including teachers’ notes.

Lesson excerpt

Lime is a vital chemical
Lime is one of the most important chemicals and has been used by people all over the world from early times. In this lesson we look at the chemistry of lime, how it is manufactured and some of its many uses.

How is lime made?
It is remarkable that the process used by the earliest cultures to produce lime is still in use today. It is easy to make providing you have limestone and a hot fire. If you get a really strong fire going on limestone(calcium carbonate) and let it burn overnight, lime will be formed under it. This lime shows as a white patch. The equation for its formation is

CaCO3 = CaO + CO2

The limestone has been converted to lime(calcium oxide) and carbon dioxide. Calcium oxide is also known asquicklime.

The place in which limestone is burned is called a limekiln. Old limekilns are found all over Ireland because lime was essential for many uses. It could be easily made, providing there was a supply of limestone in the locality. Lumps of limestone were piled on top of a fire. The temperature had to reach between 900 and 1100°C and the kiln would be left to burn for a week or more. This means that it was a batch process. The heating of limestone to produce calcium oxide is known ascalcination. Modern kilns operate acontinuous process. Limestone is fed on a conveyor into the kiln and the product (lime) is fed out and stored in bags for sale.

Quiz questions

  1. Limestone is sodium carbonate false
  2. The process for producing lime from limestone was discovered recently false
  3. Calcium oxide is called lime true
  4. Slaked lime is calcium dioxide false
  5. Slaked lime is also called quicklime false
  6. In a batch process there is a constant supply of raw material and final product false
  7. Lime cannot burn the skin false
  8. Mortar is a mix of lime and sand true
  9. Lime is good for neutralising acid in soils and in lakes true
  10. Slaked lime is used in the production of magnesium oxide from seawater true
  11. The place in which limestone is burned at high temperatures is called a hydrator false
  12. If you mix lime, sand, water and stones you get cement false

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