1. Products from limestone

2. What is thermal decomposition?
Limestone is a valuable material because it can be used as the starting point for many other materials.
When limestone is heated strongly, a chemical reaction takes place. Calcium carbonate breaks down and forms calcium oxide and carbon dioxide. This type of reaction is called thermal decomposition.
A lime kiln is often used for this reaction. The limestone is heated to 900 °C. This method has been used for centuries.
What is the word equation for this reaction?
calcium carbonate
calcium oxide
carbon dioxide  +

3. What about other metal carbonates?
Other metal carbonates can decompose in a similar way to calcium carbonate, when they are heated.
For example, when magnesium carbonate is heated it breaks down to form magnesium oxide and carbon dioxide.
magnesium carbonate
magnesium oxide
carbon dioxide  +
The general equation for the thermal decomposition of a metal carbonate is:
metal carbonate
metal oxide
carbon dioxide  +
What products are formed when copper carbonate decomposes on heating?

4. Is this a balanced reaction?
During a chemical reaction, atoms are not created or destroyed. This means that the numbers of atoms on both sides of a balanced symbol equation are always the same.
calcium carbonate
calcium oxide +
carbon dioxide 
CaCO3 
CaO +
CO2
number of atoms
before reaction
number of atoms after reaction
element
calcium
carbon
oxygen 1 1 1 1 3
1+2 = 3

5. How is slaked lime made?
Calcium oxide, a product of the thermal decomposition of limestone, is also called quicklime.
Quicklime is used as an industrial drying agent and to make slaked lime.
Uses of slaked lime include glass manufacture and neutralisation of the effects of acid rain.
Slaked lime is made by adding water to quicklime.
The chemical name for slaked lime is calcium hydroxide.
What is the word equation for this reaction?
calcium oxide
water
calcium hydroxide  +

6. Why does CO2 turn limewater cloudy?
Fully dissolving calcium hydroxide in water forms limewater.
Limewater is used to test for carbon dioxide.
When carbon dioxide gas is bubbled through limewater, the limewater becomes cloudy.
The carbon dioxide reacts with calcium hydroxide to form calcium carbonate and water.
The solid calcium carbonate is held in suspension which gives the limewater a cloudy appearance.
What is the word equation for this reaction?
calcium carbonate
calcium hydroxide (aq)
carbon dioxide  +
water

7. What is cement? Cement is used as a binder in concrete and mortar.
It is made by heating limestone or clay and adding gypsum (a compound from limestone). This mixture is then ground into a powder.
After the powder is mixed with water, it will harden to form a strong glue.
Mortar is made from cement, water and sand. It is used in bricklaying and stonework.
An even layer of mortar is spread between the bricks or stones to hold them firmly together.

8. How is concrete made?
Concrete is harder than mortar. It is sometimes described as an artificial rock.
Concrete is made from sand, cement and water but it is harder than mortar because it also contains gravel.
It is used for the foundations of buildings and for large structures such as car parks.
What is the word equation for making concrete?
cement
sand
water
concrete + 
gravel

9. What is reinforced concrete?
Although concrete is a very hard material, it is not very flexible. This means that when it is stretched it can break. Concrete has a low resistance to tension forces.
Steel rods are used to increase the strength and flexibility of concrete. This is called reinforced concrete.
This material can support 300 to
500 times the combined mass of steel and concrete it is made from.
Reinforced concrete has many uses including lamp-posts, railways and as a structural material to support buildings.

10. Summary of uses of limestone products
The products of limestone have many uses.
Quicklime, calcium oxide, is used in making steel and as an industrial drying agent. It can be mixed with water to form slaked lime.
Slaked lime, calcium hydroxide, is used to make the building materials mortar and glass. Slaked lime is alkaline. It can be sprayed on agricultural fields to reduce soil acidity and on lakes to neutralise the effects of acid rain.
Limewater is made by fully dissolving slaked lime in water. It is often used to test for carbon dioxide. This is because limewater turns cloudy in the presence of carbon dioxide.

11. Summary of limestone chemistry
Limestone and its products can be involved in various useful chemical reactions:
thermal decomposition of limestone
calcium carbonate
calcium oxide
carbon dioxide  +
production of slaked lime
calcium oxide
water
calcium hydroxide  +
using limewater to test for carbon dioxide:
calcium carbonate
calcium hydroxide (aq)
carbon dioxide  +
water