Products from calcium carbonate
For your exam, you need to know how calcium hydroxide is obtained from calcium carbonate.
Making calcium oxide
If calcium carbonate is heated strongly, it breaks down to form calcium oxide and carbon dioxide. Calcium oxide is yellow when hot, but white when cold.
Here are the equations for this reaction: calcium carbonate calcium oxide + carbon dioxide
CaCO3 CaO + CO2
This is a thermal decomposition reaction.
Making calcium hydroxide
Calcium oxide reacts with water to form calcium hydroxide, which is an alkali. Here are the equations for this reaction: calcium oxide + water → calcium hydroxide
CaO + H2O → Ca(OH)2
A lot of heat is produced in the reaction, which may even cause the water to boil.

Limestone is a type of rock, mainly composed of calcium carbonate. Limestone is quarried (dug out of the ground) and used as a building material. It is also used in the manufacture of cement, mortar and concrete.
Reactions with acids
Carbonates react with acids to produce carbon dioxide, a salt and water. For example: calcium carbonate + hydrochloric acid → carbon dioxide + calcium chloride + water
CaCO3 + 2HCl → CO2 + CaCl2 + H2O
Since limestone is mostly calcium carbonate, it is damaged by acid rain. Sodium carbonate, magnesium carbonate, zinc carbonate and copper carbonate also react with acids: they fizz when in contact with acids, and the carbon dioxide released can be detected using limewater.
Calcium hydroxide
When limestone is heated strongly, the calcium carbonate it contains decomposes to form calcium oxide. This reacts with water to form calcium hydroxide, which is analkali. Calcium hydroxide is used to neutralise excess acidity, for example, in lakes and soils affected by acid rain.
Cement, mortar and concrete
Cement is made by heating powdered limestone with clay. Cement is an ingredient in mortar and concrete: mortar, used to join bricks together, is made by mixing cement with sand and water concrete is made by mixing cement with sand, water and aggregate (crushed rock)
Advantages and disadvantages of various building materials