Chapter 2 - Rocks and building materials

Question 0

How can we use limestone in building material?

Answer 0

Powdered limestone can be heated with powder Clay to make cement. When we mix cement with water, sand and crushed rock, a slow chemical reaction takes place and a building material formed called concrete.

Question 1

What is limestone?

Answer 1

Limestone is a rock that is mainly made of calcium carbonate. Some types of limestone were formed from the remains of tiny plants and animals that lived on the sea millions of years ago.

Question 2

Explain the chemical formula for calcium carbonate.

Answer 2

The chemical formula for calcium carbonate is caco3, calcium ion has 2+ charge and carbonate ion has 2- charge, the opposite charge cancels out each other so chemical formula for calcium carbonate is caco3

Question 3

What happen when we heat limestone?

Answer 3

When limestone is heated strongly, it produces calcium oxide and carbon dioxide.
CaCO₃ → CaO + CO₂

Question 4

What is thermal decomposition?

Answer 4

Breaking down of chemical by heating is called thermal decomposition

Question 5

In which way we can make massive amount of Calcium oxide?

Answer 5

A rotary lime kiln can be used to produce massive amounts of calcium oxide. The kiln is filled with crushed limestone and it is heated using hot air. Calcium oxide comes out at the bottom of the kiln and the waste gases leave at the top of the kiln. The drum of kiln rotates which is why it is called a rotary kiln.

Question 6

Write down testing for Carbon dioxide.

Answer 6

We can use a simple test to find out if the gas given off is carbon dioxide. If carbon dioxide is passed through limewater, the limewater turns cloudy.
• Limewater is a solution of calcium hydroxide. It is alkaline.
• carbon dioxide is a weakly acidic gas so it reacts with the alkaline limewater.
• in this reaction tiny solid particles of insoluble calcium carbonates are formed as a precipitate.
Ca(OH)2 + CO₂ → CaCO₃ + H₂O

Question 7

Write down a reaction of carbonates.

Answer 7

Carbonates react with acids to give a salt, water and carbon dioxide. For calcium carbonate the reaction with hydrochloric acid is:
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

Question 8

How can we make calcium hydroxide?

Answer 8

When we add water to calcium oxide, it reacts to produce calcium hydroxide. This reaction gives out a lot of heat.
CaO + H₂O → Ca(OH)₂