Year 10 ChemistryLimestone

By Mr. C Dobson

Objectives for the remainder of the year:

1. Understand what limestone is?2. How is it formed?3. How to we get it from the ground?4. Learn about the uses of limestone in

everyday life5. Discuss the negative affects on the

environment by quarrying for limestone6. Understand and carry out the various

chemical reactions associated with limestone

What is limestone?• Marble, limestone and chalk are all

made from the compound called calcium carbonate (CaCO3).

How is it formed?

• It is a sedimentary rock formed from the tiny shells of dead sea creatures

• These were compressed (squashed) over millions of years

How is limestone obtained?

• Blasting in quarries using dynamite is the most common method of obtaining limestone

USES (continued)

• Limestone is a useful building material as it is soft and can be carved easily. Due to its softness, however, it is easily eroded by the weather. It is also attacked by the acid in rainwater and in recent years acid rain, caused by atmospheric pollution, has seriously damaged a lot of limestone buildings.

• A lot of limestone is turned into lime and used in the manufacture of cement.

• Because lime is alkaline it is used in agriculture to remove acid from acid soils.It is also used in the steel industry as one of the ingredients added to a blast furnace

Erosion by weathering

Its uses

The reactions of limestoneYou will need:

• Bunsen burner• 2 boiling tubes• Safety goggles• Indicator solution• Bench matt• Tongs• 1 Filter paper

• Water• Test tube rack• Dropping pipette• pH card • Straw• Funnel• Small glass beaker

Thermal Decomposition

• When calcium carbonate is heated strongly it decomposes, forming calcium oxide (lime) and releasing carbon dioxide gas.

• Calcium carbonate (CaCO3) ---> calcium oxide (CaO) + carbon dioxide (CO2)

Making slaked lime

• When water is added to calcium oxide heat is generated, causing steam to be released, and slaked lime (calcium hydroxide) is made. Do this until it stops fizzing and you have a beaker half full.

• Calcium oxide (CaO)+ water (H2O)---> calcium hydroxide Ca(OH)2

• Slaked lime is an alkaline solution, it will turn indicator solution purple (this is added to acidic lakes to neutralise them)

Caution – goggles on, the limestone gets very hot and bits could jump out when you add the water

Getting back limestone• If you breathe into the

slaked lime you just made Ca(OH)2, you will be adding Carbon Dioxide as you breathe out (Do not suck on the straw!)

• Calcium Hydroxide Ca(OH)2 + Carbon Dioxide (CO2) ---> Calcium Carbonate (CaCO3)

Fact - The test for carbon dioxide gas is to bubble it through limewater which will turn murky. The murkiness is the formation of particles of limestone.

CaCO3Buildin

g,neutralises acid in soil + lakes

making glass,

HEAT

CO2 gas given off

CaO

Calcium carbonate

Calcium oxide

To make slaked lime

Calcium hydroxide

Neutralising acid in

soil

Ca(OH)2

Calcium hydroxide solution

Ca(OH)2

Testing for carbon dioxide

Add a little water

Add a lot of water

Bubble in CO2

gas

In the limelightA term used in theatres for the light given off by heating a piece of ‘lime’ – limestone to give off a bright light and using as a lighting source on stags or tables (see images below)

The lime kiln