C1.2:Limestone and Building Materials

Limestone is mainly calcium carbonate - CaCO3 - and is quarried from the ground.

THERMAL DECOMPOSITION - The breaking down of a substance using heat

Limestone can be thermally decomposed to make calcium oxide and carbon dioxide.

Calcium Carbonate > Calcium Oxide + Carbon dioxide

CaCO3 > CaO + CO2

e.g. Magnesium Carbonate > Magnesium Oxide + Carbon Dioxide

       MgCO3 > MgO + CO2

Calcium carbonate reacts with acid to make a calcium salt, carbon dioxide and water meaning that limestone is damaged by acid rain.

Calcium Carbonate + Acid > Calcium Salt + Carbon Dioxide + Water

e.g. Calcium Carbonate + Sulfuric Acid > Calcium Sulfate + Carbon Dioxide + Water

       CaCO3 + H2SO4 > CaSO4 + CO2 + H2O 

e.g. Calcium Carbonate + Hydrochloric Acid > Calcium Chloride + Carbon Dioxide + Water

       CaCO3 + 2HCl > CaCl2 + CO2 + H2O 

Limestone is broken down to make calcium oxide.

When water is added to calcium oxide it forms calcium hydroxide.

Calcium Oxide + Water > Calcium Hydroxide

CaO + H2O > Ca(OH)2

Uses of calcium hydroxide:

• calcium hydroxide is an alkali so neutralises acidic soils in fields
• calcium hydroxide in solution (limewater) can be used to test for carbon dioxide. If you bubble gas through it, the solution will turn cloudy if carbon dioxide is in the gas

Calcium Hydroxide + Carbon Dioxide > Calcium Carbonate

Ca(OH)2 + CO2 > CaCO3

Limestone can be used to make other building materials such as:

• powdered limestone and powdered clay are heated in a kiln to make cement
• cement is mixed with sand to make mortar
• cement, sand and aggregate (water and gravel) make concrete

BENEFITS of limestone, concrete and cement - don't rot when wet, can't be gnawed by insects, fire-resistant

USES of limestone:

• makes chemicals used in making dyes, paints, medicines etc.
• neutralises acidic soil and acidity in lakes/rivers caused by acid rain
• neutralises sulfur dioxide (causes acid rain) in power station chimneys
• limestone quarries and associated businesses provide jobs for people and bring more money into the local economy leading to local improvements in roads, health etc.

PROBLEMS of QUARRYING limestone:

• involves making huge ugly holes damaging the landscape permanently
• quarrying processes (e.g. blasting rocks apart with explosives) create lots of noise and dust
• destroys the habitats of animals and birds
• limestone is carried away from the quarry in lorries creating more noise and pollution
• waste materials produce unsightly tips

PROBLEMS of limestone PRODUCTS:

• cement factories make lots of dust causing breathing proplems in certain people
• energy needed to produce cement involves burning fossil fuels which causes pollution
• concrete is an unattractive building material which also has low tensile strength and can crack