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Limestone

What you need to know

Reflections and Exam tips

 

Limestone and its uses

Limestone is mainly composed of the compound calcium carbonate (CaCO3). Limestone is a sedimentary rock which was formed from the shells of sea creatures that lived millions of years ago.

Limestone is quarried and can be used to produce cement, glass and concrete.

Cement

Limestone is heated with clay to make cement in a rotary kiln. The rotary kiln is heated to about 900°C and the calcium carbonate undergoes thermal decomposition to produce calcium oxide.

calcium carbonate →   calcium oxide + carbon dioxide

            CaCO3         →            CaO    +       CO2

The energy costs are high and this produces carbon dioxide (CO2). This contributes to global warming and climate change.

Mortar

Cement is mixed with sand to make mortar.

Concrete

Cement is mixed with sand and aggregate to make concrete which can resist crushing or squashing forces. The concrete can be strengthened by adding steel rods to form reinforced concrete.

The Lime Cycle

Calcium carbonate

Calcium carbonate can be decomposed by heating (thermal decomposition) to make calcium oxide and carbon dioxide.

calcium carbonate →   calcium oxide + carbon dioxide

            CaCO3         →            CaO    +       CO2

The carbonates of magnesium, copper, and zinc decompose on heating in a similar way. However, the more reactive the metal carbonate is the more heat energy is required.

Calcium oxide

Calcium oxide (slaked lime) reacts with water to produce calcium hydroxide (limewater).

calcium oxide + water → calcium hydroxide

CaO(s) + H2O(l) → Ca(OH)2(s)

Calcium hydroxide is an alkali that can be used in the neutralisation of acids.

Calcium hydroxide

A solution of calcium hydroxide (limewater) reacts with carbon dioxide to produce calcium carbonate.

calcium hydroxide solution + carbon dioxide → calcium carbonate + water

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

Limewater (calcium hydroxide) is used as a test for carbon dioxide. Carbon dioxide turns limewater cloudy/milky.

Reaction of carbonates

Carbonates react with acids to produce a salt, carbon dioxide and water. For example:

Calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide + water.

Limestone is damaged by acid rain.

Limestone issues

Limestone Quarrying

In order to get the limestone, explosives are used to blast it from quarries. Transported using large lorries to be processed.

Advantages Disadvantages

Local jobs (directly and indirectly) which improves local economy

Limestone is supplied to industry (iron extraction, added to bread, cosmetics, paper)

 Improve infrastructure (road links/by-pass)

 After use the quarry can be re-beautified and used for leisure activities (recreational lakes)

Revenue/jobs maintained after quarry closes

Many sites are located in National Parks.

 Areas of habitat are destroyed

 Some sites have unique/rare wildlife

 Blasting scares off wildlife

 Increased traffic noise

 Increased air pollution from lorries and explosions

 Increased risk of road accidents

 Dust pollution to nearby properties as well as affecting yield

 

Describe limestone and its uses

Describe thermal decomposition of limestone

Describe what happens when calcium oxide reacts with water

Draw a diagram to represent the limestone cycle

Describe what happens at a quarry

Identify problems associated with quarrying

Consider the views of different people affected by quarrying