LIMESTONENoadswood Science,

2011

LimestoneTuesday, April 18, 2023

To know what limestone is, and how it can be decomposed using heat

Limestone

Limestone is a rock that is made mainly of calcium carbonate, CaCO3

Some types of limestone were formed from the remains of tiny animals and plants that lived in the seas millions of years ago

When it is heated, it breaks down to form calcium oxide and carbon dioxide

Calcium oxide reacts with water to produce calcium hydroxide

Limestone and its products have many uses, including being used to make mortar, cement, concrete and glass

Thermal Decomposition

Metal carbonates such as calcium carbonate break down when heated strongly – thermal decomposition

Calcium carbonate → Calcium oxide + Carbon dioxide

CaCO3 → CaO + CO2

The products are a metal oxide (CaO) and carbon dioxide

Metals high up in the reactivity series (e.g. calcium) have carbonates that need a lot of energy to decompose them whilst metals low down in the reactivity series (e.g. copper) have carbonates that are easily decomposed

Quicklime

If limestone is heated strongly, it breaks down to form calcium oxide and carbon dioxide – via a thermal decomposition reaction

Calcium oxide is also called quicklime (yellow when hot, white when cold)

Calcium carbonate → Calcium oxide + Carbon dioxide

CaCO3 → CaO + CO2

Slaked Lime

Calcium oxide reacts with water (“slaked”) to form calcium hydroxide, also called slaked lime

Calcium oxide + Water → Calcium hydroxide

CaO + H2O → Ca(OH)2

A lot of heat is produced in the reaction

Reaction Summary

Calcium carbonate(limestone)

Calcium hydroxide(slaked lime)

Calcium oxide(quicklime)

+ carbon dioxide

Calcium hydroxide solution

(limewater)

heat

waterwater + filter

+ CO2

Experiment

Your task is to carry out the thermal decomposition reaction: -

1. Set up a test tube in a clamp stand – to this be ready to place a delivery tube in the top connected to another test tube containing limewater

2. Add 5g of calcium carbonate to the test tube and heat using the Bunsen – this will produce calcium oxide (quicklime) + carbon dioxide

3. Stop heating, and when cool add some water – this will produce calcium hydroxide (slaked lime)

4. Finally add UI – this will show how alkaline the product is (and why it is useful for neutralisation purposes)!

*During the experiment identify your mass at the start of calcium carbonate and your final mass of calcium oxide (quicklime) – how much CO2 has been produced?

Limestone Uses

The main uses of limestone and its products are: - Limestone (CaCO3) can be used as a building material

and in the manufacturing of iron Glass - heated with sand and soda (sodium carbonate) Cement - heated with clay in a kiln

Concrete - mixed with sand, water and crushed rock Mortar - mixed with sand and water

Quicklime - heated Slaked lime (Calcium Hydroxide Ca(OH)2) - mixed with

water Lime mortar - mixed with water

Limestone, quicklime and slaked lime are all used to neutralise excess acidity in lakes and in soils

Limestone Uses

Limestone is used as a building material, and to purify iron in blast furnaces. It is also used in the manufacture of glass, and of cement (one of the components of concrete)

Glass is made by melting sand and then cooling it – flat sheets of glass for windows are made by floating molten glass on a layer of molten tin

Glass manufacturers add sodium carbonate to sand during the manufacturing process, to reduce the melting temperature of the sand and so save energy – the sodium carbonate decomposes in the heat to form sodium oxide and carbon dioxide, but this makes the glass soluble in water

Calcium carbonate (limestone) is therefore also added, to stop the glass dissolving in water – the calcium carbonate decomposes in the heat to form calcium oxide and carbon dioxide

Limestone Industry

The main advantages and disadvantages of the limestone industry are as follows…

Advantages Disadvantages

Limestone is a valuable natural resource, used to make things

such as glass and concrete

Limestone quarries are visible from long distances and may

permanently disfigure the local environment

Limestone quarrying provides employment opportunities that support the local economy in

towns around the quarry

Quarrying is a heavy industry that creates noise and heavy traffic,

which damages people's quality of life

Limestone Products