What is Limestone? • Limestone is made up of the shells of millennia old dead sea creatures. • Layers of these built up over millions of years, and were squashed together until they formed limestone. • This means it is a sedimentary rock.
Types of Limestone • There three different types of limestone: • Chalk is a very soft form of limestone which has had less pressure put on it whilst it was being formed. • Marble is the hardest form of limestone, as it was subjected to lots of pressure when it was formed This is a metamorphic rock. • Limestone is the third type and is formed at a medium pressure.
Chemical Stuff • Chalk, Limestone and Marble are different forms of the same compound – calcium carbonate. • Calcium carbonate is made from carbon, oxygen and calcium and has the formula CaCO3. • Calcium carbonate is an insoluble chemical, and is also a base. (Bases neutralise acids).
The chemistry of limestone The limestone cycle (next slide) shows how 3 very important chemicals can be made from limestone: • Lime • Slaked lime and • Limewater
Key Added to substance Taken away from substance Limestone Cycle Calcium Hydroxide (AQ) Ca(OH) 2 Limestone CO2 Calcium oxide (CaO) CO2 H2O Heat Lime Water Lime H2O H2O Slaked Lime Used to detect for the presence of CO2. Turns cloudy if CO2 is bubbled through it Calcium hydroxide Ca(OH)2
Uses of limestone Limestone also has many other uses: • to make glass • in the production of paper and iron • as a building material • to make cement and to neutralise acidic soils and lakes.
Glass • Glass is made by heating a mixture of sand, limestone and soda (sodium carbonate) until it melts. • When the mixture cools it comes out as glass. • Glass is used for many everyday things such as windows, glasses and mirrors.
Paper!? • Paper is made of wood pulp. • To make this, acid is used to break the wood down. • Limewater is used to neutralise the acid, and also helps to whiten the paper. • It is also used as a bulking agent, so less trees are cut down to make the paper.
Iron • When iron is made in the blast furnace, the impurities in the iron must removed. • Limestone mixes with the impurities in the iron in the blast furnace, and forms a substance known as slag. • The slag is separated from the iron, and taken away, leaving pure molten iron which can be made into steel.
Building Stuff • Limestone has been used for building for many centuries. • Many old buildings are made out of limestone. • However, it can be gradually dissolved by acid rain.
Neutralisation • Ordinary limestone, ground into a powder, can be used to neutralise acidity in lakes and soils caused by acid rain. • The calcium carbonate is a base (an insoluble alkali), and so can neutralise the the acid. • Slaked lime works in the same way but is much faster.
Cement • When limestone is heated with clay it forms cement, a substance that sets gradually when it reacts with water. • Cement can be made into mortar by adding sand and water. Mortar is used to set the bricks in walls, as when it dries it acts as an adhesive between the bricks.
Cement (cont) • Cement can also be made into concrete by adding water, sand and small stones or gravel. • Concrete is used for all kinds of building work, including paths, walls and large buildings.
Summary • Limestone (CaCO3)is formed from seashells by a process that takes millions of years. • Limestone is used to make many things in our everyday lives, such as glass, cement, paper and buildings.