Limestone is pretty boring right? Well read on and you’ll actually find out that you are completely…well…right…but you need to know about it for the exam. Plus it made some pretty swanky buildings so it’s not all bad.
- Limestone is mainly calcium carbonate – CaCO3
- It thermally decomposes. Thermal decomposition just means a substance chemically changes into two or more substances when it’s heated. With limestone those substances are calcium oxide and carbon dioxide.
CaCO3 CaO + CO2
Magnesium, copper, zinc and sodium carbonates do a similar thing when heated
e.g CuCO3CuO + CO2
Calcium carbonate also reacts with acid to make a calcium salt, carbon dioxide and water.
e.g. CaCO3 + H2SO4 → CaSO4 + CO2 + H2O
calcium carbonate + sulfuric acid → calcium sulfate + carbon dioxide + water
The type of salt depends on the type of acid…e.g. hydrochloric acid would make chloride and sulfuric acid make calcium sulfate.
Other carbonates that react with acids are magnesium, copper, zinc and sodium.
Calcium Oxide Reacts With Water To Produce Calcium Hydroxide
Calcium Oxide + Water → Calcium Hydroxide /OR/ CaO + H2O → Ca(OH)2
Calcium hydroxide is an alkali which is often used to neutralise acidic soil. It is also used to test for carbon dioxide. If you make a solution of calcium hydroxide in water (called limewater) and bubble a gas through it, it will turn cloudy if there is carbon dioxide in it. This cloudiness is caused by calcium carbonate being formed.
Calcium hydroxide + carbon dioxide → calcium carbonate + water
Ca(OH)2 + CO2 → CaCO3 + H2O
Other Uses Of Limestone
- Powdered limestone is heater in a kiln with powdered clay to make cement.
- Cement can be mixed with sand and water to make mortar (the grey stuff that holds bricks together).
- Cement can be mixed with sand, water and gravel to form concrete.
Advantages and Disadvantages of Using Limestone
Quarrying limestone can cause some problems:
- Ugly holes in the ground
- Often rocks are blasted apart with explosive during the quarrying process which is not great in quiet, scenic areas
- It can destroy the habitats of animals and birds
- Limestone needs to be transported from the quarry. This is usually done by lorries that causes pollution and more noise
- Waste materials are put in tips.
- Cement factories make a lot of dust which can lead to some people having breathing problems.
- Energy is needed to produce the cement – this can come from burning fossil fuels which causes pollution.
There are positives though:
- Limestones makes things people want like houses and roads – also some dyes, paints and medicines come from limestone too.
- Soil, lakes and rivers that have become acidic (often through acid rain) can be neutralised using limestone.
- Limestone is used in power station chimneys to neutralise sulfur dioxide – the cause of acid rain!
- Quarries provide jobs which brings money to the local economy which in turn can lead to improvements in transport, roads, recreation facilities and health.
- Often as part of planning permission for a quarry landscaping and restoration are usually required once quarrying is complete.
Limestone Products Advantages and Disadvantages
Limestone and concrete can be used as building materials…and in some cases with better results than others.
- Limestone is widely available, cheaper than granite or marble and is fairly easy to cut into shape.
- Some limestone is more hard-wearing than marble and it can still look attractive
- Concrete can be poured into moulds to make blocks than can be joined together. It is also a quick and easy way to constructing buildings
- However concrete is really unattractive
- Limestone, concrete and cement do not rot when wet like wood. They don’t get eaten away by insects or rodents and they are fire-resistant.
- Concrete doesn’t corrode like lots of metals do – but it does have a fairly low tensile strength so can crack/ If it’s reinforced by steel bars though it is much much stronger.