That’s right, limestone – you’ve probably heard of it, and you need to know all about it for the C1 exam. Ready to learn all about limestone, its uses, reactions, and the super-special awesome limestone cycle? Well, here we go…

Limestone and its uses

Now, you’ll have heard of limestone – it’s a common enough building material, as well as many other uses – in fact, we quarry large amounts of limestone, simply because of how many uses it has. We can use blocks of limestone in building, but that’s not the only use of it for construction – it is used to make calcium oxide, and cement.

We can also make concrete by mixing cement with sand, aggregate (small rocks and pebbles) and water.

Of course, because this is chemistry, you have to know what compound limestone is – specifically, it is mainly calcium carbonate, which is CaCO3.
When we heat calcium carbonate strongly, it thermally decomposes to form calcium oxide and carbon dioxide, a process which can be done on a large scale, in lime kilns. The equation for this reaction is:

CaCO3                  –>           CaO         +           CO2

Calcium Carbonate              Calcium oxide       Carbon dioxide

You need to know the definition of thermal decomposition as well – it means “breaking down by heating”. You’ll need both parts to get the marks on a question that asks this.

Reactions of Carbonates

Of course, calcium carbonate isn’t the only carbonate out there in the universe – in fact, you have to know about different reactions of carbonates in general, not just calcium carbonate. In fact, all metal carbonates react in similar ways when heated, or when reacted with acid – producing a metal oxide and carbon dioxide when heated strongly enough (thermal decomposition) and reacting with acids to produce a salt, water, and carbon dioxide gas.

Because of this, limestone is damaged by acid rain as the acid in the rain reacts with the carbonates in the limestone.

Calcium hydroxide solution is known as limewater – something you probably know as a test for carbon dioxide. When carbon dioxide is bubbled through limewater, it reacts and produces an insoluble precipitate of calcium carbonate – causing the limewater to go cloudy.

The limestone cycle

So, you know what limestone does and some of its reactions. But there’s still more to learn – namely, about the cycle that limestone repeats. This cycle goes as follows:

  • Calcium carbonate thermally decomposes into calcium oxide and carbon dioxide when heated strongly
  • When water is added to calcium oxide it becomes calcium hydroxide
  • When excess water is added to calcium hydroxide, it dissolves slightly to make limewater
  • Carbon dioxide added to calcium hydroxide forms calcium carbonate, the main component of limestone.

You also need to know the major use of calcium hydroxide – as it is an alkali, it can be used to neutralise acids. For example, it is often used by farmers to neutralise acidic soil, and in industry it is used to neutralise acidic gases.

Cement and Concrete

Of course, pure limestone isn’t all – you’ve got to know about the substances it can be used to make, and how they are made (and what they can do). First up is… cement! In order to make cement, limestone has to be mixed with clay, and heated strongly in a kiln. The result of this is ground up to make a fine powder – cement.

This powder can be mixed with sand and water to make mortar, which is used to hold bricks and blocks together (channelling my inner Dr. Seuss here) in buildings.

In order to make concrete, we add aggregate to cement, sand and water – the aggregate used is typically small stones or crushed rock, and the resulting mixture can be poured into moulds, before it sets to form a hard solid.

Limestone issues

Like every topic in science, you also have to consider issues with limestone. Typically, we need limestone for almost all buildings – to make cement and concrete, and in some places to even make the buildings. However, quarrying limestone can have negative impacts on the environment, and on people living near the quarries.

Also, cement works are often close to limestone quarries, and uses a lot of land and energy.

Here are some advantages about areas where quarrying occurs:

  • There can be more employment opportunities for local people if there is a nearby limestone quarry
  • There are more customers and trade for local businesses
  • Roads are often improved

And here are some disadvantages about areas where quarrying occurs:

  • Dust and noise are annoying and in some cases potentially dangerous
  • Greater amount of traffic
  • Loss of habitats for wildlife

 

And that’s about it for limestone! If you have any questions, post a comment. Hope this helped!

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