Moles in A-Level Chemistry

I chose chemistry as an a-level because I'm quite good at it and I got an 8 in my GCSEs, however, the only thing I am worried about is moles, as they really confuse me. Are moles a big part of A-Level OCR A Chemistry or is it something I don't really need to worry about?

Reply 1

charco

Study Forum Helper

Original post by yellowdoor134

Don't worry about moles. It is just a way of doing quantitative chemistry - and you will soon get the hang of it.

It just revolves around the fact that atoms are so small that it does not make sense to measure their actual masses. Instead tha mass of an atom (and all particles made from atoms) are measured on a scale in which the ¹²C atom is used as a reference and all other atoms are compared to that being equal to exactly 12.0000.

On this scale, helium has a relative mass of 4, magnesium 24, etc.

Why is this useful?

Because it means that 12g of carbon will have the same number of particles as 4g of helium and 56g of iron and 32g of sulfur and 24g of magnesium etc.

We refer to the compared mass of the particles as the "relative mass", as they are relative to ¹²C = 12.

So what is a mole?

Simply speaking, it is the number of ¹²C atoms in 12.000 g of carbon, which is equal to Avogadro's number = 6.0223 x 10²³.

So 12 g of carbon contains the same number of particles as 32g oxygen (O₂ molecules) which = 6.0223 x 10²³.

To avoid using the rather irritating number 6.0223 x 10²³, we can just say "1 mol" of particles.

Check out this video:

You want to learn about moles and test yourself, you can register for free at www.colourful-solutions.com for a 1 month trial.

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