GCSE Chemistry · AQA 8462 · Topic 4.3.2
Use of amount of substance in relation to masses of pure substances
Key points
- (Higher) Chemical amounts are measured in moles (mol). One mole of a substance has a mass in grams equal to its or .
- The Avogadro constant is particles per mole.
- Key equation: , e.g. 88 g of ( 44) is 2 mol.
- A balanced equation shows the mole ratio of reactants and products, so you can calculate the mass of product from a given mass of reactant.
- You can work out a balanced equation from masses: convert each mass to moles, divide by the smallest number of moles to get the simplest whole-number ratio.
- The limiting reactant is completely used up and limits the amount of product. Any other reactant is in excess. Doubling the limiting reactant doubles the product.
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The mole lets chemists count particles by weighing them. Most of this sub-topic is (Higher tier), except concentration in g/dm³, which everyone needs.
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