GCSE Chemistry revision

Moles

Use of amount of substance in relation to masses of pure substances

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A mole is the unit used to measure the amount of a substance, just as metres measure distance and seconds measure time.
One mole of any substance contains 6.02 imes 10²³ particles, where particles can be atoms, molecules, ions, or electrons.
The number 6.02 imes 10²³ is known as Avogadro's constant.

One mole of a substance has a mass in grams equal to its relative atomic mass (Ar) or relative formula mass (Mr).
For example, one mole of carbon (Ar = 12) has a mass of 12 g, and one mole of CO₂ (Mr = 44) has a mass of 44 g.
In every case, regardless of the substance, one mole always contains 6.02 imes 10²³ atoms or molecules.

2. Moles and Relative Atomic/Formula Mass AQA

One mole of a substance has a mass in grams equal to its relative atomic mass (Ar) or relative formula mass (Mr).
For example, one mole of carbon (Ar = 12) has a mass of 12 g, and one mole of CO₂ (Mr = 44) has a mass of 44 g.
In every case, regardless of the substance, one mole always contains 6.02 imes 10²³ atoms or molecules.

The key formula linking moles, mass, and Mr is: moles = mass (g) / Mr To find the number of moles in 42.5 g of ammonia (NH₃, Mr = 17): 42.5 / 17 = 2.5 moles The formula can be rearranged to find mass: mass = moles × Mr