# How do you find out a mole?

### Nathan Rawle

Oxford Master of Biochemistry - boss of Biology, Chemistry, Physics, and Maths

Find the atomic or molecular mass of a solid ⛰ or liquid ☔️ and stick a “g” for grams after it. There is one mole of that substance in that many grams of it. To find the number of moles in any mass of the substance, calculate: [mass (in grams)] / [relative atomic or molecular mass] For a gas 💨, there is one mole of that gas in 24 litres of it (or 24 dm^3) at room temperature and pressure (20°C and 1 atm). To find the number of moles in any volume of a gas (at rtp), calculate: [given volume (in dm^3)] / 24 Eg1: Lithium has an atomic weight of 6.941. Therefore, 6.941 grams of lithium contain 1 mole of lithium. Eg2: Sodium chloride has a molecular mass of 58.44. Therefore, 58.44 grams of sodium chloride contain 1 mole of sodium chloride. Eg3: Hydrogen is a gas at rtp. Therefore, at room temperature and pressure, 24 dm^3 of hydrogen gas contain 1 mole of hydrogen. Eg4: water has a molecular weight of 18.015. A litre of water weighs 1kg. 1kg = 1000g. 1000 / 18.015 = 55.509. There are 55.509 moles of water in 1 litre. Eg5: Oxygen is a gas at rtp. 6 dm^3 oxygen gas contains 6/24 = 0.25 moles of oxygen. If you’d like more chemistry tuition, please contact me through my profile 👨‍🔬! ⚛️

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