Download Avogadro's Number and more Lecture notes Chemistry in PDF only on Docsity! A VICTORIA SCIENCE TEACHING RESOURCE Avogadro’s Number 6.022 x 1023 or 602,200,000,000,000,000,000,000 ?WHAT IS IT? ? WHAT DOES IT MEAN? ?WHAT’S A MOLE? Avogadro’s Number is the number of atoms, molecules, or other objects that makes up one mole of a substance. For example: 6.022 x 1023 hydrogen atoms represent one mole of hydrogen. 6.022 x 1023 water molecules represent one mole of water. 6.022 x 1023 elephants represent one mole of elephants. Using Moles and Avogadro’s Number Take this reaction as an example: NaOH + HCl = NaCl + H2O. Because this looks like an even reaction on either side, it would be easy to assume that you can add equal weights of NaOH and HCl together and have them all used up in the reaction. But the elements that make those molecules up have different densities, or as scientists say their ‘atomic mass’ is different. For example, you can’t add one cup of sodium hydroxide and one of hydrochloric acid to get a complete reaction. This is because if you measure out the same volume of these chemicals you’ll have more molecules of the dense one and there won’t be an exact number to react and your end result will not be what you expect. That’s where Avogadro’s number comes in. It is a really useful way to standardise the way we predict and carry out chemical reactions, in the same way that working in teaspoons, grams or millilitres allows us to mix a perfect sponge cake. Once chemists have worked out how much a mole of a chemical weighs they can always ensure that they have approximately the right number of molecules to make a reaction work fully. ? WHY IS THAT A PROBLEM? The mole is the unit of measurement for the amount of a substance as set out by the International System of Units. Other SUI units of measurement include kilograms, metres, and seconds. It’s a very handy way for chemists to work with huge numbers of atoms or molecules. AVOGADRO’S NUMBER Avogadro didn’t discover the number himself— it was named after him in recognition of his contributions to chemistry. Avogadro’s number helps chemists to get around the problem that every element has a slightly different mass, or density.
