Avogadro

What is a mole?

• One mole of a substance contains \(6 \times 10^{23} \) atoms or molecules of that substance.
• \(6 \times 10^{23} \) is known as Avogadro's constant.
• One mole of a substance weighs the same as the relative atomic or molecular (formula) of that substance in grams.
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• Legenda: Amedeo Avogadro

Slide 2

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• Legenda: Cover the aspect of the triangle that you would like to find, then multiply if the remaining aspects are horizontal neighbours, or divide if they touch vertically.

Examples

• Example 1: How many moles are there in 18g of carbon?
• \(\text{Using the triangle on the previous slide, Moles =} \frac{Mass}{\text{Molecular mass}}\)
• \(\text{Therefore, }\frac{18}{12}=1.5moles\)
• Example 2: How many grams are there in 4.5 moles of calcium carbonate?
• \(Mass = Moles \times \text{Molecular mass}\)
• \(\text{So, Mass = 4.5} \times 100 = 450g\)
• Example 2: 3 moles of an element has a mass of 21g. What is the element?
• \(\text{Molecular mass =} \frac{Mass}{\text{Moles}}\)
• \(\text{Therefore, the element has an atomic mass of 7g. It is lithium.}\)