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Avogadro and the Mole

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**HIGHER GRADE CHEMISTRY CALCULATIONS**

Avogadro and the Mole.. Avogadro’s constant is the number of ‘elementary particles’ in one mole of a substance. It has the value of 6.02 x 1023 mol-1. Worked example 1. Calculate the number of atoms in 4 g of bromine. Step 1:- Identify the elementary particles present Br2 molecules 1 mole x 1023 Br2 molecules Step 2:- Change from moles to a mass in grams 160g x 1023 Br2 molecules Step 3:- Use proportion. 4 g /160 x 6.02 x 1023 Br2 molecules x 1023 Br2 molecules Step 4:- Change from number of molecules to number of atoms. 1.505 x 1023 Br2 molecules 2 x x 1023 Br atoms x 1023 Br atoms

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**Calculations for you to try. **

How many atoms are there in 0.01 g of carbon? The elementary particles C atoms. 1 mole x C atoms. 12 g x C atoms. So g 0.01/12 x 6.02 x C atoms. x 1020 C atoms How many oxygen atoms are there in 2.2 g of carbon dioxide? The elementary particles CO2 molecules. 1 mole x CO2 molecules 44 g x CO2 molecules So g 2.2/44 x 6.02 x C atoms. x CO2 molecules The number of oxygen atoms 2 x 3.01 x 1022 x O atoms Higher Grade Chemistry

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**Calculations for you to try. **

Calculate the number of sodium ions in 1.00g of sodium carbonate. The elementary particles (Na+)2CO32- formula units 1 mole x 1023 (Na+)2CO32- formula units 106g x 1023 (Na+)2CO32- formula units So g 1.00/106 x 6.02 x (Na+)2CO32- formula units x (Na+)2CO32- formula units The number of Na+ ions 2 x 5.68 x 1021 x 1022 Na+ ions 4. Calculate the number of protons in 0.1g of nitrogen gas? The elementary particles N2 molecules. 1 mole x N2 molecules 28 g x N2 molecules So g 0.1/28 x 6.02 x C atoms. x N2 molecules The number of N atoms 2 x 2.15 x 1022 The number of protons 7 x 2 x 2.15 x 1022 x 1023. Higher Grade Chemistry

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**Calculations for you to try.**

5. A sample of the gas dinitrogen tetroxide, N2O4, contained x 1022oxygen atoms. What mass of dinitrogen tetroxide was present? The elementary particles N2O4 molecules 1 mole x N2O4 molecules 1 mole x x O atoms x O atoms So x O atoms mol of N2O4 2.408 x 1022 2.408 x 1024 mol 1 mole of N2O4 g So mole g Higher Grade Chemistry

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