Explain how to calculate the number of atoms of a certain element in a given mass of a compound?

To calculate the number of atoms in a formula, the weight of a sample, its atomic mass from the periodic table and a constant known as Avogadro’s number are needed.

Example: How many atoms are present in 32.80 grams of copper?

Find the molar mass of copper on the periodic table: 63.55 grams/mole.

Change that into moles using the molar mass 32.80 g of Cu × 1 mol Cu / 63.55 g Cu = 0.52 mol of Cu

Convert Moles to Atoms Using Avogadro’s Number 0.52 mol of Cu × 6.022 x 1023 atoms / 1 mol of Cu = 3.13 x 1023 molecules

32.80 g of Cu × 1 mol Cu / 159.17 g Cu × 6.022 x 1023 atoms / 1 mol of Cu = 3.13 x 1023 atoms in 32.80 grams of copper

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