Question

Tia has a sample of pure gold (Au). She weighed the sample and the result was 12.6 grams. Tia wants to determine the number of atoms in the sample. Calculate the number of atoms in 12.6 g of pure gold.

Answer 1

Given mass of gold(Au) is , m = 12.6 g

We know that molar mass of Au is 197 (g/mol)

So number of moles , n = mass/molar mass

                                   = 12.6 g / 197 (g/mol)

                                   = 0.064 mol

Therefore the number of atoms in the sample is 0.064 mol

-----------------------------------------------------------------------------------------------------------

We know that 1 mole of any compound contains avagadro number(6.023x10²³) of atoms

                                   OR

197 g(1 mole) of Au contains 6.023x10²³ atoms

12.6 g of Au contains N atoms

N = (6.023x10²³ x12.6) / 197

   = 3.85x10²² atoms

Therefore the number of atoms in 12.6 g of pure gold is 3.85x10²² atoms