A gold sample contains 90% of gold and rest is copper. How many atoms of gold are present in 1g of this sample of gold??

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Solution

We are given that the sample of gold contains 90% of gold. Therefore, mass of gold present in 1g of the sample
= [(90) X 1] / 100
= 0.9 g
The molar mass of gold is 79g. This means that there are 6.023 X 10²³ atoms of gold present in 79g of gold. So
79g of gold = 6.023 X 10²³ atoms of gold
1g of gold = (6.023 X 10²³ / 79) atoms of gold
0.9g of gold = [(6.023 X 10²³ X 0.9)/ 79] atoms of gold
= 6.861 X 10²¹ atoms of gold

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