Question

What is the mass, in grams, of a sample of 1.72 × 1023 atoms of potassium (K)? Show your work or explain the steps that you used to determine your answer.

Answer 1

1 mole = 6.02 x 10^23
Therefore if you go 1.72 x 10^23 / 6.02 x 10^23, you will get the amount of moles of potassium (K). Then you can use the formula moles (n) = mass (m) / molecular weight (m.w)

Rearranging for mass, you times both sides by molecular weight and get:
Number of moles x molecular weight of K = mass (m)
0.285715 moles x 39.10 g/mol = 11.17 g :)