Question

How many moles of oxygen (O) atoms are in a sample of 3.98 × 1023 atoms? 0.661 mol O 1.51 mol O 6.60 × 1022 mol O 2.40 × 1047 mol O

Answer 1

To find moles from any number of atoms, always divide by the constant called Avogadro's Number. This number is representative of the number of atoms or molecules in a mole of any substance and is equal to about $6.022* 10^{23}$.

So, for this problem, we take the number of atoms of oxygen and divide by Avogadro's Number. 

$\frac{3.98* 10^{23} O_{2} atoms }{6.022* 10^{23} atoms/mol } = 0.6609 moles$

Answer: 0.661 moles (after rounding)

Make sense?