# Question #0de15

Apr 15, 2016

${A}_{r} = 58.99$

#### Explanation:

The number of moles of a substance is given by:
$\frac{m a s s \left(g r a m s\right)}{\text{Relative atomic mass} , {A}_{r}}$

And one mole comprises (Avogadro's constant), ${N}_{A} = 6.022 \times {10}^{23}$ atoms / molecules.

So number of atoms is given by:
$\frac{m a s s \left(g r a m s\right) \cdot {N}_{A}}{\text{Relative atomic mass} , {A}_{r}}$

In this case

$\left(\frac{16.26 \times {10}^{-} 3 g}{A} _ r\right) \cdot \left(6.022 \times {10}^{23}\right) = 1.66 \times {10}^{20}$

Rearranging gives:

${A}_{r} = \left(16.26 \times {10}^{-} 3 g\right) \cdot \frac{6.022 \times {10}^{23}}{1.66 \times {10}^{20}}$
so
${A}_{r} = 58.99$