Chapter 10, Problem 96A

RDA of Selenium The recommended daily allowance (RDA) of selenium in your diet is $\text{8}\text{.87 }\times {\text{ 10}}^{-4}$ mol. How many atoms of selenium is this?

Interpretation Introduction

Interpretation:

The number of atoms of selenium in given number of moles needs to be determined.

Concept introduction:

In 1 mol of any substance, there are $6.022\times {10}^{23}$ units of that substance. These units can be atoms and molecules. The number of units in 1 mol of any substance is known as Avogadro’s number. It is denoted by symbol N_A.

Explanation of Solution

There are $6.022\times {10}^{23}$ units in 1 mol of a substance. The representative particles depend on the type of the substance. For example, for a compound, the representative particles are molecules and it is atoms in the case of elements.

Thus, number of particles in given moles of substance can be calculated as follows:

$N=n{N}_A$

Here, N_A is Avogadro’s number and the value is equal to $6.022\times {10}^{23}$.

The given number of moles of selenium element is $8.87\times {10}^{-4}\text{ mol}$.

Putting the values,

$\begin{array}{l}N=\left(8.87\times {10}^{-4}\text{ mol}\right)\left(6.022\times {10}^{23}\text{ atoms/mol}\right)\\ =5.342\times {10}^{20}\text{ atoms}\end{array}$

Conclusion

Thus, the number of particles can be calculated from number of moles using Avogadro’s number. The calculated value is $5.342\times {10}^{20}\text{ atoms}$.