Chapter 10.1, Problem 2PP

Interpretation Introduction

Interpretation:

The number of molecules in $\text{11}\text{.5 mol of water}$ 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.

Answer to Problem 2PP

The number of H₂O molecules is $6.92\times {10}^{24}$.

Explanation of Solution

Given information:

The number of moles of H₂O molecule is 11.5 mol.

The number of moles can be converted into number of units using the following conversion factor:

$\begin{array}{l}1{\text{ mole = N}}_{\text{A}}\\ \text{1 mole = 6}\text{.022}\times {\text{ 10}}^{23}\text{ units}\end{array}$

Thus, in 11.5 mol of H₂O, the number of H₂O molecules can be calculated as follows:

$N=n\times N_A$

Putting the values,

$\begin{array}{l}N=\left(11.5\text{ mol}\right)\left(6.022\times {10}^{23}\text{ molecules/mol}\right)\\ =6.92\times {10}^{24}\text{ molecules}\end{array}$

Conclusion

Thus, in 11.5 mol of H₂O there are $6.92\times {10}^{24}$ molecules.