# Question bd6f7

Nov 24, 2016

$2.48 \cdot {10}^{22}$

#### Explanation:

Start by converting the sample of nitric acid from grams to moles by using the compound's molar mass

${M}_{{\text{M HNO"_3) = color(blue)("63.01 g")color(white)(.) color(brown)("mol}}^{- 1}}$

This tells you that $\textcolor{b r o w n}{\text{1 mole}}$ of nitric acid has a mass of $\textcolor{b l u e}{\text{63.01 g}}$.

In your case, the sample of nitric acid will contain

2.59 color(red)(cancel(color(black)("g"))) * "1 mole HNO"_3/(63.01color(red)(cancel(color(black)("g")))) = "0.0411 moles HNO"_3

To convert the number of moles to molecules, use Avogadro's constant

$\textcolor{p u r p \le}{\underline{\textcolor{b l a c k}{{\text{1 mole HNO"_3 = 6.022 * 10^(23)"molecules HNO}}_{3}}}}$

In your case, you will have

0.0411 color(red)(cancel(color(black)("moles HNO"_3))) * (6.022 * 10^(23)"molecules HNO"_3)/(1color(red)(cancel(color(black)("mole HNO"_3))))#

$= \textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{2.48 \cdot {10}^{22} {\text{molecules HNO}}_{3}}}}$

The answer is rounded to three sig figs.