# Question #485ae

Jul 26, 2017

$1.80 \cdot {10}^{22}$ $\text{atoms}$

#### Explanation:

You should know that in order to get from grams to atoms, you need to go through moles first.

So you will need to use the molar mass of barium chloride to convert the sample to moles, Avogadro's constant to convert the number of moles of barium chloride to formula units, and the chemical formula of the salt to convert the number of formula units to a number of atoms.

Since every formula unit of barium chloride contains

• one barium cation, $1 \times {\text{Ba}}^{2 +}$
• two chloride anions, $2 \times {\text{Cl}}^{-}$

you can say that every formula unit of barium chloride contains $3$ atoms, i.e. $3$ atoms react in order to produce $1$ formula unit of barium chloride.

This means that you will have

$2.08 \textcolor{red}{\cancel{\textcolor{b l a c k}{{\text{g"))) * overbrace((1 color(red)(cancel(color(black)("mole BaCl"_2))))/(208.23color(red)(cancel(color(black)("g")))))^(color(blue)("molar mass")) * overbrace((6.022 * 10^(23)color(red)(cancel(color(black)("formula units BaCl"_2))))/(1color(red)(cancel(color(black)("mole BaCl"_2)))))^(color(blue)("Avogadro's constant")) * "3 atoms"/(1color(red)(cancel(color(black)("formula unit BaCl}}_{2}}}}$

$= \textcolor{\mathrm{da} r k g r e e n}{\underline{\textcolor{b l a c k}{1.80 \cdot {10}^{22} \textcolor{w h i t e}{.} \text{atoms}}}}$

The answer is rounded to three sig figs, the number of sig figs you have for the mass of barium chloride.