We do this by dividing the given mass by the molar mass of $\mathrm{BaCl}_{2}$. The molar mass of $\mathrm{BaCl}_{2}$ is 208.23 g/mol. So, we have:
\[
\frac{15.0 \, \text{g}}{208.23 \, \text{g/mol}} = 0.0720 \, \text{moles of} \, \mathrm{BaCl}_{2}
\]
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