# How many moles of MgS_2O_3 are in 241 g of the compound?

Jun 7, 2017

$\text{1.77 moles}$

#### Explanation:

The idea here is that you can use a compound's molar mass, which tells you the mass of exactly $1$ mole of the compound, as a conversion factor to go from grams to moles or vice versa.

In this case, magnesium thiosulfate has a molar mass equal to

${M}_{{\text{M MgS"_2"O"_3) = color(blue)("136.433 g")color(white)(.)color(darkorange)("mol}}^{- 1}}$

This tells you that every $\textcolor{\mathrm{da} r k \mathmr{and} a n \ge}{\text{1 mole}}$ of magnesium thiosulfate has a mass of $\textcolor{b l u e}{\text{136.433 g}}$.

You can thus say that your sample will contain

$241 \textcolor{red}{\cancel{\textcolor{b l a c k}{{\text{g"))) * (color(orange)("1 mole")color(white)(.)"MgS"_2"O"_3)/(color(blue)(136.433)color(red)(cancel(color(blue)("g")))) = color(darkgreen)(ul(color(black)("1.77 moles MgS"_2"O}}_{3}}}}$

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