# Question 93a29

Jan 20, 2017

$\text{0.114 moles K"_2"S}$

#### Explanation:

In order to go from grams of potassium sulfide, $\text{K"_2"S}$, to moles of potassium sulfide you must use a conversion factor.

This conversion factor is given by the molar mass of the compound. As you know, the molar mass of a compound tells you the mass of exactly $1$ mole of said compound.

In your case, potassium sulfide has a molar mass of ${\text{110.26 g mol}}^{- 1}$, which means that

$\text{every mole of K"_2"S" stackrel(color(white)(color(red)("has a mass of")aaa))(->) "110.26 g}$

You want to go from grams to moles, so set up the molar mass as

("1 mole K"_2"S")/"110.26 g"#

Now all you have to do is to multiply the number of grams of potassium sulfide by this conversion factor

$12.6 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{g"))) * ("1 mole K"_2"S")/(110.26color(red)(cancel(color(black)("g")))) = color(darkgreen)(ul(color(black)("0.114 moles K"_2"S}}}}$

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