Question #93a29

1 Answer
Stefan V.
Jan 20, 2017

"0.114 moles K"_2"S"

Explanation:

In order to go from grams of potassium sulfide, "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 "110.26 g mol"^(-1), which means that

"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 color(red)(cancel(color(black)("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.

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