Question #93a29

1 Answer
Jan 20, 2017

#"0.114 moles K"_2"S"#


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.