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

1 Answer
Jun 7, 2017

Answer:

#"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_ ("M MgS"_2"O"_3) = color(blue)("136.433 g")color(white)(.)color(darkorange)("mol"^(-1))#

This tells you that every #color(darkorange)("1 mole")# of magnesium thiosulfate has a mass of #color(blue)("136.433 g")#.

You can thus say that your sample will contain

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