How do you find the molar mass of #"Fe"_2"O"_3#?

1 Answer
Jul 15, 2016

Answer:

Here's how you can do that.

Explanation:

As you know, the molar mass of a compound tells you the mass of exactly one mole of said element. You can calculate the molar mass of a compound by using

  • its chemical formula
  • the molar masses of its constituent elements

In this case, a formula unit of iron(III) oxide, #"Fe"_2"O"_3#, consists of

  • two atoms of iron, #2 xx "Fe"#
  • three atoms of oxygen, #3 xx "O"#

This means that one mole of iron(III) oxide will contain

  • two moles of iron, #2 xx "Fe"#
  • three moles of oxygen, #3 xx "O"#

Now, the molar masses of iron and of oxygen are listed as

#M_("M Fe") = "55.845 g mol"^(-1)#

#M_("M O") = "15.9994 g mol"^(-1)#

This tells you that one mole of iron has a mass of #"55.845 g"# and one mole of oxygen has a mass of #"15.9994 g"#. Use these values to find the mass of one mole of iron(III) oxide

#overbrace(2 xx "55.845 g")^(color(blue)("the contribution of 2 moles of Fe")) + overbrace(3 xx "15.9994 g")^(color(purple)("the contribution of 3 moles of O")) = "159.6882 g"#

So, if one mole of iron(III) oxide has a mass of #"159.6882 g"#, it follows that its molar mass will be

#M_("M Fe"_2"O"_3) = color(green)(|bar(ul(color(white)(a/a)color(black)("159.6882 g mol"^(-1))color(white)(a/a)|)))#