Question #010b9

1 Answer
Dec 24, 2017

Answer:

Convert the moles to the mass of the element.

Explanation:

Example:

What is the molar percentage and mass percentage of each element in carbon dioxide?

Carbon dioxide has two oxygen atoms combined with one carbon atom: #CO_2#.

One "mole" of #CO_2# thus contains one "mole" of carbon, #C#, and one "mole" of oxygen, #O_2#, or TWO "moles" of #O# (it's important to know how you are defining your elements).

Let's use the ATOMIC definition for this example, so we have two "moles" of #O# in each mole of #CO_2#. The TOTAL moles of atoms in #CO_2# is then three (3).

So then, our "molar percentages" of #O# and #C# are:
#O = (2 " mole " O)/(3 " moles") = 0.667 " mole"% O#
and
#C = (1 " mole " C)/(3 " moles") = 0.333" mole"% C#

To find the mass percentage we need to multiply a mole unit by the molecular weight. This is #12 " for " C and 16 " for " O#.

Again, we have 2 moles of "O", so it will have a mass of #2 xx 16 = 32#
The carbon will have a mass of #12# because there is only one mole.

Thus, the mass of a mole of #CO_2# is #44# and the mass percentages are:
#O = 32/44 = 0.727" mass"% O#
and
#C = 12/44 = 0.273" mass"% C#