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How to Calculate the Number of Moles Using Percent Mass

A mole is a base measurement in chemistry. A mole contains 6.02214 x 10^23 particles. A mole of an atom is equal in mass to the atomic mass, or weight, of the element in grams. Percent mass, or mass percent, is the percentage a component makes up of a total compound. Converting from mass percent to moles is helpful when trying to determine the chemical formula for the provided components.

Instructions

- 1
  Find the number of moles of each component in a compound containing the following percent masses: 38.5 carbon, 24.32 hydrogen and 37.18 oxygen. Assume a sample size of 100 grams of the compound.
- 2
  Look up the atomic masses, or weight, of each compound on the periodic table: carbon is 12.0107, hydrogen is 1.00794 and oxygen is 15.9994. Note that the atomic masses are in terms of moles per gram.
- 3
  Calculate the moles of each component by dividing its percent mass by its atomic mass: Carbon = 38.5 / 12.0107 = 3.20547512 moles carbon, Hydrogen = 34.32 / 1.00794 = 34.0496458 moles hydrogen and Oxygen = 37.18 / 15.9994 = 2.32383714 moles oxygen. Round to a certain number of significant figures if the teacher specifies; for example, rounded to four significant figures the answers would be 3.205 moles carbon, 34.05 moles hydrogen and 2.324 moles oxygen.

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