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How to Figure Millimoles of a Substance

Chemists use the mole as a unit to keep track of the quantities of chemicals used in reactions. This is useful because even a small amount of a substance can contain billions of molecules, and a mole stands for the enormous quantity of atoms or molecules -- 6.02 x 10^23. The gram molecular weight of a substance is the mass, in grams, of one mole of that compound, so you can use this mass to find out how many moles are contained in a given weight of a chemical.

Things You'll Need

Calculator

Instructions

- 1
  Enter the mass of chemical which you have, in units of grams, into the calculator. For example, if you are performing an experiment with 0.25 g of sodium chloride, or NaCl, enter 0.25.
- 2
  Divide the number you just entered by the gram molecular weight of your chemical. This calculation gives you the number of moles of that chemical. The gram molecular weight for NaCl is 58.44 g/mole, so you would calculate 0.25/58.44 to obtain 0.00428 moles.
- 3
  Multiply the result of your previous calculation by 1,000. Because there are 1,000 millimoles in a mole, this will convert your value into millimoles of chemical. In the example, you would calculate 0.00428 x 1000 and get an answer of 4.28 millimoles of NaCl.

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