Calculating Molar Mass

Core Concepts

In this tutorial, you will learn how to calculate the molar mass for elements and molecules. If you enjoy this article, be sure to check out our other tutorials linked below.

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  • Molar mass: The sum of atomic weight in a molecule. It is sometimes referred to as molecular weight.
  • Compounds: Contains atoms of different elements that are combined at a fixed ratio.
    • Ex. NaCl
  • Molecules: Neutral group of atoms chemically bonded together.
    • Ex. O3, NaCl
  • Molecular formula: A way of presenting a molecule that shows the proportions of atoms.
    • Ex. NH3

How to Calculate Molar Mass

Molar mass can be calculated by using the periodic table and following three simple steps. It should be noted that this number is an average and therefore may vary due to isotopic elements.

File:Periodic-table.jpg - Wikimedia Commons

Step 1:

The first step for calculating molar mass is to identify all the elements in a given molecule and write their atomic masses using the periodic table. The atomic mass is equal to the atomic number which is listed below the element symbol. For example, if we are trying to find the molar mass of ammonia (NH3), then we need to find the atomic masses for nitrogen and hydrogen. Using the periodic table, we should get:

  • Nitrogen: 14.01g
  • Hydrogen: 1.01g

Step 2:

The second step is to determine how much of each element is present in the compound. According to the molecular formula (NH3), there is one nitrogen and three hydrogens present. So, now we will multiply these numbers by their corresponding atomic masses. It should look like this:

  • Nitrogen: 14.01g X 1= 14.01g
  • Hydrogen: 1.01g X 3= 3.02g

Step 3:

The last and final step is to add up the two products we got from multiplying. For ammonia, we should get a molar mass of 17.04 grams. Moreover, this means that 1 mol of NH3 is equal to 17.04 grams of NH3.

  • Nitrogen: 14.01g X 1= 14.01g
  • Hydrogen: 1.01g X 3= 3.03g
  • Nitrogen and hydrogen: 14.01 + 3.03 = 17.04g

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