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Mass Percent Composition Problem

Calculation of Mass Percent Composition

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Sodium Bicarbonate or Baking Soda

Sodium Bicarbonate or Sodium Hydrogen Carbonate

Martin Walker

This is a worked example problem showing how to calculate mass percent composition.

Problem

Bicarbonate of soda (sodium hydrogen carbonate) is used in many commercial preparations. Its formula is NaHCO3. Find the mass percentages (mass %) of Na, H, C, and O in sodium hydrogen carbonate.

Solution

First, look up the atomic masses for the elements from the Periodic Table. The atomic masses are found to be:

Na is 22.99
H is 1.01
C is 12.01
O is 16.00

Next, determine how many grams of each element are present in one mole of NaHCO3:

22.99 g (1 mol) of Na
1.01 g (1 mol) of H
12.01 g (1 mol) of C
48.00 g (3 mole x 16.00 gram per mole) of O

The mass of one mole of NaHCO3 is:

22.99 g + 1.01 g + 12.01 g + 48.00 g = 84.01 g

And the mass percentages of the elements are

mass % Na = 22.99 g / 84.01 g x 100 = 27.36 %
mass % H = 1.01 g / 84.01 g x 100 = 1.20 %
mass % C = 12.01 g / 84.01 g x 100 = 14.30 %
mass % O = 48.00 g / 84.01 g x 100 = 57.14 %

Answer

mass % Na = 27.36 %
mass % H = 1.20 %
mass % C = 14.30 %
mass % O = 57.14 %

When doing mass percent calculations, it is always a good idea to check to make sure your mass percents add up to 100% (helps catch math errors):

27.36 + 14.30 + 1.20 + 57.14 = 100.00

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