Calculation of Formula or Molecular Mass

CALCULATIONS BASED ON FORMULAE

7.1 - Calculation of Formula Mass

Use the periodic table to determine the formula mass of one formula unit of ammonium sulfate. The chemical formula of ammonium sulfate (ie- the formula unit) is (NH₄)₂SO₄.

Solution:

Step 1: Figure out how many atoms of each element there are in one formula unit.

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Step 2: Use the periodic table to figure out the atomic mass of each element in the formula unit.

Step 3: Multiply the number of atoms (from step 1) of each element by its atomic mass (from Step 2) to obtain the mass of that particular element in one formula unit.

Step 4: Add up the masses of each element(from Step 3) to get the formula mass of the compound.

Step 1:	Figure out how many atoms of each element there are in one formula unit. Need some help? Click here.
Step 2:	Use the periodic table to figure out the atomic mass of each element in the formula unit.
Step 3:	Multiply the number of atoms (from step 1) of each element by its atomic mass (from Step 2) to obtain the mass of that particular element in one formula unit.
Step 4:	Add up the masses of each element(from Step 3) to get the formula mass of the compound.

Summary:

Types of Atoms Number of atoms
(Step 1) Atomic Mass
(Step 2) Mass of each type of atoms
(Step 3)

N 2 14.007 amu 28.014 amu

H 8 1.008 amu 8.064 amu

S 1 32.06 amu 32.06 amu

O 4 15.999 amu 63.996 amu

Formula Mass of (NH₄)₂SO₄(Step 4) 132.134 amu

Types of Atoms	Number of atoms (Step 1)	Atomic Mass (Step 2)	Mass of each type of atoms (Step 3)
N	2	14.007 amu	28.014 amu
H	8	1.008 amu	8.064 amu
S	1	32.06 amu	32.06 amu
O	4	15.999 amu	63.996 amu
Formula Mass of (NH₄)₂SO₄(Step 4)	132.134 amu

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