Calculating Formula Mass

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Background

The formula of a chemical compound is really a very compact code for the total percent composition of the compound. The first step in decoding this compact code is the determination of the formula mass or molecular mass.

To calculate the formula mass, add the masses of all of the atoms represented in the formula. Thus Al₂(SO₄)₃ translates to Al = 2, S = (1X3); O = (4X3) or Al₂S₃O₁₂ Adding all of these atom masses yields: (2XAl) + (3XS) + (12XO). Substituting the atomic masses for Al, S, and O yields: (2X27.0) + (3X32.1) + (12X16.0). Calculation of this sum yeilds: 342.1 amu (daltons).

Problem

Calculate the formula mass of the compound with the following formula:

Fe₂(SCN)₆

Atomic Masses: Fe=55.8 S=32.1 C=12.0 N=14.0 amu