Chemistry / Unit 3 Chem 0361 short lesson, about 20 seconds
Formula Mass for Covalent Compounds
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The idea
A covalent compound's formula mass is the sum of the average atomic masses of every atom shown in its molecular formula.
In practice
Chloroform, CHCl3, sums one carbon, one hydrogen, and three chlorine average masses to a formula mass near 119.37 amu.
Where people slip
Counting chlorine only once in CHCl3, instead of three times as its subscript requires, undercounts the formula mass by two chlorine masses.
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