Plan: Write the formula, then multiply the number of atoms (or ions) of each element by its atomic mass, and find the sum.
Solution: (a) The formula is P4S3 . Molecular mass = (4 x at. mass of P) + (3 x at. mass of S) = (4 x 30.97 amu) + (3 x 32.07 amu) = 220.1 amu
Problem: Using the data in the periodic table, calculate the molecular mass of the following compounds:
(a) Tetraphosphorus trisulfide (b) Ammonium nitrate
(b) The formula is NH4NO3 .
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Skill 7. Calculating the molecular mass of a compound
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