4.9-4.11 Compound Molar Mass, Mass Percent Composition, Empirical Formula from Mass Data

formula mass

mass of a single molecule (or formula unit) in amu

(added up masses of all atoms that make up the molecule/formula unit)

molar mass

mass of 1 mole of molecules (6.022E23 molecules) or formula units in grams/mol

(added up molar masses of all atoms that make up the molecule/formula unit)

mass percent composition

measures the percentage contribution of each element to the total mass of a chemical compound (must contain 2 or more components/elements)

mass percent composition formula

(mass of the element in 1 mole of compound/mass of 1 mole of compound) x 100%

mass percent composition as a conversion factor

Treating the percentages as ratios out of a 100-unit sample
Because a percent means "parts per hundred," you can scale the units to whatever measurement your problem uses (such as grams or kilograms)

from the mass percent composition, what type of formula of a compound can be directly determined?

EMPIRICAL FORMULA

mass spectrometry

a technique that lets us determine the molar mass/formula mass of a compound

molar mass + empirical formula = ?

MOLECULAR FORMULA OF A COMPOUND

determining empirical formula from mass data

mass percentage of compound → masses of each component → moles of each component!!! → express ratio in lowest whole-number

determining empirical formula from mass data steps (2)

1. divide given g by molar mass on periodic table to get mol amount

2. divide both mol amounts by smallest mol amount calculated

3. write empirical formula