Percent Composition, Empirical & Molecular Formulas

Front

What is percent composition?

Back

Percent composition is the percentage by mass of each element in a compound.

Front

How do you calculate the percent by mass of an element in a compound?

Back

Percent by mass = (mass of element in 1 mole of compound / molar mass of compound) x 100%.

Front

What is the percent by mass of fluorine in CaF₂? (Ca = 40.08 g/mol, F = 19.00 g/mol)

Back

49%.

Front

What is the percent by mass of sodium in NaCl? (Na = 22.99 g/mol, Cl = 35.45 g/mol)

Back

39%.

Front

What is an empirical formula?

Back

An empirical formula is the simplest whole-number ratio of moles of elements in a compound.

Front

What is a molecular formula?

Back

A molecular formula shows the actual number of atoms of each element in a molecule.

Front

How do you determine the molecular formula from the empirical formula?

Back

Multiply the subscripts in the empirical formula by a whole number to match the molecular molar mass.

Front

What is the molecular formula if the empirical formula is CH₂O and the molecular molar mass is 180.18? (C = 12.01 g/mol, H = 1.01 g/mol, O = 16.00 g/mol)

Back

C₆H₁₂O₆.

Front

Which pair has the same empirical formula: NaCrO₄ and Na₂Cr₂O₇, or C₂H₄O₂ and C₆H₁₂O₆?

Back

C₂H₄O₂ and C₆H₁₂O₆.

Front

What is the molar mass of CaF₂? (Ca = 40.08 g/mol, F = 19.00 g/mol)

Back

78.08 g/mol.