Determining Chemical Formulas

7.4

Empirical Formula

• Empirical Formula – the ________ for the elements combined in a compound, with _________ showing the smallest whole-number mole ratio of the ____________ atoms in the compound.

Calculation

• Calculate the empirical formula of a substance that is 78.1% B and 21.9 % H.• Assume you have _____ grams total.• Use molar mass to convert to moles of

each.• Divide by the smallest # of moles.• Round to the nearest whole number.

Calculations• In a new alkaline battery, one substance

is composed of 63.0% manganese and 37.0% oxygen by mass. Determine the empirical formula of the compound in the battery.• To make sure your answer is correct,

calculate the % composition of all elements from your answer and compare.

Calculation

• Determine the empirical formula of a compound that is composed of 60.0% carbon, 13.4% hydrogen, and 26.6% oxygen.

Calculations

• Find the empirical formula of a compound found to contain 26.56% potassium, 35.41% chromium, and the remainder oxygen.

Molecular Formulas

• Molecular formula – the actual formula• x(empirical. form) = molecular form• x is a _________ number• Need the _________ ________ and the

_________________ mass to determine molecular formula

Calculation

• Diborane has a mass of 27.67 and an empirical formula of BH3. Determine the molecular formula of diborane.• The empirical formula of a compound is

found to be P2O5. The molar mass of the compound is 284 g/mol. Determine the molecular formula of the compound.

Calculations

• Determine the molecular formula of a compounds that has an empirical formula of CH and a molar mass of 78.12 g/mol.• Determine the molecular formula of

a substance that has an empirical formula of CH2O and a molar mass of 120.12 g/mol.

Calculations

• Determine the empirical formula of a substance that is 28.253% Iron and 71.747% Chlorine.• Determine the empirical formula

of a substance that is 76.880% Re and 23.120% O.