Patterns of Reactivity:
Calculating Empirical Formula from % Comp:
What is the emp form of a compound with 68.4% chromium and 31.6% oxygen?
1. Convert percentages to grams.
2. Convert grams to moles.
68.4g Cr/ 52g Cr = 1.315g Cr
31.6g O/ 16g O = 1.975g O
3. Divide by the smaller mole
1.315 Cr/ 1.315 Cr = 1 Cr
1.975g O/ 1.315 Cr = 1.5 O
4. OPTIONAL: Multiply the previous answers into a small number that will turn them into whole numbers
1 Cr x 2 = 2 Cr
1.5 O x 2 = 3 O
Cr2O3 is empirical formula
Molecular Formula from Empirical Formulas:
Cr2O3 is emp form with molar mass of 304 g/mol
1. Divide the known molar mass by the mass of one mole of emp form.
(304g/mol) / [(52x2)+(16x3)]g/mol)= 2
2. Multiply answer by the subscripts of emp form
Cr4O6 is molecular formula