Determine the atomic mass (amu) of each element in the compound (periodic table).
Multiply the amu by the element's subscript in the formula to determine the mass of the element in that compound.
Determine the molar mass of the compound (sum the masses of each element).
Divide each element's mass by the compound's molar mass, then multiply by 100.
Rounding - generally, round the percent composition to the nearest hundredth.
Determine Empirical Formula:
1. Convert the percent composition to mass composition (assume you have 100.0 g of the sample and convert percentages to grams; 100% = 100 g).
2. Convert the mass compositions to mole compositions (divide each mass composition by the atomic mass of the element).
3. Convert the mole compositions into a molar ratio by dividing each mole composition by the smallest mole composition of the group and then round each to the nearest whole number.
4. Use the mole ratio values as the subscripts for the empirical formula.
Question 1
1.
Determine the empirical formula for the following compound:
63.50% Ag; 8.25% N; 28.25% O
a.) Mole Compositions (4 SigFigs per blank) - from step 2:
Ag = _______ mol
N = _______ mol
O = _______ mol
b.) Molar Ratios (round to nearest whole number) - from step 3:
Ag = _______ mol
N = _______ mol
O = _______ mol
c.) Empirical Formula = _______
Question 2
2.
Determine the empirical formula for the following:
52.11% C; 13.14% H; 34.75% O
a.) Mole Compositions (4 SigFigs per blank) - from step 2:
C = _______ mol
H = _______ mol
O = _______ mol
b.) Molar Ratios (round to nearest whole number) - from step 3:
C = _______ mol
H = _______ mol
O =_______ mol
c.) Empirical Formula = _______
Question 3
3.
Determine the empirical formula for the following:
27.16% Na; 16.44% N; 56.40% O
a.) Mole Compositions (4 SigFigs per blank) - from step 2:
Na = _______ mol
N = _______ mol
O = _______ mol
b.) Molar Ratios (round to nearest whole number) - from step 3:
Na = _______ mol
N = _______ mol
O = _______ mol
c.) Empirical Formula = _______
Question 4
4.
Determine the empirical formula for the following:
37.51% C; 4.20% H; 58.29% O
a.) Mole Compositions (4 SigFigs per blank) - from step 2:
C = _______ mol
H = _______ mol
O = _______ mol
b.) Molar Ratios (round to nearest whole number) - from step 3:
C = _______ mol
H = _______ mol
O = _______ mol
c.) Empirical Formula = _______
Question 5
5.
Determine the empirical formula for the following:
38.72% C; 6.503% H; 51.59% O; 9.041% N; 14.82% Na
a.) Mole Compositions (4 SigFigs per blank) - from step 2:
C = _______ mol
H = _______ mol
O = _______ mol
N = _______ mol
Na = _______ mol
b.) Molar Ratios (round to nearest whole number) - from step 3:
