Percent Composition
Complete each question on your own sheet of paper. Show your work .

Warm Up Practice

1. How many atoms are found in one mole of mercury? 6.02 x 1023 atoms

2. 84.7 g of lead represents how many moles of lead? 0.409 mol

3. How many moles are represented in 201.7 g of copper (II) chloride? 1.500 mol

4. How many atoms of bismuth are found in 15 g of bismuth (III) bicarbonate? 2.3 x 1022 atoms

5. 0.00370 mol of lithium oxide contains how many oxygen atoms? 2.23 x 1021 atoms

6. 1.9718 x 1020 molecules of boron trioxide weighs how many grams? 0.019259 g

7. How many moles are represented by one carbon atom? 1.66 x 10-24 mol

8. How many molecules are in 10.5 g of diphosphorus pentaoxide? 4.45 x 1022 atoms

9. What is the molar mass of iron (III) phosphate? FePO4 is 150.82 g/mol

Empirical and Molecular Formulas

  1. A new barium-nitrogen compound was discovered. When the sample was analyzed, it was found to be 76.5% (by weight) barium. What is the empirical formula of the sample? BaN3
  2. There are two common oxides of sulphur. One contains 32 g of sulphur for each 32 g of oxygen. The other oxide contains 32 g of sulphur for each 48 g of oxygen. Find the empirical formula of each. SO2 and SO3
  3. A form of phosphorus, used in match heads, is called red phosphorus. When 0.062 g of red phosphorus burns, 0.142 g of phosphorus oxide is formed. What is the empirical formula of this phosphorus oxide compound? P2O5
  4. Find the simplest formula for a compound that is 79.9% copper and 20.1% sulphur. Write the name of the compound. Cu2S
  5. A compound is 24.4% Ca, 17.1% N and 58.5% O. Calculate the empirical formula. CaN2O6
  6. Find the simplest formula for a compound that is 63.6% iron and 36.4% sulphur. Write the name of the compound. FeS & iron (II) sulphide
  7. A compound is composed of 19.01 g of carbon, 18.48 g of nitrogen, 25.34 g of oxygen, and 1.58 g of hydrogen. Find the empirical formula of this compound. C6N5O6H6
  8. A chemical compound is analyzed and found to contain 6.07 g of Mg and 36.9 g of Br. The molar mass of this compound is 552.3 g/mol. Find the empirical and molecular formulas? MgBr2 & Mg3Br6
  9. A compound is composed of 16.66 g of carbon and 3.49 g of hydrogen. The molar mass of the compound is 58 g. Find the empirical formula and molecular formula for this compound. C2H5 & C4H10
  10. A compound is composed of 7.20 g of carbon, 1.20 g of hydrogen, and 9.60 g of oxygen. The molar mass of the compound is 180 g. Find the empirical and molecular formulas for this compound. CH2O & C6H12O6
  11. A 21.7 g sample of aluminum chloride sample is analyzed and found to contain 13.3% Al and 86.7 % chlorine (by mass). What is the empirical formula? AlCl5
  12. What is the molecular formula of a compound that is analyzed and found to contain the following elements in the following percentage: carbon = 27.3 % and oxygen = 72.7 % (percent by mass)? The molecular molar mass is 308 g/mol. C7O14
  13. The empirical formula for a compound is C2H5O and its molecular mass is 135 g/mol. Determine the molecular formula. C6H15O3
  14. Hydroquinone, a chemical used for photographic developing, is 65.45% C, 5.51% H and 29.09% O. Calculate the empirical and molecular formula. The molecular mass is 110 g/mol. C3H3O1 and C6H6O2
  15. A sample of "mung" is analyzed and found to contain the following element amounts: carbon = 19.2 g and nitrogen = 22.1 g. What is the empirical formula? CN
  16. A sample of "monkey mung" was also found at the same time and analyzed. It was found to contain the following element amounts: Mg = 8.062 g and O = 3.99 x 1023 atoms and a molecular molar mass of 450 g/mol. Find the molecular formula. Mg8O16

17.  In the Star Trek series, Mr. Data determined that a mineral sample contained 4.5 g of cesium and 10.7 g of iodine. The molar mass of this sample was determined to be 2701 g/mol. What was the molecular formula of Mr. Data’s sample? Cs6I15

Percent Composition

  1. Find the percent composition of each element in a compound that is 15.62 g nitrogen (55.47%) and 12.54 g of carbon (44.53%).
  2. Find the percent composition of a compound that is 10.12 g aluminum (36.08%) and 17.93 g of sulphur (63.92%).
  3. Calculate the percent by mass of carbon in glucose. 39.99%
  4. Calculate the percent by mass of copper in copper (II) bromide. Cu = 28.45%
  5. Calculate the percent composition of each element in K3N. K = 89.33% and N = 10.67%
  6. Calculate the percentage composition of each element in Al2(SO4)3. Al = 15.77%, S = 28.11%, and O = 56.12%
  7. Find the percent composition of each element in a compound made of 12.5 g barium (33.34%), 16.44 g oxygen (43.85%), and 8.551 g carbon (22.81%).
  8. Find the percent composition of each element in a compound made of 37.5 g iron (51.84%), 8.4 g chlorine (11.61%), and 26.44 g oxygen (36.55%).