Empirical Formula Examples with Solutions

🧪 Quick Study Guide

• ⚛️ The empirical formula represents the simplest whole number ratio of atoms in a compound.
• 📝 To determine the empirical formula:
  1. Convert percentage composition to grams.
  2. Convert grams to moles using molar mass.
  3. Divide each mole value by the smallest mole value to get the simplest ratio.
  4. If necessary, multiply by an integer to get whole numbers.
• ➗ Remember, the empirical formula is NOT the same as the molecular formula. The molecular formula is a multiple of the empirical formula.
• ⚖️ Molar mass is a crucial conversion factor. Make sure you know how to calculate it!
• 💡 If you end up with ratios like 1:1.5, multiply by 2 to get whole numbers (2:3).

✍️ Practice Quiz

1. What is the empirical formula of a compound containing 80% carbon and 20% hydrogen?
   1. $CH_2$
   2. $CH_3$
   3. $CH_4$
   4. $C_2H_5$
2. A compound contains 40% carbon, 6.7% hydrogen, and 53.3% oxygen. What is its empirical formula?
   1. $CH_2O$
   2. $C_2H_4O$
   3. $CHO_2$
   4. $C_2H_2O_2$
3. What is the empirical formula of a compound with the molecular formula $C_6H_{12}O_6$?
   1. $C_6H_{12}O_6$
   2. $C_3H_6O_3$
   3. $CH_2O$
   4. $C_2H_4O_2$
4. A compound is found to have 60% oxygen and 40% sulfur by weight. What is the empirical formula of this compound?
   1. $SO$
   2. $SO_2$
   3. $S_2O_3$
   4. $SO_3$
5. A compound contains 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. What is its empirical formula?
   1. $NaSO_4$
   2. $Na_2SO_3$
   3. $NaSO_3$
   4. $Na_2SO_4$
6. What is the empirical formula of a compound that contains 1.01 g of H and 35.45 g of Cl?
   1. $HCl_2$
   2. $H_2Cl$
   3. $HCl$
   4. $H_3Cl$
7. A compound contains 62.1% C, 10.3% H, and 27.6% O. What is its empirical formula?
   1. $C_3H_6O$
   2. $C_6H_{12}O_2$
   3. $C_3H_5O$
   4. $C_6H_{10}O$