The Mole & Chemical Formulas

# The Mole & Chemical Formulas

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## The Mole & Chemical Formulas

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1. The Mole & Chemical Formulas • A chemical formula represents the ratio of atoms that always exists for that compound • Example: Water – H2O • Always 2 H atoms to 1 O atom

2. The Mole & Chemical Formulas • This also means if you had a mole of water… • You would have 2 moles of Hydrogen atoms • And 1 mole of Oxygen atoms

3. Empirical Formula • This is the simplest ratio of atoms in a chemical formula. • Example: • Glucose, a sugar, has the molecular formula C6H12O6 • The empirical formula is CH2O

4. Empirical Formula • Example: • A chemical has 80.0% C atoms and 20.0% H atoms. What is the empirical formula of the compound? • Use the %’s as masses to find moles…

5. Empirical Formula 80.0 g C 1 mol C = 6.67 mol C 12.0 g C 20.0 g H 1 mol H = 20.0 mol H 1.0 g H

6. Empirical Formula • Use the moles to determine the ratio: This is the Empirical Formula! 6.67 mol Carbon: = 1 6.67 mol C H3 20.0 mol Hydrogen: = 3 6.67 mol

7. Molecular Formula • This gives the actual number of atoms for each element in a compound. • Example: • If the molar mass of the “CH3” compound from the previous problem is 30.0 g/mol, what is the molecular formula?

8. Molecular Formula • Empirical formula mass for CH3 is 15.0 g/mol • Then find the ratio of molar to empirical mass. 30.0 g/mol (molecular) = 2.00 15.0 g/mol (empirical)

9. Molecular Formula • Multiply the empirical formula by your new ratio: • C(1x2)H(3x2) = C2H6 (molecular formula)

10. Molecular Formula • Example: • A chemical is 48.4% C atoms, 8.12% H atoms and the rest is Oxygen. If the molecular mass is 222 g/mol, find the molecular formula. • First find empirical formula…

11. Molecular Formula 48.4 g C 1 mol C = 4.03 mol C 12.0 g C 8.12 g H 1 mol H = 8.12 mol H 1.0 g H 43.5 g O 1 mol O = 2.72 mol O 16.0 g O

12. Molecular Formula 4.03 mol x 2 = 3 Carbon: = 1.48 C3 H6 O2 2.72 mol 8.12 mol x 2 = 6 Hydrogen: = 2.99 2.72 mol 2.72 mol x 2 = 2 Oxygen: = 1.00 2.72 mol

13. Molecular Formula 222 g/mol (molecular) = 3.00 74.0 g/mol (empirical) C3x3 H6x3 O2x3 C9H18O6 Molecular Formula!