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Warm-Up

Warm-Up. Write the formulas that go with the following names: Tricarbon Pentaoxide Osmium (III) Sulfide Magnesium Nitride Dinitrogen Tetraoxide. Chemistry: Empirical and Molecular Formulas. Unit Five, Day Six Kimrey 18 October 2012. Empirical Formula and Molecular Formula.

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Warm-Up

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  1. Warm-Up • Write the formulas that go with the following names: • TricarbonPentaoxide • Osmium (III) Sulfide • Magnesium Nitride • DinitrogenTetraoxide

  2. Chemistry:Empirical and Molecular Formulas Unit Five, Day Six Kimrey 18 October 2012

  3. Empirical Formula and Molecular Formula • Empirical formula is the simplest chemical formula • Ex. CH4 • Molecular formula is the chemical formula that can be reduced. • Molecular Formula- the formula for a compound in which the subscripts give the actual number of each element in the formulas it truly exists. • Ex. C2H8

  4. Notice two things: 1. The molecular formula and the empirical formula can be identical. 2. You scale up from the empirical formula to the molecular formula by a whole number factor.

  5. Calculating the empirical formula from the percent composition • Steps • Assume the percent = grams. • Convert each amount of grams to moles. • Divide each number of moles by the smallest number of moles. • If all the numbers are not whole numbers, multiple everything by a number that will get you a whole number. (This may take a few tries!) • The whole numbers become subscripts in the formula.

  6. Percent to mass • Mass to mole • Divide by small • Multiply ‘til whole

  7. Example • A compound is 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. What is the empirical formula?

  8. Example 2 • A compound is 40.0% Carbon; 6.71% Hydrogen; 53.29% Oxygen. What is its empirical formula?

  9. Practice • 89.94% C; the rest is H • 56.34% P; 43.66% O   • 43.64% P; 56.36% O   • 40.9% C; 4.58% H; 54.5% O  

  10. Now, finding the molecular formula • Find the empirical formula • Calculate the molar mass (formula mass) • Divide the given mass of the substance by the molar mass • Multiply each subscript of the empirical formula by the answer to #3

  11. Example • You have 56.106 grams of a substance with an empirical formula of CH2. What is the molecular formula?

  12. CuSO4 ● 5H2O • MgSO4 ● 7H2O • SnCl2 ● 2H2O • Na2CO3 ● 10H2O

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