Warm-Up

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# Warm-Up - PowerPoint PPT Presentation

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

### Chemistry:Empirical and Molecular Formulas

Unit Five, Day Six

Kimrey

18 October 2012

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
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.
• 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.
Percent to mass
• Mass to mole
• Divide by small
• Multiply ‘til whole
Example
• A compound is 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. What is the empirical formula?
Example 2
• A compound is 40.0% Carbon; 6.71% Hydrogen; 53.29% Oxygen. What is its empirical formula?
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
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
Example
• You have 56.106 grams of a substance with an empirical formula of CH2. What is the molecular formula?
CuSO4 ● 5H2O
• MgSO4 ● 7H2O
• SnCl2 ● 2H2O
• Na2CO3 ● 10H2O