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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.

Warm-Up

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### 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.

### 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.

• 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