Percent Composition, Empirical Formula, & Molecular Formula Revi

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What is percent composition?

Back

Percent composition is the percentage by mass of each element in a compound, calculated by dividing the mass of each element by the total molar mass of the compound and multiplying by 100.

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How do you calculate the percent composition of water in a hydrate?

Back

To calculate the percent composition of water in a hydrate, divide the mass of the water in the formula by the total molar mass of the hydrate and multiply by 100.

Front

What is an empirical formula?

Back

An empirical formula is the simplest whole-number ratio of atoms of each element in a compound.

Front

How do you determine the empirical formula from percent composition?

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Convert the percentages to grams, then to moles, and find the simplest ratio of moles of each element.

Front

What is a molecular formula?

Back

A molecular formula shows the actual number of atoms of each element in a molecule, which may be a multiple of the empirical formula.

Front

How do you find the molecular formula from the empirical formula?

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To find the molecular formula, divide the molar mass of the compound by the molar mass of the empirical formula, then multiply the subscripts in the empirical formula by this ratio.

Front

What is the molar mass of water (H2O)?

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The molar mass of water (H2O) is 18.0 g/mol.

Front

Calculate the percent composition of oxygen in carbon dioxide (CO2).

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The molar mass of CO2 is 44.01 g/mol. The percent composition of oxygen is (32.00 g/mol / 44.01 g/mol) x 100 = 72.7%.

Front

What is the empirical formula for a compound with 40.05% sulfur and 59.95% oxygen?

Back

The empirical formula is SO3.

Front

If the empirical formula is CH2O and the molar mass is 180.18 g/mol, what is the molecular formula?

Back

The molecular formula is C6H12O6.