# Molecular Formula Percent Composition The percent by mass

Molecular Formula

Percent Composition The percent by mass of each element in a compound

To find percent composition, take molar mass of element divided by molar mass of compound and multiply by 100.

What is the percent composition of H in water. (2. 02 g H ÷ 18. 02 g water) X 100 = 11. 2% H

What is the percent composition of O in Glucose (C 6 H 12 O 6). (96 g O ÷ 180. 18 g Glucose) X 100 = 53. 28% O

Empirical Formula The formula of a compound with the smallest whole number mole ration of the elements.

To find empirical formula, take the grams of each element and convert to moles by dividing each element by their molar mass. Then take each mole and divided by the smallest mole. This gives you the subscript for each empirical formula.

What is the empirical formula with 40. 05 g S and 59. 95 g O. 40. 05 g S ÷ 32. 07 g/mol S = 1. 249 mol S 59. 95 g. O÷ 16 g/mol O=3. 747 mol O 1. 249 mol S/1. 249 = 1 mol S 3. 747 mol O/1. 249 = 3 mol O SO 3

What is the empirical formula with 35. 98 g Al and 64. 02 g S÷ 32. 07 g/mol. S=1. 99 mol. S 35. 98 g. Al÷ 26. 98 g/mol. Al=1. 33 mol Al 1. 33 mol Al/1. 33 = 1 mol Al 1. 99 mol S/1. 33 = 1. 5 mol S Al 2 S 3

Molecular Formula It specifies the actual number of atoms of each element in one molecule or formula unit of the substance.

To find the molecular formula, take the experimental mass and divided by the mass of the empirical formula. Take this ratio and multiply by empirical formula to find molecular formula.

What is the molecular formula of a compound with empirical formula of CH and exp. mass of 26. 04 g/mol ÷ 13. 02 g/mol = 2 C 2 H 2

What is the molecular formula of a compound with empirical formula of CH and exp. mass of 78. 12 g/mol ÷ 13. 02 g/mol = 6 C 6 H 6

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