Empirical and Molecular Formulas Composition of Ca CO

% Composition of Ca. CO 3 �Molar Mass of Ca. CO 3 = 100.

The basics �Empirical formula: Simplest formula of a compound, has the lowest whole #

Empirical formulas Write the empirical formulas for the following molecular formulas: P 4 O

How to find empirical formulas from % composition 1. Change the % to grams

Empirical Formula Ex. 1 A compound contains 27. 29% Carbon and 72. 71% Oxygen,

Empirical Formula Ex. 2 A compound contains 25% Potassium, 35% Manganese, and 40% Oxygen,

Empirical Formula Ex. 3 Find the empirical formula of the compound that contains 27.

Determining the molecular formula: 1. Calculate empirical formula 2. Calculate the molar mass of

Example 4 �A compound contains 63. 11 % C, 12. 36 % H, and

Example 5 �If 4. 04 g of N combine with 11. 46 g O

Example 6 �The molar mass of a compound is 92 g/mol. Analysis of a

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Empirical and Molecular Formulas

% Composition of Ca. CO 3 �Molar Mass of Ca. CO 3 = 100. 08 g/mol % Ca = (40. 08 / 100. 08) x 100 = 40% % C = (12. 01/100. 08) x 100 = 12 % % O = (15. 999 x 3)/100. 08 x 100 = 48% Double Checking my answer…. 40+12+48 = 100!

The basics �Empirical formula: Simplest formula of a compound, has the lowest whole # ratio �Reduced version �Usually not even a real substance �Molecular formula: The actual formula of a molecular substance �Both have the same % composition �Sometimes empirical and molecular formula are the same!

Empirical formulas Write the empirical formulas for the following molecular formulas: P 4 O 10 C 6 H 12 O 6 SO 4 N 2 O 4

How to find empirical formulas from % composition 1. Change the % to grams � Assume dealing with a 100. 0 gram sample � If given grams then skip step one 2. For each element convert the # of grams moles 3. Divide all the mole values by the smallest number of moles to get your mole ratios � If needed, multiply ratios to get a whole number Ratios = subscripts in empirical formula

Empirical Formula Ex. 1 A compound contains 27. 29% Carbon and 72. 71% Oxygen, what is the empirical formula?

Empirical Formula Ex. 2 A compound contains 25% Potassium, 35% Manganese, and 40% Oxygen, what is the empirical formula?

Empirical Formula Ex. 3 Find the empirical formula of the compound that contains 27. 36 % Na, 1. 20 % H, 14. 30 % C, and 57. 14 % O Na. HCO 3

Determining the molecular formula: 1. Calculate empirical formula 2. Calculate the molar mass of the empirical formula 3. Calculate the ratio: Molar Mass (given to you) = X Empirical Formula Mass (step 2) 4. Multiply the empirical formulas subscripts by “X” to get the molecular formula

Example 4 �A compound contains 63. 11 % C, 12. 36 % H, and 24. 53 % N. What is its empirical formula? If the molar mass is 114. 2 g/mol, what is the molecular formula?

Example 5 �If 4. 04 g of N combine with 11. 46 g O to produce a compound with a molar mass of 108. 0 g/mol, what is the molecular formula?

Example 6 �The molar mass of a compound is 92 g/mol. Analysis of a sample of the compound indicates that it contains 0. 606 g N and 1. 390 g O. Find its molecular formula.