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**Chapter 11 Empirical and Molecular Formulas**

Chemistry Chapter 11 Empirical and Molecular Formulas

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Empirical Formulas The simplest whole number ratio of the elements in a compound (not necessarily the actual formula for a compound) Ex H2O2 = HO H2O= H2O C6H12 = CH2 C8H16 = CH2 Can be calculated from % composition

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**Empirical Formula (Cheat Sheet)**

1. % composition (if = 100%) converts to mass Convert from mass to moles Calculate simplest ratio (divide all # mol by the smallest # moles) 3 ½. If not all whole numbers, multiply all by a whole # to create whole #’s 4. Use simplest ratio as subscripts

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Examples 11.2 % Hydrogen and 88.8% Oxygen

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Examples 36.84% N and 63.16% O

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Examples 60% C, 4.44%H, and 35.56% Oxygen

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**Molecular Formula Actual number of moles of each element in a compound**

Need more info than just % comp Need molar mass of the empirical formula Need an experimental mass of the actual compound

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**Molecular Formula (Cheat Sheet)**

Use steps to calculate empirical formula Calculate molar mass of empirical formula The question will give you experimental mass of the compound Experimental mass Empirical form. Molar mass = 5. Multiply subscripts in empirical by your answer (whole number)

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Example A colorless liquid is found to be composed of 46.68% N and 53.32% O and has a molar mass of g/mol. What is the molecular formula?

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