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Empiricial vs. Molecular Formulas

Empiricial vs. Molecular Formulas. A molecule that contains the smallest whole number ratio of elements within the compounds CH 2 O The subscripts CANNOT be reduced. A molecule that shows the actual number of elements within the compound C 2 H 4 O 2 The subscripts CAN be reduced.

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Empiricial vs. Molecular Formulas

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  1. Empiricial vs. Molecular Formulas • A molecule that contains the smallest whole number ratio of elements within the compounds • CH2O • The subscripts CANNOT be reduced • A molecule that shows the actual number of elements within the compound • C2H4O2 • The subscripts CAN be reduced

  2. Calculating Empirical Formula Divide answers from #2 by the SMALLEST answer to get the ratio between the elements 1.407 mol / 0.7078 mol = 1.987  2 0.7078 mol/ 0.7078 mol = 1 2.8119 mol/ 0.7078 mol = 3.97  4 Quantitative analysis shows that a compound contains 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. Find the empirical formula of this compound. 1. Change % to g–change units 32.38% - 32.38 g 22.65% - 22.65 g 44.99% - 44.99 g • Convert g to moles Na: 32.38 g 1 mol = 1.407 mol 23 g S: 22.65 g 1 mol= 0.7078 mol 32 g O: 44.99 g 1 mol= 2.8119 mol 16 g The answers are the subscripts for the elements involved in the compound Na2SO4 – Empiricial

  3. Calculating Molecular Formula • Must know empirical formula first The empirical formula for a compound is P2O5. Experimentation shows that the molar mass of the compound is 283.89 g/mol. What is the compounds molecular formula? Empirical Formula – P2O5 Mass of Empirical F. - (30.97*2) + (16*5) = 141.94 Mass of molecular formula (get from problem) = 283.89= 2 Mass of empirical formula 141.94 This tells me the Molc. F. is 2Xs as larger as the Empi. F. EF*2 = MFP2O5*(2) = P4O10

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