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Percent Composition and Empirical Formulas

Percent Composition and Empirical Formulas. 10.4. 1)What percentage of gum is sucrose, C 12 H 22 O 11 ? 2)Calculate the Percent Composition for sucrose ? (% C %H %O).

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Percent Composition and Empirical Formulas

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  1. Percent Composition and Empirical Formulas 10.4

  2. 1)What percentage of gum is sucrose, C12H22O11? 2)Calculate the Percent Composition for sucrose ? (%C %H %O)

  3. It is an analytical chemists job to identify the elements a compound contains and determine their percent’s by mass. Gravimetric and volumetric mass analyses are experimental procedures based on the measurements of mass for solids, liquids, respectively. The percent by mass of each element in a compound is called the percent composition. Molar mass of carbon from formula Molar mass of compound from its formula The percent's of each element will add up to 100% CHECK YOUR ANSWER:

  4. When a compound’s percent composition is known, its formula can be calculated. First determine the smallest whole number ratio of the moles of elements in the compound. This ratio gives the subscripts in the empirical formula. The empirical formula for a compound is the formula with the smallest whole-number mole ratio of elements. The empirical formula may or may not be the same as the molecular formula. If the two formulas are different, the molecular formula will be a simple multiple of the empirical formula. If the formula is both the molecular and the empirical formula, it cannot be reduced. The empirical formula for hydrogen peroxide is HO; the molecular formula is H2O2. (In both formulas, the ratio of oxygen to hydrogen is 1:1) The empirical and molecular formula for a molecule is C6H14O3PF

  5. Divide by smallest number of moles X 2 = 14 Empirical Formula C14H18N2O5 X 2 = 18 X 2 = 2 X 2 = 5 To make the 2.5 a small whole number, multiply all of these by 2. The answers will be the subscripts in the empirical formula.

  6. If starting with percent composition, just change the % to grams. Then change grams to moles Divide by smallest moles

  7. Substances with distinctly different properties can have the same percent composition and the same empirical formula. To identify a new compound, a chemist determines the molecular formula, which specifies the actual number of atoms of each element in one molecule or formula unit of the substance. Acetylene, C2H2, has the same percent composition and the same empirical formula as benzene, CH. Yet chemically and structurally, acetylene and benzene are very different. To determine the molecular formula for a compound, the molar mass of the compound must be determined through experimentation and compared with the mass represented by the empirical formula. Divide actual molar mass by the mass of the empirical formula indicates the integer to multiply the empirical formula by.

  8. You will be given the molecular formula but you might have to first find the empirical formula from percent composition. Empirical formula molar mass (C3H5O2) Use this subscript to multiply all the empirical subscripts by to get the molecular formula (C3H5O2)2 = C6H10O4

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