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Empirical Formula

Empirical Formula. 9/21/10. empirical formula = the simplest (most reduced) form of a substance’s formula. example = CH 2 O vs. C 6 H 12 O 6 . CH 2 O is the empirical formula of C 6 H 12 O 6 (divide by 6).

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Empirical Formula

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  1. Empirical Formula 9/21/10

  2. empirical formula = the simplest (most reduced) form of a substance’s formula. example = CH2O vs. C6H12O6. CH2O is the empirical formula of C6H12O6 (divide by 6). C6H12O6is called glucose. This is a molecular formula (it’s unreduced). CH2O is called formaldehyde. This is both the empirical reduction of the glucose formula and formaldehyde’s molecular formula. are glucose and formaldehyde the same? NO! They are completely different substances. However, their empirical formulas just happen to be the same. empirical formula calculations are used to determine the formula of unknown substances from given information, such as the percent composition. how do you calculate the empirical formula of a compound?

  3. how do you calculate the empirical formula of a compound? convert percentages to masses. How? sometimes you will be given percentages to start your problem (see Ex1 below). If this is the case, just take off the % signs and write “g” instead. other times, masses will already be provided for you (see Ex2 below). If so, use these as is. If a total weight is given, subtract as necessary. convert masses (g) to moles (mol). How? Use a conversiontable! Put the weight of your element (in g) on the bottom, 1 mol of your element on top. Leave at least 5 digits in the answers to these conversions. divide all the mole amounts by the smallest one you have. This will “round out” your numbers to either whole numbers or nice, recognizable fractions. Remember: 1/2 = 0.5, 1/3 = 0.33, 2/3 = 0.67, 1/4 = 0.25, 3/4 = 0.75 Even if it’s not exactly equal to the fractions above, it just has to be close.

  4. multiplyall the mole amounts until they are whole. If you get all whole numbers in step 3, then step 4 is unnecessary. If you get a fraction, then multiply all the mole amounts by the denominator of the fraction to make all the numbers whole again. just gather up the whole numbers and write your formula! (If it’s ionic, make it “look ionic” with parentheses if necessary.) Ex1: A compound is 66.04% C, 4.63% H, and 29.33% O. What is its empirical formula? ______ g C 1 mol C = mol C = __ mol C = __ mol C g C _____ g H 1 mol H = mol H = ___ mol H __ = __ mol H g H ______ g O 1 mol O = mol O = __ mol O = __ mol O g O

  5. Ex2: What is the empirical formula of a compound if a 249.15g sample of it contains 132.02g Sn, 45.95 g P, and the rest is oxygen? ________ g T.W. − ________ g Sn − ________ g P = ________ g O ______ g Sn 1 mol Sn = mol Sn = ___ mol Sn = __ mol Sn g Sn ______ g P 1 mol P = mol P = ___ mol P __ = __ mol P g P ______ g O 1 mol O = mol O = __ mol O = __ mol O g O

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