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# NIU CHEM 210 - Calculating Mass/Percent , Empirical Formulas and an Introduction to Isomers

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CHEM 210 1nd Edition Lecture 11 Outline of Last Lecture I. Converting Using MolesOutline of Current Lecture II. Calculating Mass/PercentIII. Empirical FormulaIV. IsomersCurrent LectureCalculating the mass/percent of a compound is simply multiplying the amount of each element to its molar mass and adding them up together.For example,Glucose is written with the following formula, C6H12O6. To find mass/percent, you must first find the molar mass of the compound. You do this by multiplying the total number of each of the elements, to their molar mass, which can be found using a periodic table.C= (6 X 12.01) + H= (12 X 1.01) + O= (6 X 16.00)= 72.06 + 12.12 + 96 = 180.18 g/molNow to found the percent of each element, you take the molar mass, divide by the total compound mass and multiply by 100.%C = 72.06 / 180.18 X 100 = 39.99%%H = 12.12 / 180.18 X 100 = 6.727%%O = 96.00 / 180.18 = 53.28%These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.An empirical formula is the simplest formula for a compound. It is represented as the simplest whole number ratio.For example, 2.82 g Na, 4.35 g Cl, 7.83 g OYou first have to convert from grams to moles by dividing the grams of each element given to you, by the molar mass. Na = 2.82 / 22.99 = 0.123Cl = 4.35 / 35.45 = 0.123O = 7.83 / 16.00 = 0.489Then you divide by the smallest number of moles, which in this case is 0.123Na = 0.123 / 0.123 = 1Cl = 0.123 / 0.123 = 1O = 0.489 / 0.123 = 4The result is NaClO4, which is sodium perchlorateIsomers are compounds that have the same molecular formula but different structures.An example is ethanol and dimethyl ether, which both have the molecular formula C2H6O, but structurally look

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