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Empirical Formulas |
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Chemistry Made Easy With "Professor" Schwartz
Determining Empirical Formulas From Percent Composition Determining percent composition from empirical formulas is quite simple when you follow my steps very carefully. These problems once learned will be your favorites. Follow this problem below and the rest will be a breeze. Example Benzoic acid contains 68.8% carbon, 4.95% hydrogen, and 26.2% oxygen by mass. What is the empirical formula of this compound? 1) Figure out what your formula is. C(carbon) H(hydrogen) O(oxygen), thus CHO
2) Assume the total % of all the elements is equal to 100. 68.8+4.95+26.2=100
3) Divide each percent of element by its molar mass. 68.8/12 = 5.73 4.95/1.01 = 4.90 26.2/16.0 = *1.64
4) Your answer is now in moles. After getting the results of each element, divide the element with the lowest mass by the rest of the elements. 68.8/12.0 = 5.73----5.73/1.64 = 3.5 4.95/1.01 = 4.90----4.90/1.64 = 3 26.2/16.0 = 1.64----1.64/1.64 = 1
5) If all of your answers are not whole numbers multiply them by the same number to make them a whole number. YOU MUST DO IT TO ALL OF THEM 68.8/12.0 = 5.73----5.73/1.64 = 3.5 x 2 = 7 4.95/1.01 = 4.90----4.90/1.64 = 3 x 2 = 6 26.2/16.0 = 1.64----1.64/1.64 = 1 x 2 = 2
6) Now plug these numbers into your formula. C7H6O2
The answer in its entirety is : C 68.8/12.0 = 5.73----5.73/1.64 = 3.5 x 2 = 7 H 4.95/1.01 = 4.90----4.90/1.64 = 3 x 2 = 6 = C7H6O2 O 26.2/16.0 = 1.64----1.64/1.64 = 1 x 2 = 2 Questions 1) A particle of freon contains 9.93% carbon, 56% chlorine, and 31.4% fluorine, what is the empirical formula?
2) A compound consists of 40% calcium, 12% carbon, and 48% oxygen by mass, what is its empirical formula?
3) A compound consists of 85% silver, and
15% fluorine by mass, what is its empirical formula by mass?
4) A compound consists of 50% magnesium, 24% carbon, 16% oxygen, and 10% hydrogen. What is its empirical formula?
5) A compound consists of 75% magnesium, and 25% oxygen by mass. What is its empirical formula?
6) What is the empirical formula of a compound that has 66% calcium and 34% phosphorous?
Answers 1) CCl2F2 2) CaCO3 3) AgF 4) MgC2OH10 5) Mg2O 6) P2Ca3 Please forward all questions, comments and criticisms to Gregory L. Curran. |
