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Empirical Formula by Mass |
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Chemistry Made Easy With "Professor" Schwartz
Determining Molecular Formulas by Mass
The empirical formulas of a compound is the simplest ratio of the elements in that compound. For example Hydrogen Peroxide has the molecular formula of H2O2, it empirical formula is HO. * * This can be found by finding the ratio between two different moles of a certain formula.** Follow these steps to solve all your problems with empirical formulas.
Example A compound has the empirical formula of CH2 and a molecular mass of 42u. Determine its molecular formula.
Step 1 Line up the elements on the side of the page and find their atomic mass.(***Notice there is a subscript of two with hydrogen, two hydrogen's atomic mass must be multiplied by two. This has to be done with all elements a subscript.) C = 12.0 2H = 2.02
Step 2 Add the atomic masses. C = 12.0 2H = 2.02 = 14.0
Step 3 Divide the sum by the mass given. C = 12.0 2H = 2.02 42/14 = 3 = 14
Step 4 Now you must multiply your answers by the number of elements present. C = 12.0 C = 1 x 3 2H = 2.02 = 42/14 = 3 thus your answer is C3H6 = 14.0 H = 2 x 3
Here are some practice problems to try your hand at!!!! Good luck and just remember to follow the steps. 1) Calculate the empirical formula of a compound that contains 1.67g of cerium, Ce, and 4.54g of iodine, I.
2) A sample of two methylpropene contains 0.556g C and 0.0933g H. Determine the empirical formula.
3) A 9.2g sample of a compound is 2.8g nitrogen and and 6.4g oxygen. Find the empirical formula of the compound.
Answers 1) CeI3 2) CH2 3) NO2 For more questions and answers Empirical formulas with percent composition Please forward all questions, comments and criticisms to Gregory L. Curran. |
