my hardest chem question - BasilMarket Forum

thread starter chaostheory May 17 2010 + PM | QUOTE | PERMALINK | REPORT

So I have this question for chem. This was the bonus on my test : A .225 gram of an oxohyrdocarbon is burned in excess oxygen, the only yield is carbon dioxide and water. .512 gram Of carbon dioxide is formed and .209 gram of water is formed. What is the empir8cal formula . The gram formula mass is 232 g/mol. What is the molecular formula?

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bloodIsShed 05/17/10 + PM | QUOTE | PERMALINK | REPORT

oxohydrocarbon: oxo - O hydro - H carbon - C First, set up the chemical equation: CxHyOz + O2 --> CO2 + H20 (obviously not balanced) Convert the grams of CO2 to moles of CO2 Once you know the moles of CO2, you know how many C moles there were before the reaction took place. Do the same thing for O and H. It is assumed that there's only enough O2 to react with all of the compound. Now that you have the values for C, H, and O: C - a moles H - b moles O - c moles Divide all by the lowest of the three values (a,b, c), and multiply by an integer to get the lowest integer ratio between the three. (Ex. C - 9 moles, H - 15moles, O-21moles becomes C - 3moles, H - 5 moles, O - 7moles) Write in the form CxHyOz. That's the empirical formula. To find the molecular formula, get the molar mass (in this case, 232g/mol), and divide it by the empirical mass. You should get an integer, or some number close to an integer (in which case, you round up/down) Multiply the x, y, z to that number, and out comes the molecular formula.

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