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It says that the mass of Carbon and Hydrogen are 8:45. We are talking about an alkane here. General formula is CnH2n+2. What is the particular formula?

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Could you be a bit clearer here? I'll reopen when you elaborate/clarify your question and show what you have tried. –  ManishEarth Jan 24 '13 at 7:44
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closed as off topic by ManishEarth Jan 24 '13 at 7:44

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1 Answer

I presume that you mean the ratio by mass of hydrogen to carbon is 8:45. Depending on how many significant figures you select for your carbon and hydrogen masses, as well as the tolerable degree of error in your calculation, you may have several reasonable answers. If we take the mass of one mole of carbon to be 12g, and one mole of hydrogen to be 1g, then the following equality should hold:

$$ 12n/(2n+2) = 45/8 $$

This follows naturally from the general formula for alkanes. Solving the equation, we find $n = 15$, yielding the chemical formula C15H32.

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