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# How do you calculate the molecular formula of a substance which contain 80 percent C and 20 percent H?

Updated: 9/20/2023 Wiki User

12y ago

You can only calculate the empirical formula because you do not have a mass of this compound given. To do the empirical formula assume 100 grams and change percent to grams. Get moles.

80 grams Carbon (1 mole C/12.01 grams) = 6.66 moles C

20 grams hydrogen (1 mole H/1.008 grams) = 19.84 moles H

the smallest becomes 1 in the empirical formula and the other number is divided by it, Thus; H/C

19.84 moles H/6.66 moles C

= 2.9, which we call 3

so,

CH3

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is the empirical formula

To get the molecular formula tour question needed to read; How to calculate molecular formula from such ans such mass of compound with these percentages of elements, Which, of course, your question did not provide.

Then you would have divided that given mass by the mass total of the elements of the empirical formula, got a whole number by which you would have multiplied the numbers of your empirical formula to get molecular formula. Wiki User

12y ago   Earn +20 pts  