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Citric acid, the compound responsible for the sour taste of lemons, has the following elemental composition: C{\rm C}, 37.51%\%; H{\rm H}, 4.20%\%; O{\rm O}, 58.29%\%.Calculate the empirical formula of citric acid

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2 answers
  1. Take a 100 g sample. This gives you
    37.51g C.
    58.29g O
    4.20g H.
    Convert to mols.
    mols = grams/molar mass

    37.51/12 = approx 3.13
    58.29/16 = approx 3.64
    4.20/1 = approx 4.20

    Now find the ratio of the elements to each other with the smallest whole number being 1.00. The easy way to do that is to divide all of the numbers by the smallest value; in this case that is 3.13.
    C = 3.13/3.13 = 1.000
    O = 3.64/3.13 = 1.16
    H = 4.20/3.13 = 1.34

    You may not round these numbers to whole numbers. What you do is multiply each by a whole number, startinhg with 2 and progressing by integers until you get a set of whole number.
    by 2 gives 2:2.32:2.68
    by 3 gives 3:3.48:4 and that tells you that by multiplying by 6 that 3.5 will become a whole number so
    by 6 gives 6:7:8 so the empirical formula is C6H8O7

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  2. That’s exactly what I got

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