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Molar ratio

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    I solved the question algebraically but the method outlined in the mark scheme, which uses a molar ratio, seems much simpler
    However, i dont understand it.
    How would you answer this question?
    Thanks
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    I would do it algebraically

    The other way to do it is to say 16.3% by mass is 16.3/18 and 83.7/460.5 (the mass compound without water)

    gives ratios 0.9055 and 0.1817, division by the smallest => x = 5

    it's very much like the question 'a hydrocarbon is 53.5% carbon, 9% hydrogen the remainer oxygen calculate the empirical formula' except you're dividing by molecules rather than atoms :smile:

    edit: typo!
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    (Original post by EierVonSatan)
    I would do it algebraically

    The other way to do it is to say 16.3% by mass is 16.3/18 and 83.7/460.5 (the mass compound without water)

    gives ratios 0.9055 and 0.1817, division by the smallest => x = 5

    it's very much like the question 'a hydrocarbon is 53.5% carbon, 9% hydrogen the remainer oxygen calculate the empirical formula' except you're dividing by molecules rather than atoms :smile:

    edit: typo!

    Ah. The 'other way' method is assuming that you have 100g of the chemical right?

    So then n =m/Mr can be applied, giving you the molar ratio.
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    (Original post by sonic23)
    Ah. The 'other way' method is assuming that you have 100g of the chemical right?

    So then n =m/Mr can be applied, giving you the molar ratio.
    No you don't need to assume a certain mass - you have the percentages.

    Methane is 75% carbon by mass, 25% hydrogen

    75/12 = 6.25 and 25/1 = 25

    25/6.25 = 4

    CH4

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Updated: June 14, 2009
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