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Law of constant composition

  1. Mar 23, 2016 #1
    It states "a pure chemical compound is always made up of the same elements combined together in the same fixed ratio by mass."
    But how can a compound have the same elements ? For example,let's take ethanol,it is composed of hydrogen,carbon and oxygen.So three elements and not the same element.
  2. jcsd
  3. Mar 23, 2016 #2


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    Dimethyl ether and ethanol are not the same compound, and composed of the same elements in the same ratios. You cannot be picking semantic nits about use of the word "same."
  4. Mar 24, 2016 #3


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    If I were to tell you that my siblings and I have the same parents, would you say that did not make sense because one is a father and the other a mother?

    By the way, I don't understand why things like the law of constant composition are still taught. Once we understood what a molecule is, the law became trivial and archaic.
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