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Homework Help: Weight combination by percent

  1. May 9, 2006 #1
    How on earth do you do this?

    What percent by weight of Na2S2O3 is Sodium (Na)? (Na, 23; S, 32; 0, 16)

    Okay that looks confusing but. The "Na2S2O3" isn't suppose to be spelled like that. It's Na (then a 2 that is haflway beneath the number) And then you repeat with S (lower 2), O and lower 3. It's hard to explaina and i don't know what it's called.

    But how do i solve this?
  2. jcsd
  3. May 9, 2006 #2
    I take it that the text in parentheses refers to the masses of each of the elements in the compound.

    A good start would be to calculate the total mass of the compound, keeping in mind the fact that there are different numbers of each element in the compound (i.e. there are 2 sodium ions, etc.).
  4. May 18, 2006 #3
    How do i calculate it though? I don't understand the 2,2,&3 that belong to Na,S,&O
  5. May 18, 2006 #4


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    Gold Member

    Na2S2O3 means that the given molecule/unit (Sodium thiosulfate) is composed of two atoms of Na, two atoms of S, and three atoms of O.

    By looking at a periodic table (or the values that are given to you) you can realize that one mole of Na has a mass of 23 grams. One mole of S has a mass of 32 grams. One mole of O has a mass of 16 grams.
    Last edited: May 18, 2006
  6. May 19, 2006 #5
    I figured out it's 29%
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