Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Seymor-Omnis on March 24, 2004, 04:10:24 PM
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Today we did a lab and the teacher made a mistake...quite a large one in fact ::).
The lab required 20 ml of 20% NaOH. First she read the lab wrong and thought it said 10%. Second she just moved the decimal to create a .1 molar solution.
This was very wrong, and I am wondering why. How do you calculate percent composition? Any help is greatly appreciated.
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There are a lot of ways to calculate it. She was probably doing it by volumes instead of by moles. When I make a 10%HCl solution, its usally 1 part 12M HCl with 9parts water.
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ok...that was very informative...except i did not understand any of it ;D.
Could you explain it again?
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As Mitch mentioned there could be different ways of doing it... you could be talking about moles, mass, or volume.
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fgregpawin.chemicalforums.com%2Fpercentcomposition.gif&hash=dfce9ebf28b14bf1f9d59b7f40ccd717cdd2e5b7)
Because in the end all you get is a ratio, confusion is common. That's why usually, if you're going to talk about concentration using percent composition, by "weight/mole/volume" should be mentioned.