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### Topic: Percent Composition Question  (Read 10441 times)

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#### Seymor-Omnis

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##### Percent Composition Question
« on: March 24, 2004, 04:10:24 PM »
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.

#### Mitch

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##### Re:Percent Composition Question
« Reply #1 on: March 24, 2004, 04:27:33 PM »
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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#### Seymor-Omnis

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##### Re:Percent Composition Question
« Reply #2 on: March 24, 2004, 06:15:05 PM »
ok...that was very informative...except i did not understand any of it  .

Could you explain it again?

#### gregpawin

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##### Re:Percent Composition Question
« Reply #3 on: March 24, 2004, 08:10:41 PM »
As Mitch mentioned there could be different ways of doing it... you could be talking about moles, mass, or volume.

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.
« Last Edit: March 24, 2004, 08:18:04 PM by gregpawin »
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