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Author: Subject: molarity assistance
gravityzero
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molarity assistance

Really hate to ask this, but I'm trying to avoid further confusion.

If anyone has the time, please verify my results.

I have a synthesis where I am asked to use .20 moles of a 30% Hydrogen peroxide solution.
I think I have the hang of this, but if anyone can comment on my math I'd appreciate it.

I found a mole of pure H2O2 to be 34.0147 grams.

34.0147 * .20 = 6.80294 grams of pure H2O2

So, I assume that 6.80294 grams will equate to 30% of the overall gram weight.
This would mean that the overall weight would be 22.6765 grams.

22.6765 - 6.80294 = 15.8735g H2O or 15.8735ml of H2O

So, from I can determine I would use 22.6765g of a 30% H2O2 solution.

This comprised of:

15.8735 ml H2O
4.69168 ml H2O2
-----------------
20.5652 ml of 30% H2O2
DraconicAcid
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Is it 30% by mass or by volume?

Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
gravityzero
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The scientific journal was not specific
I did my calculations assuming it meant 30% by mass.
DraconicAcid
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Merck index says that 30% hydrogen peroxide is generally by weight (by which they mean mass), so your calculations are correct. You are, however, being far too precise, since 30% hydrogen peroxide often varies between 29% and 32%. Call it 21 mL.

Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
gravityzero
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Thanks DraconicAcid

I appreciate the help.
I find it difficult to work with Hydrogen peroxide, mainly for the reason mentioned.

I find it difficult to know the percentage of the H2O2, especially after it has been sitting in the fridge a while.

I've attempted to determine percent solution based on solution weight.
I've also tried titrating using MnO2.
I get different results using both and result to pretty much guessing.
essbee
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Well done Drac'.....my 'friend' asked a similarly basic question and was zapped all the way to detritus by the almighty bfesser and told that he would not be doing his homework for him.
Not to insult furher bfesser...but he does seem to have some control issues which seem at odds with his 'position' as a moderator.

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