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10% solution [Jun. 29th, 2011|09:29 pm]
Chemistry Help

chemistryhelp

[sarah1234567891]
HI

I need to make  10% formic acid   (my formic acid has a 88% purity)


i'm confused as to how to do this. let's use 100 mL to make it easier to calculate.


Do I:

A.  10 mL formic acid + 90 mL H20

or

B. 10 mL formic + 100 mL H2O?


When do I use A and when do I use B to calculate?



I was making a 0.1% Formic acid in water 1 L solution, I used calculation B to make the solution.  1.14 mL of formic acid + 1000mL H2O.
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Comments:
[User Picture]From: sarah1234567891
2011-06-30 07:14 am (UTC)
Can you explain this to me?

I'm following a procedure and they make a 4.25% H3PO4 in buffer

the recipe they use is:

4.25 mL of H3PO4 ( purity 86% density 1.685) + 100 mL buffer

4.25 / 104.25 is not 4.25%

M1V1 = M2V2 doesnt work here. =(
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[User Picture]From: smokeline
2011-06-30 04:22 pm (UTC)
I guess it depends on whether the purity is by volume, concentration, or weight. The calculations would be different based on that. (And also whether the 4.25% solution is 4.25% by volume, concentration, or weight.)
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[User Picture]From: grenjelybean
2011-06-30 08:01 pm (UTC)
Volume percent is defined as volume of solute over volume of solvent. so 4.25mL/100mL is 4.25%. But then it's not really because it's not 100% pure H3PO4. So, I don't know.

Concentration can be quite tricky sometimes if you miss exactly how it's being expressed.
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