||[Jun. 29th, 2011|09:29 pm]
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.
A. 10 mL formic acid + 90 mL H20
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.
I'm not sure if this is right, but here is my instinct:
M1V1 = M2V2
(0.88)(x) = (0.1)(1L)
Yeah, you need the (M1)(V1)=(M2)(V2)
(.88)(x)=(.10)(whatever you want your final volume to be)
Then you add x amount of the formic acid to (final volume - x) amount of water.
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. =(
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.)
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.
Neither A, no B.
It's better to calculate so.
100 g 10 % solution contain 10 g of acid.
So you are to mix 10/0,88=11,36 g of 88 % acid and 100 g - 11,36 g = 88,64 g of water.
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