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



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


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.

[User Picture]From: surrey_sucks
2011-06-30 04:41 am (UTC)
I'm not sure if this is right, but here is my instinct:

M1V1 = M2V2

(0.88)(x) = (0.1)(1L)
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[User Picture]From: smokeline
2011-06-30 05:20 am (UTC)
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.
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[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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[User Picture]From: superhimik
2011-07-01 10:10 am (UTC)
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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