CHRIS25
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Help needed with maths please.
Yes yes, I know, but I simply can not compute my brain with maths, and I find it infuriating.
I want to make a 5% concentration of acetic acid from a 40% concentration into 1 litre. Yes stupid isn't it, but I simply can not work it out - I
have 20 pages in two chapters of two chemistry books that deal with everything moles and mass and more, but not one clue on how to work this one out.
I reasoned that 100% acetic is 17.4 mol. Therefore 40% of this would be 6.96 mol. 5% of this would be 0.87 mol. But I don't have the concentrated
so taking 5% of my 40% would be giving me around 2% strength because there is 60% water. So juggling maths and logic and getting all screwed up
because I can not work out the maths to do this accurately I humbly admit my stupidity and ask for the formula please.
I did reason out that 5/40 x 100/1 = 12.5% and wondered if this was correct. 12.5 ml in 1 litre from the 40% would give me 5% strength I am looking
for.
Thankyou.
[Edited on 15-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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Fossil
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Give this a try
http://www.sigmaaldrich.com/chemistry/stockroom-reagents/lea...
If you scroll down a little, the formula will be listed as well as a step by step walkthrough.
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CHRIS25
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Well, thankyou fossil, that site is a great site for me. Much appreciated.
But how do I calculate the percentage of my result? When working with concentrated solutions that is not a problem, but after calculating 1 mole from
40% on that site's calculator I find my maths was spot on regarding moles, but can not figure out percentages when the solutions are already not
concentrated.
The 1 mole is 143 mL in a 1000 mL water. Is this 14.3%?
[Edited on 15-7-2012 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
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|
|
kavu
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No need to bother with molarities. It can be solved with the good old c1V1 = c2V2. Percentages are directly proportional with volumes. You want to
have 1 L of 5% acetic acid, so V1 = 1L and c1 = 5%. V2 is the volume you need of the 40% solution and c2 = 40%. Solve for V2 and plug in the values:
V2 = c1/c2 * V1 = 0.125 * 1 L = 125 mL
So measure out 125 mL of 40% solution and dilute it to to 1 liters.
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Funkerman23
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Quote: Originally posted by kavu  | No need to bother with molarities. It can be solved with the good old c1V1 = c2V2. Percentages are directly proportional with volumes. You want to
have 1 L of 5% acetic acid, so V1 = 1L and c1 = 5%. V2 is the volume you need of the 40% solution and c2 = 40%. Solve for V2 and plug in the values:
V2 = c1/c2 * V1 = 0.125 * 1 L = 125 mL
So measure out 125 mL of 40% solution and dilute it to to 1 liters. |
That from Vogel's bychance?
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kavu
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Nope, that's found in any introductory chemistry textbook that has ever existed! It should also be found in every chemist's head.
[Edited on 15-7-2012 by kavu]
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CHRIS25
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| Quote: Originally posted by kavu | No need to bother with molarities. It can be solved with the good old c1V1 = c2V2. Percentages are directly proportional with volumes. You want to
have 1 L of 5% acetic acid, so V1 = 1L and c1 = 5%. V2 is the volume you need of the 40% solution and c2 = 40%. Solve for V2 and plug in the values:
V2 = c1/c2 * V1 = 0.125 * 1 L = 125 mL
So measure out 125 mL of 40% solution and dilute it to to 1 liters. |
Thanks, great help. Though it would have been easier if I had simply seen the equation 5/40 x 1000/1. Now That I can comprehend, that makes sense.
Going through the chemistry section I see this formula, but yeh, they complicate matters by throwing out c's and v's c1's and v2's without a simple
straight-forward explanation of the mathematical principle at work. That annoys me, had I have seen just good old fashioned figures written in a good
old fashioned way then I would have grasped it and no need to post on the forum.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
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