CHRIS25
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Maths problem
I have a 40% copper acetate solution which I made. In a certain recipe I need 10grams of this copper acetate, Cu(CH3COO)2. If I knew how to find out
what the molarity of a concentrated copper acetate solution should be, then I could work out how to turn the 40% that I have into the number of grams
per litre. Could someone help me please?
188g/mol x Molarity of concentrated solution.
This represents 100%
Thus, 40% of the total grams per liter would tell me how many grams my concentration is
then 10% of this solution is what I need.
Hope this is correct.
‘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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barley81
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Actually, you don't need molarity for this calculation. If you want 10g of copper acetate, and your solution has 40% of copper acetate by
mass, you should weigh 25g of solution because the density of the solution is not known. If the solution is 40% w/v (40g
copper acetate in 100mL solution), then you need to measure out 25mL of solution.
Hope this helped!
EDIT: A 40% copper acetate solution doesn't exist. Do you mean 0.4 M copper acetate? In that case, in order to get the equivalent of 10g copper
acetate hydrate, you need 125mL.
[Edited on 15-3-2014 by barley81]
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Nickdul
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First of all, is your copper acetate solution 40% as wt/wt, wt/vol, or molar fraction? Whatever the case, it is simple algebra to calculate what
volume(or weight/mass) of solution you need to use.
For weight fraction, you have a solution that contains 40g of copper acetate per 100g of solution. Of that, you need to use 25g.
For wt/volume fraction, you'd have 40g of copper acetate per 100ml of solution. Respectively, you need 25ml.
For mole fraction, it is easiest to convert to wt/wt. Since you have a concentration that is expressed as the molar mass ratio of compound to
compound+solvent, and assuming your solution is in water, the calculation becomes 40%X181.6g/mol over 40%X181.6g/mol + 18(approx mol mass of
H2O)*60%(the remaining molar fraction for water)
Then, your 40% molar fraction solution of copper acetate is by weight 87%. Now as wikipedia suggests solubility of 72g/L, I suspect you percent
solution is either by wt/wt of wt/vol.
Now, I could be wrong in my reasoning, so please do correct me in that case 
[Edited on 15-3-2014 by Nickdul]
[Edited on 15-3-2014 by Nickdul]
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blogfast25
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Acc. wiki:
"monohydrate:
7.2 g/100 mL (cold water)
20 g/100 mL (hot water"
All a long way from 40 %...
[Edited on 15-3-2014 by blogfast25]
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Nickdul
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Unless those 40% are molar fraction, bu then it doesn't make sense, as at room temperature it will be supersaturated.
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CHRIS25
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Thankyou for the maths demonstrations, this all helps. I'm a slow tortoise in thinking mathematically, so in no position to correct. However all
this explanation is of great help thankyou. blogfast - always look at wiki and other references before posting, it seems then that my solution can
not be 40%, the maximum concentration of any copper acetate solution can not be more than 20%, i assume this is what you are pointing out to me?
edit. Unfortunately I made the solution last year using copper and acetic acid and have no idea the amount of copper I used. I wrote 40% for a
reason, but that reason is now forgotten.
[Edited on 15-3-2014 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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