CHRIS25 - 15-3-2014 at 09:42
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.
barley81 - 15-3-2014 at 09:49
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]
Nickdul - 15-3-2014 at 10:00
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]
blogfast25 - 15-3-2014 at 10:21
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]
Nickdul - 15-3-2014 at 10:35
Unless those 40% are molar fraction, bu then it doesn't make sense, as at room temperature it will be supersaturated.
CHRIS25 - 15-3-2014 at 10:35
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]