SOLUTION: 1) How many cubic centimeters of water must be evaporated from 32 cubic centimeters of 4% solution of salt and water to make a solution that is 16% salt? 2) How much pure silver

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Question 1011699: 1) How many cubic centimeters of water must be evaporated from 32 cubic centimeters of 4% solution of salt and water to make a solution that is 16% salt?
2) How much pure silver must be added to 80 grams of fine silver (an alloy of 90% silver) to obtain a sterling silver (an alloy that is 92.5% silver)?
3) A solution of water and alcohol is 80% alcohol. How much alcohol must be added to 50 gallons of this solution to make it 90% alcohol?
Thanks in advance!

Found 3 solutions by josgarithmetic, addingup, ikleyn:
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
(1)
w, amount of volume to evaporate for removal;
Amount of salt stays the same but amount of solution becomes less as result of removal of some w water.
32%2A4%2F%2832-w%29=16
-
16%2832-w%29=32%2A4
16%2A32-16w=32%2A4
-16w=32%2A4-16%2A32
16w=16%2A32-32%2A4
w=32-2%2A4
highlight%28w=24%29


(2) and (3), learn this:Two part mixture, one material quantity known, the other unknown

Answer by addingup(3677) About Me  (Show Source):
You can put this solution on YOUR website!
Let's call the final number of gallons x. So we want x number of gallons at 90%, we want .90x. And we have 50 gallon at 80%, we have .8*50. Lastly there is the amount we will add to the 50 gallon of 80% to make x gallon of 90%. This amount is 100% alcohol, so it is 1 and 1*x= x. And the quantity of it is x-50:
------------------------------------
.80*50+x-50= .9x
40+x-50= .9x
-10= -.1x Divide both sides by -.1:
x= 100 You have to add 100 gallon of pure alcohol to the 50 gal of 80% to get the solution to 90% concentration.












Answer by ikleyn(52803) About Me  (Show Source):
You can put this solution on YOUR website!
.
For  #1  see the lesson  Mixture problems,  Problem 2;

for  #3  see the Problem 5  of the same lesson.