SOLUTION: Dmitri needs 7 liters of a 24% solution of sulfuric acid for a research project in molecular biology. He has two supplies of sulfuric acid solution: one is an unlimited supply of 2

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Question 621572: Dmitri needs 7 liters of a 24% solution of sulfuric acid for a research project in molecular biology. He has two supplies of sulfuric acid solution: one is an unlimited supply of 28% solution and the other an unlimited supply of the 14% solution. How many liters of each solution should Dmitri use?
Answer by dragonwalker(73) About Me  (Show Source):
You can put this solution on YOUR website!
First look at how each solution is different from the required concentration.
The 28% is +4% from the required 24%
The 14% id -10% from the required 24%
So the effect of the 28% is only 4/10 of the effect of the 14%
so you need 10/4 times more of the 28% than the 14%
So let us call the volume of the 14% 'x'
So the volume of the 28% is10x/4
As the total volume needed is 7 liters this may be written:
x + 10x/4 = 7
solve for x:
(multiply all by 4 to remove denominator of 10x/4)
4x + 10x = 28
14x = 28
x = 28/14
x = 2
So the volume of the 14% is 2 litres and therefore the amount of 28% is 10/4 x 2
=5
Check:
Multiply the effect of each concentration (i.e. the difference between the concentration and desired by the calculated volume needed and add together. If the desired concentration of 24% was reached the answer should be zero.
2 times -10 + 5 times +4 = 0