SOLUTION: chemist mixes an 8% hydrochloric acid solution with a 5% hydrochloric acid solution. How many milliliters of the 5% solution should the chemist use to make a 750-milliliter solutio

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Question 118111: chemist mixes an 8% hydrochloric acid solution with a 5% hydrochloric acid solution. How many milliliters of the 5% solution should the chemist use to make a 750-milliliter solution that is 7% hydrochloric acid?
Answer by Earlsdon(6294) About Me  (Show Source):
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Let x = the number of milliliters of the 5% hydrochloric acid solution.
Then,(750-x) = the number of milliliters of the 8% hydrochloric acid solution.
The sum of these two amounts is to equal 750 milliliters of 7% hydrochloric acid solution.
The amount of hydrochloric acid in each of these amounts of solution can be written:
x%280.05%29%2B%28750-x%29%280.08%29+=+750%280.07%29 Simplify and solve for x.
%280.05x%29%2B%2860-0.08x%29+=+52.5 Combine like-terms.
-0.03x%2B60+=+52.5 Subtract 60 from both sides.
-0.03x+=+-7.5 Divide both sides by -0.03
x+=+250
The chemist will require 250 ml of the 5% hydrochloric acid solution.