Question #e1868

1 Answer
SCooke
Sep 18, 2017

Mix 468.75 mL 0.5% solution with 281.25 mL 0.1% solution.

Explanation:

Well, practically, if you are in a lab, the simplest thing to do would be to dilute the 50% solution! But, I assume that they really want you to simply mix the two given solutions together to make the math more interesting.

This is similar to a regular molarity or molality mixing problem. Two volumes of two concentrations equal one volume of another concentration, as long as the dimensions are the same. Two equations in two unknowns – no problem.

X + Y = 750 This is the ratio of the two volumes. We can substitute one for the other to use in the next equation. Y = 750 – X

0.5 xx X + 0.1 xx Y = 0.35 xx 750
0.5 xx X + 0.1 xx (750 - X) = 262.5 ; 0.5 xx X – 0.1 xx X + 75 = 262.5

0.4 xx X = 187.5 ; X = 468.75 ; Y = 750 – 468.75 = 281.25

CHECK:
0.5 xx X + 0.1 xx Y = 0.35 xx 750 ; 0.5 xx 468.75 + 0.1 xx 281.25 = 262.5
234.373 + 28.125 = 262.5 ; 262.5 = 262.5 CORRECT!

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