Question

Question #e1868

Answer 1

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!