Question #76765

1 Answer
Stefan V.
Mar 1, 2017

The answer is A).

Explanation:

The thing to remember about a solution's volume by volume percent concentration, "% v/v", is that it tells you the volume of solute present in "100 mL" of solution.

color(blue)(ul(color(black)("% v/v" = "volume of solute"/"100 mL of solution" xx 100%)))

This means that in order for an alcohol solution to have a "40% v/v" percent concentration, it must contain "40 mL" of alcohol, the solute, for every "100 mL" of solution.

This can be calculated by using the above equation

40% = V_"alcohol"/"100 mL" xx 100%

Rearrange to solve for V_"alcohol"

V_"alcohol" = (40 color(red)(cancel(color(black)(%))) * color(blue)(cancel(color(black)(100))) "mL")/(color(blue)(cancel(color(black)(100)))color(red)(cancel(color(black)(%)))) = "40 mL"

Now, don't forget that you need "40 mL" of alcohol for every "100 mL" of solution, which implies that the correct answer is A)

"100 mL solution" = "40 mL alcohol" + "60 mL water"

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