Question

Question #76765

Answer 1

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"`