Question

Question #10e83

Answer 1

`"25 g"`

Explanation:

A `"10.0% w/v"` solution contains `"10.0 g"` of solute, which in your case is sodium chloride, for every `"100 mL"` of solution.

In other words, if you take a `"100 mL"` sample of this solution you will end up with `"10.0 g"` of sodium chloride, dissolved in solution, of course.

You are told that the volume of the solution is equal to `"250 mL"`. Since you know that you get `"10.0 g"` of sodium chloride per `"100 mL"` of solution, you can say that the given sample must contain

`250 color(red)(cancel(color(black)("mL solution"))) * overbrace("10.0 g NaCl"/(100color(red)(cancel(color(black)("mL solution")))))^(color(blue)(="10.0% w/v")) = color(green)(bar(ul(|color(white)(a/a)color(black)("25 g NaCl")color(white)(a/a)|)))`

The answer is rounded to two sig figs.

So, in order to make your solution, you should dissolve `"25 g"` of sodium chloride in `"100 mL"` of water, then add enough water to get the final volume to `"250 mL"`.