Question

Question #07095

Answer 1

`"16.9 g NH"_3`

Explanation:

A solution's percent concentration by mass, or `"% m/m"`, essentially tells you how many grams of solute you get for every `"100 g"` of solution.

In your case, an ammonia solution that is `"12.5% m/m"` ammonia, `"NH"_3`, will contain `"12.5 g"` of ammonia, which is the solute, for every `"100 g"` of solution.

This means that you can essentially use the solution's percent concentration as a conversion factor to help you go from grams of solute to grams of solution or vice versa.

In your case, `"135 g"` of this ammonia solution will contain

`135 color(red)(cancel(color(black)("g solution"))) * overbrace("12.5 g NH"_3/(100color(red)(cancel(color(black)("g solution")))))^(color(purple)("= 12.5% m/m")) = color(green)(|bar(ul(color(white)(a/a)"16.9 g NH"_3color(white)(a/a)|)))`

The answer is rounded to three sig figs.

Now, you can use the exact same approach to find the volume of fruit juice present in `"250 mL"` of a `"15% v/v"` solution.

This time, you're dealing with percent concentration by volume, or `"% v/v"`, which essentially tells you the volume of solute that you get for every `"100 mL"` of solution.

Use this concentration as a conversion factor to get the answer. You should end up with `"37.5 mL"`.