Question

Question #82ae2

Answer 1

`30%`

Explanation:

The trick here is to realize that a solution's mass by mass percent concentration, `"m/m %"`, is defined as the number of grams of solute, which in your case is sugar, present in `"100 g"` of solution.

When you add `"40 g"` of sugar to `"100 g"` of water, the mass of the solution will be

`"40 g + 100 g = 140 g"`

Now, you know that this solution contains `"40 g"` of sugar in `"140 g"` of solution, so use the known composition of the solution to find the number of grams of sugar present in `"100 g"` of this solution.

`100 color(red)(cancel(color(black)("g solution"))) * "40 g sugar"/(140color(red)(cancel(color(black)("g solution")))) = "28.6 g sugar"`

This means that your solution has a mass by mass percent concentration of

`color(darkgreen)(ul(color(black)("% m/m = 30% sugar")))`

The answer must be rounded to one significant figure, the number of sig figs you have for your values.

So, you can say that dissolving `"40 g"` of sugar in `"100 g"` of water will produce a solution that is `30color(red)(%)` sugar, i.e. it contains `"30 g"` of sugar for every `color(red)("100 g")` of solution.