Question #82ae2

1 Answer
Oct 6, 2017

Answer:

#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.