Question #1ee3f

1 Answer
Stefan V.
Oct 22, 2017

#8.91%#

Explanation:

The idea here is that in order to be able to determine the percent concentration by mass of the initial solution, you need to figure out the mass of sodium chloride it contains.

To do that, you use an evaporating dish and evaporate all the water present in the solution, i.e. all the solvent, until you are left with solid sodium chloride, the solute.

So, you know that #"24.57 g"# of this solution contain #"2.19 g"# of sodium chloride.

At this point, your goal is to figure out the mass of sodium chloride present in #"100 g"# of this solution, which is essentially what the solution's percent concentration by mass tells you.

#100 color(red)(cancel(color(black)("g solution"))) * "2.19 g NaCl"/(24.57color(red)(cancel(color(black)("g solution")))) = "8.9133 g NaCl"#

You can thus say that the solution has a percent concentration by mass of

#color(darkgreen)(ul(color(black)("% m/m = 8.91% NaCl")))#

The answer is rounded to three sig figs, the number of sig figs you have for the mass of sodium chloride.

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