Question #91ed4

Assuming that you're supposed to calculate the solution's percent concentration by mass, #"% m/m"#, your starting point here will be to use the density of the solution to calculate its mass.

The solution is said to have a density of #"1.12 g mL"^(-1)#, which means that every milliliter of this solution has a mass of #"1.12 g"#.

Your sample will thus have a mass of

#5.00 * 10^2color(red)(cancel(color(black)("mL"))) * "1.12 g"/(1color(red)(cancel(color(black)("mL")))) = "560 g"#

Now, the solution's percent concentration by mass tells you how much solute, which in your case is sodium chloride, #"NaCl"#, you get for every #"100 g"# of solution.

Since you know that #"560 g"# of solution contain #"21.0 g"# of sodium chloride, you can say that #"100 g"# of solution will contain

#100 color(red)(cancel(color(black)("g solution"))) * "21.0 g NaCl"/(560color(red)(cancel(color(black)("g solution")))) = "3.75 g NaCl"#

This means that the solution has a percent concentration by mass equal to

#color(green)(bar(ul(|color(white)(a/a)color(black)("% m/m " = " 3.75% NaCl")color(white)(a/a)|)))#

The answer is rounded to three sig figs.

SIDE NOTE At room temperature, a sodium chloride solution of density equal to #"1.12 g mL"^(-1)# has a percent concentration by mass of about #11%#, so make sure to let me know if this is not the correct interpretation of the problem.

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