Question #865b5

1 Answer
Jan 18, 2018

Answer:

Here's what I got.

Explanation:

In order to find the solution's percent concentration by mass, #"% m/m"#, you must find the number of grams of solute present for every #"100 g"# of the solution.

You know that a sample of this solution contains #"5 g"# of the solute dissolved in #"50 mL = 50 cm"^3# of the solvent.

I will assume that the pure solvent has a density of #"0.7 g cm"^(-3) = "0.7 g mL"^(-1)#, which means that the #"50-mL"# sample has a mass of

#50 color(red)(cancel(color(black)("mL"))) * "0.7 g"/(1color(red)(cancel(color(black)("mL")))) = "35 g"#

So, the sample contains #"5 g"# of the solute in

#"5 g + 35 g = 40 g"#

of the solution, which means that #"100 g"# of this solution will contain

#100 color(red)(cancel(color(black)("g solution"))) * "5 g solute"/(40color(red)(cancel(color(black)("g solution")))) = "12.5 g solute"#

Therefore, you can say that the solution's percent concentration by mass is equal to

#color(darkgreen)(ul(color(black)("% m/m = 12.5%")))#

I'll leave the answer rounded to three sig figs, but keep in mind that you should report the answer as

#"% m/m = 10%"#

because you have only one significant figure for your values.