Question #ba9ef

1 Answer
Oct 8, 2017

Answer:

#0.0357#

Explanation:

The idea here is that you need to use the density of the solution to find the mass of a sample of known volume.

As you know, the molarity of a solution tells you the number of moles of solute present for every #"1 L" = 10^3# #"mL"# of this solution.

In your case, a #"0.220-mol L"^(-1)# potassium oxalate solution will contain #0.220# moles of potassium oxalate for every #10^3# #"mL"# of solution.

To make the calculations easier, let's pick a sample of this solution that has a volume of #10^3# #"mL"#. By definition, this sample will contain #0.220# moles of potassium oxalate.

Use the molar mass of potassium oxalate to convert the number of moles to grams

#0.220 color(red)(cancel(color(black)("moles K"_2"C"_2"O"_4))) * "166.22 g"/(1color(red)(cancel(color(black)("mole K"_2"C"_2"O"_4)))) = "36.57 g"#

Now, you know that this solution has a density of #'1.0235 g mL"^(-1)#. This tells you that every #"1 mL"# has a mass of #"1.0235 g"#.

Consequently, this particular sample will have a mass of

#10^3 color(red)(cancel(color(black)("mL solution"))) * "1.0235 g"/(1color(red)(cancel(color(black)("mL solution")))) = "1023.5 g"#

You know no the total mass of the solution and the mass of potassium oxalate it contains, so you can say that the mass fraction of the solute will be

#(36.57 color(red)(cancel(color(black)("g"))))/(1023.5color(red)(cancel(color(black)("g")))) = color(darkgreen)(ul(color(black)(0.0357)))#

The answer is rounded to three sig figs, the number of sig figs you have for the molarity of the solution.