Question #7deb5

1 Answer
May 29, 2017

Answer:

The answer is (c) #"236 g"#

Explanation:

Molality is simply a measure of the number of moles of solute present for every #"1 kg"# of solvent.

This means that a #"1-molal"# glucose solution will contain #1# mole of glucose for every #"1 kg"# of solvent.

#"1 molal " implies " 1 mole glucose" color(white)(.)color(blue)("for every")color(white)(.)"1 kg water"#

As you know, you have

#"1 kg" = 10^3# #"g"#

This means that your solution will contain

#"1 molal " implies " 1 mole glucose" color(white)(.)color(blue)("for every")color(white)(.)10^3color(white)(.)"g water"#

Now, the mass of a solution is always equal to

#"mass solution = mass solute + mass solvent"#

This means that the mass of a #"1-molal"# glucose solution that contains #1# mole of glucose and #10^3# #"g"# of water will be equal to

#"mass 1-molal solution" = "mass of 1 mole glucose" + 10^3color(white)(.)"g"#

To find the mass of #1# mole of glucose, use the compound's molar mass

#1 color(red)(cancel(color(black)("mole glucose"))) * "180.156 g"/(1color(red)(cancel(color(black)("mole glucose")))) = "180.156 g"#

This means that the mass of above solution will be

#"mass 1-molal solution" = "180.156 g" + 10^3color(white)(.)"g"#

#"mass 1-molal solution = 1180.156 g"#

Now, you need your target solution to contain

#"0.2 moles glucose" = "1 mole glucose"/color(red)(5)#

Since solutions are homogeneous mixtures, i.e. they have the same composition throughout, you can say that the mass of solution that will contain #0.2# moles of glucose will be

#"mass solution" = "1180.156 g"/color(red)(5) ~~ color(darkgreen)(ul(color(black)("236 g")))#