Question #c92ff
1 Answer
Here's what I got.
Explanation:
Molality is defined as the number of moles of solute present for every
You know that your solution has a molarity of
To make the calculations easier, let's pick a
#3 color(red)(cancel(color(black)("moles NaCl"))) * "58.44 g"/(1color(red)(cancel(color(black)("mole NaCl")))) = "175.32 g"#
Now, use the density of the solution to determine its mass.
#1 color(red)(cancel(color(black)("L solution"))) * (10^3color(red)(cancel(color(black)("mL"))))/(1color(red)(cancel(color(black)("L")))) * overbrace("1.25 g"/(1color(red)(cancel(color(black)("mL solution")))))^(color(blue)("the density of the solution")) = "1250 g"#
To find the mass of water present in the sample, subtract the mass of the solute from the mass of the solution
#m_"water" = "1250 g" - "175.32 g"#
#m_"water" = "1074.68 g"#
This is equivalent to
#1074.68 color(red)(cancel(color(black)("g"))) * "1 kg"/(10^3color(red)(cancel(color(black)("g")))) = "1.07468 kg"#
So, if your solution contains
#1 color(red)(cancel(color(black)("kg water"))) * "3 moles NaCl"/(1.07468 color(red)(cancel(color(black)("kg water")))) = "2.79 moles NaCl"#
Therefore, the molality of the solution will be equal to
#color(darkgreen)(ul(color(black)("molality = 2.8 mol kg"^(-1))))#
I'll leave the answer rounded to two sig figs, but keep in mind that you only have one significant figure for the molarity of the solution.