Question

PROBLEMS: 3 - 2-1 1. (9 points) Aqueous methanol (CH3OH) can be purchased in a solution with a molality that is 1.52 m and the solution has a density of 0.85 g/mL. What is the molarity of the solution? you already have the moles solute with molality density is mass vowme

Answer 1

Let the mass of solvent be 1 Kg

m(solvent)= 1 Kg

use:

number of mol,

n = Molality * mass of solvent in Kg

= (1.52 mol/Kg)*(1 Kg)

= 1.52 mol

Molar mass of CH3OH,

MM = 1*MM(C) + 4*MM(H) + 1*MM(O)

= 1*12.01 + 4*1.008 + 1*16.0

= 32.042 g/mol

use:

mass of CH3OH,

m = number of mol * molar mass

= 1.52 mol * 32.04 g/mol

= 48.7 g

This is mass of solute

total mass of solution = 1 Kg + 48.7 g

= 1000 g + 48.7 g

= 1.049*10^3 g

This is mass of solution

mass of solution = 1048.70384 g

density, d = 0.85 g/mL

use:

volume = mass/density

= 1.049*10^3 g /0.85 g/mL

= 1.234*10^3 mL

volume , V = 1.234*10^3 mL

= 1.234 L

use:

Molarity,

M = number of mol / volume in L

= 1.52/1.234

= 1.232 M

Answer: 1.23 M