Question

The density of a 20.3 M CH 3OH (methanol) solution is 0.858 g/mL.

What is the molality of this solution? H 2O is the solvent.

a)17.4 m

b)20.8 m

c)23.7 m

d)70.0 m

e)97.6 m

Answer 1

Answer:

Molality is 97.6 m (option e)

Explanation:

Density relates mass/volume. It is a data which is involved always to solutions, not solute, neither solvent.

0.858 g/mL = solution mass / 1000mL

0.858 g/mL .1000 mL = 858 grams of solution

Mole of solute = 20.3

Molar weight methanol = 32.04 g/m

Mass of methanol, in solution = molar weight . mol

32.04 g/m . 20.3 = 650.4 g

Mass of solution = Mass of solvent + Mass of solute

858 g = Mass of solvent + 650.4g

Mass of solvent = 858 g - 650.4 g → 207.6 g

So 20.3 moles of solute are contained in 207.6 g of solvent.

Molality is moles of solute/kg of solvent

20.3 m / 0.2076 kg = 97.6 m