Chemistry basics

Question

A dimethylsulfoxide (DMSO) - aqueous solution - has a molality of 6.55 m. Calculate the mass percent, mole

fraction, the molarity, and the volume percent of this solution in terms of DMSO. The density of water is

0.9970 g/ml, the density of DMSO is 1.051 g/mL, and the density of the DMSO-aqueous solution is 1.022 g/mol.

The molar mass of DMSO is 78.07 g/mol, and the molar mass of water is 18.02 g/mol

Answer 1

Mass %

6.55 m = 6.55 moles DMSO / kg H2O

6.55 mol DMSO x 78.07 g/mol = 511 g DMSO / 1000 g H2O

Total mass = 511 g + 1000 g = 1511 g

mass % DMSO = 511 g / 1511 g (x100%) = 33.8%

Mole Fraction

moles DMSO = 6.55

moles H2O = 1000 g x 1 mol / 18.02 g = 55.5 moles

Total moles = 6.55 + 55.5 = 62.1 moles

mole fraction DMSO = 6.55 mol / 62.1 mol = 0.105

Molarity

511 g DMSO x 1 ml DMSO / 1.051 g = 486.2 mls DMSO

1 kg H2O = 1000 g x 1 ml / 0.9970 ml = 1003 mls

Total volume = 486.2 mls + 1003 mls = 1489 mls = 1.489 L

molarity of DMSO = moles DMSO / Liter = 6.55 mol / 1.489 L = 4.40 M

Volume %

486.2 mls DMSO / 1489 mls (x100%) = 32.7%