Question

The mole fraction of copper(II) nitrate in an aqueous copper(II) nitrate solution is 0.127. What is the molality of the copper(II) nitrate solution? Molality Submit Answer Try Another Version 8 item attempts remaining

Answer 1

Let total mol of solution be 1 mol.

Then mol of Cu(NO3)2 is 0.127 mol

Mol of H2O = 1 - 0.127 = 0.873 mol

Molar mass of H2O,

MM = 2*MM(H) + 1*MM(O)

= 2*1.008 + 1*16.0

= 18.016 g/mol

use:

mass of H2O,

m = number of mol * molar mass

= 0.873 mol * 18.02 g/mol

= 15.73 g

= 0.01573 Kg

Now use:

Molality = mol of Cu(NO3)2 / mass of solvent in Kg

= 0.127 mol / 0.01573 Kg

= 8.07 molal

Answer: 8.07 m