Question

an aqueous solution of sodium chloride is marked 10%(w/w) on the bottle. The density of the solution is 1.071g/mL-1. What is the molality and morality also what is the mole fraction of each component is the solution.

Answer 1

GIVEN:

• 10% w/ w means 10 g NaCl in 100 g solution
• Amount of water present in the soln

=100 - 10

= 90 g

• Density of solution =1.071 g/ mL -1

SOLUTION:

(1) MOLARITY

mass of solution = 100 g

Density of solution = 1.071 g/ mL -1

$density = \frac{mass}{vol}$

$vol = \frac{100}{1.07} = 93.45 ml$

$vol = 0.093 \: l$

mass of NaCl =10g

molar mass = 40 g

$moles = \frac{10}{40} = 0.25M$

We know that ,

$molarity \: = \frac{moles \: of \: solute}{vol \: of \: soln}$

$molarity = \frac{0.25}{0.093}$

$molarity =2.68$

(2) MOLALITY

moles of NaCl = 0.25

mass of water =90 g = 0.09 kg

$molality \: = \frac{moles \: of \: solute}{mass \: of \: solvent}$

$molality \: = \frac{0.25}{0.09}$

$molality \: = 2.77m$

(3) MOLE FRACTION

moles of NaCl = 0.25

moles of water = 90/18

moles of water =5

total moles = 5+0.25 = 5.25

mole fraction of NaCl

= moles of NaCl / total moles

= 0.25/5.25

= 0.05

mole fraction of H 20

= moles of H 2 0 / total moles

= 5/5.25

=0.95