Question

In part 2 of lab this week, the unknown organic substance was tolune. Consider that you prepared a solution by mixing 0.151 mL toluene with 4.48 mL of cyclohexane. What is the molality of this solution? Enter your answer in units of molality to three significant figures.

Answer 1

Given,

Volume of toluene(solute) = 0.151 mL

Volume of cyclohexane(solvent) = 4.48 mL

Now,

The formula to calculate molality of a solution is,

Molality = Number of moles of solute / Kg of solvent

We know,

The density of toluene = 0.87 g/ mL

The density of cyclohexane = 0.778 g/ mL

Now, Calculating the number of moles of toluene,

= 0.151 mL x ( 0.87 g /1 mL) x ( 1 mole / 92.14 g)

= 0.001426 moles of toluene

Calculating the mass of cyclohexane in Kg ,

= 4.48 mL x (0.778 g / 1 mL) x (1 Kg/1000g)

= 0.003485 Kg of cyclohexane

Now,

Molality of solution = 0.001426 moles of toluene / 0.003485 Kg of cyclohexane

Molality of solution = 0.409 m

[Note: Please check if the density values provided in the lab manual]