Home /
Expert Answers /
Chemistry /
post-laboratory-assignment-complete-the-discussion-questions-and-post-lab-problems-in-your-lab-noteb-pa272

Post-laboratory Assignment Complete the discussion questions and post-lab problems in your lab notebook. Discussion questions Identify three factors that influence the magnitude of the freezing point depression. From a molecular-level perspective (with respect to atoms/ions/molecules), explain why the freezing point of the solution is lower than the freezing point of pure solvent. In Part 2, suppose 10 mL of cyclohexane was added to the test tube, instead of 12 mL . Would the change in volume have an impact on the measured freezing point? Explain your reasoning. Cyclohexane has a vapor pressure of 98 torr at

`25\deg C`

. If the mass of cyclohexane decreased due to vaporization (and assuming no impact on

`\Delta T_(f)`

), explain how this impacts the

`K_(f)`

value determined in Part 3. Postlab problems Consider a

`0.0500mHClO_(2)`

(aq) solution.

`HClO_(2)`

is a weak acid; only

`36%`

of the molecules dissociate when dissolved in water. a. Calculate the van't Hoff factor,

`i`

, for this solution if

`HClO_(2)`

is

`36%`

dissociated through the following reaction:

`HClO_(2)(aq)⇄H^(+)(aq)+ClO_(2)^(-)(aq)`

Hint: Assume 100 molecules of

`HClO_(2)`

. Calculate how many total particles are present after

`36%`

of the molecules have dissociated and compare it to the original number of particles. For comparison: The acid HCl , a strong electrolyte acid, is

`100%`

dissociated when dissolved in water and

`i=2:HCl(aq)->H^(+)(aq)+Cl^(-)(aq)`

The acid HCN , a very weak electrolyte acid, is essentially

`0%`

dissociated and

`i=1:HCN(aq)-x->H^(+)(aq)+CN^(-)(aq)`

b. Calculate the freezing point of the

`0.0500mHClO_(2)(aq)`

solution. 2. Calculate the osmotic pressure of

`0.0500mBClBat_(2)`

at

`25\deg C`

. The density of 0.0500 m

`BaCl_(2)`

at

`25\deg C`

is

`1.05(g)/(m)l`

; the molar mass of

`BaCl_(2)`

is

`208.2(g)/(m)ol`

. 3. A CHE 152 student determines the freezing point of the solvent ethylene dibromide to be

`9.79\deg C`

. The student dissolves 1.023 g benzoic acid in 23.482 g ethylene dibromide and measures a freezing point of

`7.69\deg C`

for the solution. The molal freezing point depression constant for ethylene dibromide is

`11.8\deg (C)/(m)`

. a. Assuming the van't Hoff factor is exactly one, calculate an experimental value for the molar mass of benzoic acid based upon the measurements above. b. Calculate the theoretical molar mass of benzoic acid,

`C_(7)H_(6)O_(2)`

. Use the theoretical molar mass to calculate the experimental van't Hoff factor based upon the measurements above. 6