CHM 2046C Module 8 Part II Sample Exam Answers

Part U: Molar Mass Determination Problem 5 points

An aqueous solution contains 0.180 g of an unknown, non volatile/non ionic solute in 50.0 g of water. The solution freezes at -0.040 ^oC. What is the molar mass of the solute?

ΔT = k_fp m

-0.040 ^oC = (-1.86 ^oC/m ) m

m = 0.0215 m

Answer:

0.180 g unknown		1000.0 g H2O		167.2 g unknown
-------------	X	-------------	=	------------------
50.0 g H2O		0.0215 mole unknown		1 mole unknown

See McMurray Worked Example 11.14 p 426.

try McMurray Problems 11.25 and 11.26 p427

try McMurray End-of-Chapter exercises 11.100-11.107 p435-436.

See Kotz Example 14.8 p 679

Kotz Work Exercise 14.8 p 679

More sample Molar Mass problems may be found at:

Kotz Chap 14 p694 #39-46

Part V: Osmotic Pressure Problem 5 points

Estimate the osmotic pressure of human blood at 37 ^oC. Assume blood is isotonic with 0.16 M NaCl solution, and assume the van’t Hoff factor i is 1.9 for NaCL. Remember the NaCl is ionic.

R = 0.0821 L∙atm/K∙mol

∏= cRT i

∏= (0.16 mol/L)( 0.0821 L∙atm/K∙mol)(310 K)(1.9)

Answer:

∏= 7.74 atm

Read McMurray Sections 11.8 and 11.9 pages 423-427.

See McMurray worked example 11.12 p424 and 11.13 p425

Try McMurray Problems 11.23 and 11.24 p425

McMurray End-of-Chapter Exercises 11.97-11.99

See Kotz Example 14.10 p 683

Work Kotz Exercise 14.10 p 684

More sample Osmotic Pressure problems may be found at:

Kotz Chapter 14 p695 #51-54