exam #4 93

1. At 1.013 bar pressure propane boils at 42.1 C and n-butane boils at -0.5 C. The following vapor pressure data are also available.

t/C	-31.2	-16.3
P/kPa Propane	160.0	298.6
P/kPa n-Butane	26.7	53.3

a) Assuming these substances for an ideal solution, a) calculate the mole fractions of propane at which the solution will boil at 1.013 bar at -31.2 C and -16.3 C.

b) What is the mole fractions of propane in equilibrium with the solutions at these two temperatures.

2. The following cooling curves have been found for the system antimony-cadmium:

Cd wt%	0	20	37.5	47.5	50	58	70	93	100
1st break oC		550	461		419		400
Plateau oC	630	410	410	410	410	439	295	295	321

Construct the phase diagram, assuming that no breaks other than those listed occur. Label the diagram completely and give the formula of any compound formed.

3. If the heat of fusion of t-butanol is 3.6 kJ/mol at its freezing point of 24.5 ^oC; what is its freezing point depression constant?

4. A solution is 0.04 m CuSO4

a) Calculate the ionic strength

b) calculate mean activity coefficient of ions by using the extended Debye Huckel theory.

c) If the DfGo = -649.04 kJ for ionized CuSO4, what is the DfG of the CuSO4 at 0.04 m?

5. For the galvanic cell

H2(1bar)|HCl(ai)|Cl2(1 bar)

the standard cell potential at 298 K is 1.03604 and its derivative with repect to temperature is -1.247x10-3 volts/K. What are the values of DGo, DHo, and DSo of the reaction?

6. What would be the apparent pKa for phenol in a solution that had a 0.1 M ionic strength.

7. Fumarase catalyzes the reaction:

Fumarate + water = L-malate

At 25 C and pH=7, the value of K' is determined to be 4.4. What is the value of K' at pH = 5 given that the pKa's of fumaric acid and L-malic acid are 4.18 and 4.75 respectively.

6. Calculate the DGo of reaction:

H2O(l) = H+(aq) + OH-(aq)

From

a) the free energies of formation in the appendix,

b) from the cell potentials on p 238 and

c) from Kw = 1.008x10-14.

7. a) Derive the equation:

PV = n₂ RT

for the osmotic pressure of a solution of n₂ moles of solute in V of solution.

b) What would you estimate the osmotic pressure of a solu

tion formed from dissolving 1.2 grams of sucrose (C₁₂H₂₂O₁₁) to make 100.0 mL of aqueous solution.