CHEM 123                           Sample Exam #1 (For Multiple Choice Version see Sample Exam 1B)  

In all problems requiring calculations, your work should be carefully shown!

1.As a solution forms,

a.solute particles separate from each other

b.solvent molecules move apart to make room for solute particles

c.solute molecules and solvent molecules mix

d.a homogeneous mixture forms

e.each of these occurs

2.The substance listed below likely to be most soluble in CCl4 is

a.H2O

b.I2

c.NaCl

d.MgCl2

e.        CH3CH2OH

3.The amount of oxygen gas dissolved in water would be greatest at

a.high temperature with high oxygen pressure above the solution

b.high temperature with low oxygen pressure above the solution

c.low temperature with high oxygen pressure above the solution

d.low temperature with low oxygen pressure above the solution

4.  Connstant boiling HCl(aq) is 20.2 % HCl by mass and has a density of 1.086 g/mL:
  1. Calculate the molality of the solution
  1. Calculate the molarity of the solution
  1. Calculate the mole-fraction of HCl
5.   Kb for benzene is 2.53º C/molal, and it normal boiling point is 80.1ºC.  Calculate the boiling point of a solution containing 11.6 grams of the molecular compound C5H12N2O in 80.0 grams of benzene.

6.  Calculate the osmotic pressure of a physiological saline solution that is 0.154 M NaCl(aq) at 37ºC. (R = 0.821 liter atm/mole K).
 
 

7.(20 pts) The following initial rate data were obtained for the reaction:

ClO2 (aq)         +      OH-(aq) ®     ½ ClO3-(aq)    +    ½ ClO2- (aq)    +    ½ H2O
 
[ClO2], M
[OH-], M
Initial Rate 

Mole/liter sec
0.0575
0.0216
8.21 x 10-3
0.0713
0.0216
1.26 x 10-2
0.0575
0.0333
1.26 x 10-2
0.0713
0.0333
1.95 x 10-2

a. Write the rate expression

b. Calculate k

c. What is the [OH-] when the concentration of ClO2 is 0.100 M and the rate is       3.56 x 10-2 mole/liter sec?.

8. In the first-order decomposition of cyclopropane at 450 K,

C3H6(g) ®        products

it is found that 3.00% of a sample has decomposed in 100.0 seconds. Calculate

a. the rate constant

b. the half-life

9. 5. (15 pts) Nitrogen monoxide converts ozone into molecular oxygen :

O3        +      NO ®     O2     +     NO2

The experimental rate law is: rate = k[O3][NO]. Which of the following mechanisms are consistent with the experimental rate law?

Mechanism I:          O3     +    NO ®          O       +      NO3       (slow)

                               O       +    O3®      2O2       (fast)

                               NO3   +   NO ®       2NO2     (fast)

Mechanism II:        O3®       O       +       O2       (fast, reversible)

                              NO      +   O ®         NO2        (slow)

Mechanism III:       O3       +   NO ®        O2      +      NO2

(Note, you must provide some supportive information in order to be given partial credit)