ENCE 433 Dr. Alba Torrents

FINAL "SHOW ALL WORK" Fall 1996

No partial credit for yes/No; High/Low without explanation

1. Complete the following table to show how the specified property would vary upon the addition of small amount of the chemical specified in column "2"

+ indicates the term increases.

= indicates the term remains the same.

- indicates the term decreases.

(10 %)

2. Determine the pH of assuming all are strong acids and/or bases.

1.00 M NaCl pH =

0.20 M HClO₄ pH =

2.00x10^-4 M HNO₃ pH =

(5 %)

3. Will Pb reduce Zn⁺² ions to Zn when all concentrations are 1 M ?

(E^o (volt) Zn⁺²/Zn = -0.76; E^o (volt) Pb⁺²/Pb = -0.13)

(5 %)

4. Derive an equation that shows how the solubility of various bivalent metal carbonates varies with their solubility product and the partial pressure of CO₂ ([Me⁺²] = f (K_so , P_CO2)). Would [Me⁺²] increase, decrease or remain constant when we increase P_CO2 ?

(10 %)

5. Sodium hypochlorite (NaOCl), household bleach, is a commonly used disinfectant (pK_b = 6.5)

1. Draw the pC-pH diagram for a 1 mM solution
2. Determine the pH of a 1 mM solution
3. Determine the speciation, what are the concentrations of [HOCl] and [OCl^-]
4. Would you need to add acid or base to reach a pH = 7.5
5. What are the concentrations of [HOCl] and [OCl^-] at pH = 7.5

(20 %)

6. Consider the following reaction:

with E^o (MnO₄^-/Mn⁺²) = 1.51 V; E^o (S/ H₂S) = 0.14 V

(a) Write the two half reactions and balance the overall reaction

(b) Which species are oxidized and which are reduced

1. Calculate the cell potential, the free energy change and the equilibrium constant for the reaction.
2. Is the reaction spontaneous?

(e) Compute the cell potential, the free energy change, and the equilibrium constant if the chemical species are present in the following concentration:

H2S = 0.2 atm

H+ = 10-7 M

MnO4- = 0.1 mM

Mn+2 = 10-5 M

S = 1.0 M

H2O = 1.0 M

(25 %)

7. Consider a natural water whose composition is determined by equilibrium with the carbonate solid of metal M at fixed P_CO2 = 10^-3.5 atm where:

MCO₃ (s) = M⁺² + CO₃^-2 Log K = -9.00

1. Indicate all the species present
2. Draw a graph for this system showing all species in solution
3. Calculate the equilibrium pH and alkalinity of the water.
4. Write a balance reaction for the weathering (i.e., dissolution) of MCO₃(s) by CO₂(g) and describe how alkalinity is effected by the weathering reaction.

(25 %)