Final Exam, Spring 2005

1. Complete and balance the following chemical equations.

a. aqueous perchloric acid plus aqueous potassium hydroxide

b. aqueous phosphoric acid plus aqueous magnesium hydroxide

c. HCN(aq) + NH₃(aq)

d. Co(CH₃CO₂)₂(aq) + H₂S(aq)

e. Fe³⁺(aq) + EDTA^4–(aq)

f. aqueous bicarbonate ion plus aqueous cyanide ion

g. Cu(s) + HNO₃(aq) → Cu²⁺(aq) + NO₂(g)

h. Al(s) + MnO₄^–(aq) → Al(OH)₃(s) + MnO₂(s)

g. H₂C₂O₄(aq) + CrO₄^2–(aq) → Cr³⁺(aq) + CO₂(g)

2. For each of the following solutions or mixtures, estimate the molar concentrations of all dissolved ions and molecular species (except water) and then estimate the pH of the solution.

a. 0.1 M hydrobromic acid

b. 0.1 M sodium hydroxide

c. 0.1 M Na₂CO₃

d. 0.1 M Fe(NO₃)₂

e. 0.1 mol Al(OH)₃ placed in 1 L of water

3. A reaction, A(aq) + B(aq) → products, has a rate law that is first order in each reactant at 25 °C.

a. Write the rate law for the reaction.

b. If the concentration of A is doubled, how does the reaction rate change and how does the rate constant change?

c. If the concentration of A is doubled and simultaneously the concentration of B is halved, how does the reaction rate change and how does the rate constant change?

d. If the temperature is doubled, how does the reaction rate change and how does the rate constant change?

4. Consider the reaction between hydrogen phosphate ion and carbonate ion.

a. Write the balanced reaction.

b. Find ΔH° for the reaction.

c. Find ΔS° for the reaction.

d. Find ΔG° for the reaction at 25 °C.

e. Calculate the equilibrium constant for the reaction using two different methods. Compare the two values.

5. Consider the reaction:

[Al(OH)₄]^–(aq) + Zn(s) → [Zn(OH)₄]^2–(aq) + Al(s)

a. Write the balanced oxidation half-reaction in base.

b. Write the balanced reduction half-reaction in base.

c. Write the balanced net reaction in base.

d. Write the cell notation for the reaction at standard conditions.

6. Briefly answer the following questions:

a. Zn(OH)₂ is more soluble in a solution that is buffered with pH = 10 than in a solution that is not buffered with pH = 10. Explain.

b. A solution of hydrochloric acid with pH = 4 and a solution of acetic acid with pH = 4 are prepared. If equal volumes of each solution are titrated with 0.1 M sodium hydroxide, which solution requires more base and why?

c. H⁺ and H₃O⁺ are used interchangeably to represent the cationic autoionization product of water and any associated chemical reactivity. Despite this, the thermodynamic parameters for the two ions are different. Suggest an explanation.

d. What does entropy measure?

Answers