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Spring 2003

1. Complete and balance the following reactions.

a. Ca(OH)2(s) + HClO4(aq)

b. NH3(aq) + HI(aq)

c. NH3(aq) + HN3(aq)

d. NH3(aq) + CdCO3(s)

e. methylamine plus water

f. Pb(C2H3O2)2(aq) + HCl(aq)

g. Zn(NO3)2(aq) + Cs2S(aq)

h. solid strontium chloride plus aqueous sodium sulfate

i. HI(aq) + ClO(aq) I3(aq) + Cl(aq)

j. Zn(s) + MnO4(aq) MnO2(s) + Zn(OH)2(s)

2. A 1.0 L vessel was prepared with a 1.0 M solution of hydrogen carbonate ion and a 1.0 M solution of hydrogen phosphate ion. The amount of hydrogen carbonate ion was monitored and after 10.0 s, 0.97 mol of hydrogen carbonate ion was found.

a. Write the net reaction.

b. Find the average rate of reaction in terms of loss of hydrogen phosphate ion over the initial ten second time interval.

c. The rate of reaction doubles when the concentration of hydrogen carbonate ion doubles. What is the order of reaction with respect to hydrogen carbonate ion?

d. Estimate the equilibrium constant for the reaction.

3. Gof for CO2(g) listed in the thermodynamic table is –394.4 kJ/mol. A student tries to calculate this value using Hof and So from the table and finds Gof = –393.5 – (298)(0.2136) = –457.2 kJ/mol. The two values obviously do not match and the difference cannot be explained by experimental error. Show the correct way to find Gof for CO2(g). Hint: write a chemical reaction.

4. Estimate the pH of a 0.10 M solution of Fe(NO3)2 at 25 °C. Write the appropriate chemical reactions, set up the problem and work through to the algebra stage. Then make a chemically reasonable estimate of the pH.

5. Consider the reaction between solid calcium hydroxide and aqueous phosphoric acid.

a. Write the balanced chemical reaction.

b. Find Ho at 25 °C for the reaction in units of kJ/mol.

c. Find So at 25 °C for the reaction in units of J/mol•K.

6. Consider the solubility of barium hydroxide at 25 °C.

a. Estimate the molar solubility of barium hydroxide in pure water.

b. To the nearest whole number, what is the pH of a saturated solution of barium hydroxide?

7. Consider the cell Au(s) | [AuCl4](aq) | Cl(aq) || VO2+(aq) | VO2+(aq), pH = 1 | Pt(s).

a. Write the oxidation half-reaction.

b. Write the reduction half-reaction.

c. Write the net reaction for the cell.

d. Find Eo for the cell.

e. Is the reaction spontaneous or nonspontaneous under standard conditions? Why?

f. At high enough pH, the cell is nonspontaneous. Under these conditions, a sufficient voltage is applied so that 100 mA of current is run through the cell for 100 s. Estimate the number of moles of VO2+ that is consumed or produced.