# What is the volume of 2.5 moles of nitrogen gas (N2) at standard temperature and pressure (STP)?

Two extra credit Excel calculations:

These calculations must be performed using excel and the excel solver (this is an add-in for excel). You must turn in a print-out of your excel spreadsheet showing the answer. In addition, you must fully explain your calculation on a separate sheet of paper. Ionic strength corrections are not required for these exercises.

Problem 1(20 points):

Consider a mixture of sodium glycolate, sodium lactate and sodium pyruvate at the respective concentrations of 1.00 mM, 8.00 mM and 23.0 mM. Calculate the pH of the solution using the principles of mass and ion balance and the excel solver.

a. Look up the pKa for glycolic acid, lactic acid and pyruvic acid.

b. Write out the ion balance equation for this system.

c. Find the pH and pOH using excel.

d. Calculate the concentration of each acid and its conjugate base in the system.

e. What percentage of the OH- concentration resulted from the auto ionization of water?

Problem 2(20 points):

This problem is related to the carbonate system.

a. Using a charge/mass balance, calculate the pH of 0.001 M NaHCO3 using the excel solver.

b. A 0.001 M solution of NaHCO3 is allowed to come into contact with excess calcite CaCO3(s). Using charge and mass balance considerations (and the excel solver), calculate the pH at equilibrium. What is the equilibrium concentration of Ca2+ in the solution?

Use the following constants for the acidity of carbonic acid and for the solubility of calcite for your calculation.

K1 =10-6.35

K2 =10-10.33 Ksp =10-8.47