7
titration and signals that all the Ca2+ has reacted with EDTA. Weigh the bottle to
determine the exact amount of EDTA added.
e. Dispose of the solution in the titration bottle and wash it with distilled water. Repeat
the procedure at least three times or until you are confident of your titration skills. In
order to evaluate these skills, you will need to do some arithmetic calculations: The
simplest way to check your skills is to calculate the number of grams of EDTA
solution/grams of Ca2+ solution for each trial. They should be nearly the same for all
three titration trials.
Determining the concentration of M2+ (as a measure of solubilities) in saturated solutions
of salts. The titration procedure is nearly identical to that used for the calcium standard.
For these solutions, it is necessary to filter them to ensure that no solid is transferred.
After filling a syringe (use a separate labeled syringe for each solution) with solution,
remove the needle and attach a 0.45 m m disposable filter to the syringe. Push the solution
through this filter into the titration bottle. The same filter may be used for all the titration
trials for a particular solution. Record the weights at all stages in the titration.
If you find that the amount of EDTA used is too small to measure accurately for any of
the solutions, you may wish to do additional titration trails with a more dilute
(1.25 x 10-3 M) EDTA solution.
Analysis of titration data to evaluate relative solubilities.
1. Organize the titration data in a table similar to the one below (with similar entries for
the solutions of CaSO4 and BaSO4):
Sample and Trials
Trial 1
Trial 2
Trial 3
grams
grams
grams
A. Saturated solution of CaCO3
Weight of Sample
Weight of EDTA used
Weight of EDTA/Weight of sample
Moles of M2+ in solution
2. From the titration results [average of the three values for Weight of EDTA/Weight of
sample), determine the relative solubilities of the three compounds. Which one is the
most soluble? The least soluble?
3. From number of moles of M2+ (average of three trials), express the solubilities in
moles/liter, grams/liter, and grams/100 ml. Compare your results with values you find in
the CRC Handbook (Note that the CRC Handbook includes numerical values for
solubilities in g/100 mL only in editions before 1998.).
4. Conclusions. Write a short paragraph summarizing your findings regarding the
solubility of these three salts and the implications of your findings for the protection
of outdoor monuments carved in limestone (CaCO3) from the detrimental effects of
acid rain, primarily dilute solutions of sulfuric acid.
D. Effects of acid rain on Frescoes (Optional, extra credit). Devise and carry out an
experiment to test the effects of dilute solutions (1 x 10-3 or 1 x 10-4 M) of HCl and H2SO4
(acid rain) on the stability of fresco paintings. Dilute acid solutions will be available.
