Precipitation Titrations Exercise

Week 10 Homework

EDTA & Precipitation Titrations and visual representation of titrations

1. A 40.00 mL solution contains 30.00 mM Co3+ is to be titrated with a 25.00 mM solution of EDTA. Both the cobalt and EDTA solution are buffered to a pH of 10.00. Determine the concentration of cobalt as pCo3+ (pCo3+ = –㏒[Co3+]) for the volumes of titrant listed in the table below.

 Vol. Titrant Added Solution pCo3+ 0.00 mL 26.00 mL 30.50 mL 48.00 mL 50.00 mL 53.25 mL

1. A solution is prepared by mixing the two solutions together. The first solution is 150.0 mL and contains 30.78 mM Ti3+, 29.40 mM Ce3+, and 8.75 mM HCl. The second solution is 200.0 mL and contains 40.23 mM EDTA and 11.48 mM piperidine. Determine the concentration of free (non-complexed) metals when the two solutions are mixed.
2. You wish to titrate all the mercury(I) by precipitation with cyanide because you like to play with dangerous chemicals. You obtain a 50.00 mL solution containing 18.00 mM Hg2(NO3)2 and you titrate it with a 24.00 mM solution of KCN. Determine the concentration of Hg22+ and CN– at each of the titration volumes listed below.

 Vol. Titrant Added [Hg22+] [CN–] 20.00 mL 46.00 mL 68.00 mL 75.00 mL 80.00 mL 90.00 mL

For this problem I want you to sketch the titration curve for the acid-base titration that was done in problem #2 from the Week 8 homework (use the correct values from the posted solution if you didn’t get the answer correct). Once you have made the graph identify the following elements on the trace:

1. The two equivalence points
2. The two buffering regions