Precipitation Titration of Cobalt Chloride
LEASE NOTE: Titration requires several steps in order to obtain exact results. The procedures described in this lab assume that you have already done the TITRATION TUTORIAL and are familiar with the technique.
1. Take a 150 mL Erlenmeyer flask from the Glassware shelf and place it on the workbench.
2. Add 10 mL of cobalt chloride solution (CoCl2) to the flask. Dilute the solution by adding 10 mL of water. This makes it easier to visualize the endpoint, but remember that the concentration of the CoCl2 solution relates the moles of CoCl2 to the original 10 mL.
3. Add 1 drop of thymolphthalein to the flask.
4. Take a burette from the Glassware shelf and place it on the workbench.
5. Fill the burette with 50 mL of 0.1M sodium hydroxide (NaOH).
6. Drag the flask and drop it on the lower half of the burette to connect them.
7. Open the Data window and click on the flask. Click the Pushpin icon in the blue bar of the Data window to lock its display to the flask's contents.
8. Open the Properties window, click on the burette and click the Pushpin icon in the blue bar of the Properties window to lock it to the burette.
9. Titrate the cobalt chloride solution with sodium hydroxide. As the CoCl2 in the flask is used up, the pink color will disappear. The endpoint of the titration is reached when the solution becomes basic and the thymolphthalein turns blue. Record the start and end volumes of the sodium hydroxide solution in the burette.
10. Repeat the titration two more times.
Assignment
1. Record your results for each of the 3 trials:
(a) Volume of CoCl2 (mL):
(b) Volume of NaOH added (mL):
(c) Concentration of NaOH added:
2. Calculate the concentration of the CoCl2 solution (moles/L) using the formula developed in the Background.
3. What is the average concentration of the CoCl2 solution? To how many significant digits can this concentration be reported? (Consider the accuracy of the burette and the volume in one drop.)
My responses thus far.
1.)
(a) 10 mL
(b) 19.00 mL
(c)??