Calibration Procedures For Cobalt(II) Standard

-- By EDTA Titration1,2

cocal.doc 06/22/98

A. Chemicals

 

 

A.1 Available

Cobalt stock solution (~0.17 M)

1 M ammonium chloride solution

3 M ammonium hydroxide solution

0.1% Pyrocatechol Violet indicator

 

 

A.2 Prepared by Student

0.01 M EDTA solution, 100 mL (see Appendix I)

 

 

B. Equipment

 

50 mL graduated buret

5.0 mL and 50 mL pipets

100 and 250 mL volumetric flasks

3 250 mL conical flasks

250 mL beaker

25 mL graduated cylinder

pH paper

 

 

C. Procedures

 

C.1 In a 250 mL beaker, dilute 25 mL of 3M ammonium hydroxide to give 75 mL of 1M ammonium hydroxide. To this beaker, add 75 mL of 1M ammonium chloride and mix thoroughly. This buffer mixture is used below.

C.2 Triple rinse and fill the 50 mL buret with the 0.01M EDTA solution. Drain some solution to fill the tip of the buret. Record initial volume.

C.3 Pipet 5.0 mL of the cobalt stock solution to a 250 mL volumetric flask. Dilute to the mark with deionized water. Pipet 50 mL of the diluted cobalt and add to about 40 mL of deionized water in a 250 mL conical flask. To the flask, add 20 mL of the buffer mixture from C.1. Check the pH with pH paper. If the pH is lower than about pH 9-10; or if the solution becomes turbid, add another 10 mL of buffer. Add 8 drops of 0.1% Pyrocatechol Violet indicator.

C.4 Stir (swirl) the solution mixture in C.3. Titrate it immediately with the 0.01M EDTA solution. The end point should be a color change from blue (blue-green) to reddish-purple. Record the final volume of the EDTA solution. Repeat procedure C.3 to C.4 twice.

_______________________________________________________________

(1) Welcher, The Analytical Uses of Etylenediaminetetracetic Acid, 1958.

(2) Vogel, Textbook of Quantitative Inorganic Analysis, 1961.

 

 

 

D. Report

D.1 Record the following data in your Lab Notebook and in the Cobalt Solution Certification Notebook.

a. Weighing data, calculations, and EDTA solution concentration.

b. Volumetric data for three titrations

c. Average cobalt concentration and standard deviation

D.2 Sign and date the Cobalt Notebook, and label the Cobalt stock solution vessel with the up-dated certified concentration, date certified, and your name.

 

Click here to view and/or print the Table for this section

Click here to view and/or print the Sample Table for this section