Calibration Procedures For Manganese(II) Standard

-- By EDTA Titration1,2

 

A. Chemicals

A.1 Available

Manganese stock solution (~0.018 M)

1 M ammonium chloride solution

3 M ammonium hydroxide solution

0.1% Pyrocatechol Violet indicator

hydroxylamine hydrochloride

dilute sodium hydroxide (3 M)

 

 

A.2 Prepared by Student

0.01 M EDTA solution, 250 mL (See Appendix I)

 

 

B. Equipment

 

50 mL graduated buret

25 mL and 50 mL pipets

250 volumetric flask

3 250 mL conical flasks

dropper

25 mL graduated cylinder

50 mL beaker

litmus paper

 

 

C. Procedures

 

C.1 In a 50 mL beaker, dilute 5 mL of 3M ammonium hydroxide to give 15 mL of 1M ammonium hydroxide. To this beaker, add 15 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 50 mL of the manganese stock solution to a 250 mL volumetric flask. Also add between 0.063 and 1.00 g of hydroxylamine hydrochloride. Dilute to the mark with deionized water. Pipet 50 mL of the diluted manganese solution into a 250 mL conical flask. Test the pH of the diluted solution with litmus paper. If acidic, add dropwise dilute sodium hydroxide (about 8 - 10 drops) to around neutral pH. Then add 5 mL of the mixture in C.1, and 3 to 5 drops of indicator.

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

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(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 Manganese Solution Certification Notebook.

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

b. Volumetric data for three titrations

c. Average Manganese concentration and standard deviation

 

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

 

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