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Friday, August 9, 2013

The Determination of Magnesium by Direct Titration - Lu Le Laboratory


1.     Submit a clean 500-mL volumetric flask to receive the unknown, dilute to the mark with water, and mix thoroughly.

2.     Transfer 50.00-mL aliquots to 250- mL conical flask.
3.     Add 1 to 2 mL of Ph-10 buffer and 3 to 4 drops of Eriochrome Blake T indicator to each.

Eriochrome Blake T indicator 

4.     Titrate with 0.01M EDTA until the color changes from red to pure blue[1][2].

5.     Express the results as parts per million of Mg2+ in the sample.


[1]    The color change tends to be slow in the vicinity of the end point. Care must be taken to avoid overtitration.
[2]     Other alkaline earths, if present, are titration along with the Mg2+ ; removal of Ca2+ and Ba2+ can be accomplished with (NH4)2CO3. Most polyvalent cations are also titrated. Precipitation as hydroxides or the use of a masking reagent may be needed to eliminate this source of interference.

Experimental Record

Concentration of EDTA
0.010 M
Weight of Standard MgSO4
Consumption of EDTA solution
46.50 mL

46.73 mL
46.62 mL

= 0.4662 mmol
Concentration of Mg2+
0.4662 mmol /50.00 mL

= 9.32 mM
Theory Concentration of Mg2+

= 9.97 M
Percentage of Error

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