Calcium and magnesium content

ESTIMATION OF CALCIUM AND MAGNESIUM CONTENT IN PLANT

(Versenate Method)

Aim

         To estimate the percentage of calcium and magnesium content in the triple acid extract.

Principle

         Calcium and magnesium get complexed by EDTA in the order Ca first and Mg afterwards. In this experiment Ca is estimated first by using murexide indicator at pH 12 in the presence of sodium hydroxide. The calcium + Magnesium is estimated by using an Eriochrome Black T indicator at pH 10 in the presence of ammonium chloride and ammonium hydroxide buffer solution.

Materials required

         1) 0.02 N EDTA 2) 10 % sodium hydroxide 3) Ammonium Chloride ammonium hydroxide buffer solution. 4) Murexide indicator and 5) Eriochrome black T indicator 6) Porcelain basin, 7) Burette 8) Pipette 9) 25 ml measuring cylinder.

Procedure

Calcium alone

         Pipette out 5 ml of triple acid extract into a procelain basin. Add 10 % Sodium hydroxide drop by drop to neutralise the acidity (red litmus turns blue) and add another 5 ml excess to maintain the pH 12. Add a pinch of murexide indicator and titrate against 0.02 N EDTA till red colour changes from pinkish red to purple or violet.

Calcium & Magnesium

         Pipette out 5 ml of triple acid extract into a porcelain basin. Add ammonium chloride - ammonium hydroxide buffer solution drop by drop to neutralize the acidity and add 5 ml excess to maintain the pH at 10. Add 2-3 drops of Eriochrome black T indicator and titrate against 0.02 N EDTA till the colour changes from wine red to sky blue.

Observation and calculation

Weight of plant sample taken

=

'W' G

Volume of triple acid extract prepared

=

'V' ml

Volume of triple acid extract pipetted out for titration

=

5 ml

Volume of 0.02 N EDTA used for Ca + Mg

=

'A' ml

Volume of 0.02 N EDTA used for Ca alone

=

'B' ml

Volume of 0.02 N EDTA used for Mg alone

=

'A-B' ml

1 ml of 0.02 N EDTA

=

0.0004 g of calcium

Percentage of Calcium in the given sample on moisture free basis

=

1 ml of 0.02 N EDTA

=

0.00024 g of Mg

Percentage of Magnesium in the given sample on moisture free basis

=

Where M = Moisture percentage in the given sample.