Secondary Elements Estimation Of Soil

1. SECONDARY ELEMENTS
ESTIMATION OF SOIL
AYUSH
20150040

2. PRINCIPLE OF CALCIUM AND MAGNESIUM
Calcium and magnesium get complexed by EDTA in the
order of Ca first followed by Mg. Ca is estimated first
by using murexide indicator in the presence of
sodium hydroxide at pH 12. Then Ca + Mg is estimated
Using Eriochrome Black T in the presence of ammonium
chloride and ammonium hydroxide buffer solution
at pH 10.

3. APPARATUSREQUIRED
Pipette 10 mL
Burette 50 mL
Porcelain basin
Measuring cylinder 10 mL

4. REAGENTS
0.02 N EDTA
10% sodium hydroxide
Ammonium chloride – Ammonium hydroxide
buffer solution
Murexide indicator (Ammonium purpurate)
Eriochrome Black –T indicator

5. PROCEDURE
Calciumalone
 Pipette out 10 mL of sesquioxides filtrate into a porcelain
basin.
 Add 10% sodium hydroxide solution drop by drop to neutralize
the acidity (red litmus turns blue) and another 5 mL excess to
maintain the pH at 12.
 Add a pinch (50 mg) of murexide indicator and titrate with
0.02N
EDTA till the colour changes from pinkish red to purple or
violet

6. CALCIUM+ MAGNESIUM
 Pipette out 10 mL of sesquioxides filtrate into a porcelain
basin.
 Add ammonium chloride – ammonium hydroxide buffer
solution drop by drop to neutralize the acidity(use red
litmus paper) and 5 mL excess to maintain the pH at 10.
 Add 2-3 drops of Eriochrome Black -T indicator solution
and titrate with 0.02 N EDTA till the colour changes from
purple red to sky blue.

7. PRINCIPLE OF SULPHUR
The sulphate in the soil solution is extracted by calcium
Chloride is converted into barium sulphate by adding solid
barium chloride in the presence of gum acacia to make
the colloid very stable at pH 4.8 which is maintained
by adding sodium acetate-acetic acid buffer. This
eliminates the interference of phosphate, silicate etc.

8. APPARATUS REQUIRED
100 mL shaking bottle
Reciprocating shaker
Measuring cylinders 25 mL,10 mL
25 mL volumetric flask
Pipette 5 mL, 1 mL
Spectrophotometer/ photoelectric
colorimeter

9. REAGENTSREQUIRED
1. Potassium sulphate solution:
Weigh exactly 0.2718 g of AR Potassium sulphate.
Dissolve in a few mL of ordinary distilled water
in one litre flask and make the volume to one litre.
This solution contains 0.05 mg of sulphur per mL.

10. 2. SODIUM ACETATE-ACETIC ACIDBUFFER:
Weigh 100g of pure sodium acetate and dissolve it in suitable
amount of water. To this add 31 mL of glacial acetic acid (A.R)
and make the volume to one litre. This solution contains
0.05 mg of sulphur per mL.
3. Gumacacia
Dissolve 2.5 g of gum acacia in a litre of distilled water
keep overnight and filter.

11. PROCEDURE
 Weigh 5.0 g of soil into a 100 mL shaking bottle
 Add 25 mL of 0.15 % CaCl2 and shake for 30 minutes in a
reciprocating shaker
 Pipette out 5 mL of extract into a 25 mL volumetric flask
 Add 10 mL buffer, 1 mL gum acacia and 1 g BaCl2.
 Make up the volume with distilled water and shake well
 Read the absorbance of this solution in a spectrophotometer at
420 nm after adjusting the meter to zero per unit absorbance
with the blank
 Calculate the sulphate content using the standard curve.

12. PREPARATION OF STANDARD CURVE
Dissolve 0.2718 g of AR grade K2SO4 in distilled water in a 1000
mL volumetric flask and make up the volume to the mark.
This solution contains 0.05 mg S per mL. Using the graduated
pipette, transfer 1,2,3,4,5,6 and 8 mL of K2SO4 solution in to 25
mL volumetric flasks separately. To each flask, add 10 mL buffer,
1 mL gum acacia and 1 g BaCl2. Shake well and make upto the
volume with distilled water. Read the absorbance of each solution
using a spectrophotometer. Plot the spectrophotometer readings
in a graph against the corresponding concentrations of S. Use
this as a standard for the corresponding concentrations for
finding out the concentration of S in soil sample.