Determination Of Total Soluble Sulphates In Soils (Volumetric Method) -

STANDARD

OBJECTIVE

APPARATUS

Analytical balance of sensitivity 0.001 gram.
Glass beakers 2 nos of 150 ml capacity.
Glass funnel of 6 cm diameter.
Measuring flasks one of 100 ml and two of 500 ml capacity.
Burette 2 nos of 25 ml with 1/20 ml graduation.
Conical flasks 6 nos of 150 ml capacity.
Pipette 10 ml.
Filter papers.
Heating equipment.
Thermostatically controlled oven of capacity up to 250°C.
Reagents
Barium Chloride solution (N/4) – Dissolve 30.54 gm of barium chloride in one liter of distilled water.
potassium Chromate (N/4) – Dissolve 24.275 gm of potassium chromate in a small amount of distilled water and add a few drops of Silver Nitrate solution to remove any chloride, filter and dilute to 250 ml.
Silver Nitrate Indicator solution (0.5%) – Dissolve 500 mg of silver nitrate in 100 ml of distilled water.
Dilute solution of Ammonium Hydroxide Specific Gravity 0.888).
Mix Ammonium Hydroxide and distilled water in the ratio of 1: 2 (One part of Ammonia and two parts of distilled water).
Concentrated Hydrochloric acid (Specific Gravity 1.11).

PROCEDURE

Take exactly 10 grams of oven dried soil sample well pulverized in a mortar with rubber-covered pestle or in a mechanical device.
Transfer the soil sample in to the beaker and add 50 ml of water
Stir well, allow to decant, filter, wash on a filter paper with small quantity of water and make the filtrate to 100 ml.
Pipette out 10 ml of water extract in to a conical flask.
Make it slightly acidic by adding concentrated Hydrochloric acid and heat to boiling.
While boiling add Barium Chloride solution (N14) from the burette till the precipitation is complete and Barium Chloride solution is in light excess.
Neutralize the solution with ammonium hydroxide and titrate the excess of Barium Chloride against Potassium Chromate solution (NI 4).
If considered necessary the end point can be further conformed by using Silver Nitrate solution as an external indicator.
A brick red colour is obtained when a drop of Silver Nitrate is added to a drop of the chromate solution.

CALCULATIONS

Sulphates as Sodium Sulphate in soil, percent by mass = 0.0177 x 100 (X-Y).
X=Volume of N/ 4 barium chloride added.
Y = Volume of N/4 Potassium Chromate solution used in back titration
X-Y = N/4 barium chloride actually used for perceptibly Sulphate.

REPORT

Report the result obtained as the percentage of total soluble sulphates in the soil.

PRECAUTIONS

Pure chemicals and distilled water shall only be used in the test.
Pure chemicals shall mean chemicals that do not contain impurities that affect the results of analysis.