Acid-Soluble Chloride Analysis Test in Soil.
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Acid-Soluble Chloride Analysis Test in Soil.

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Acid-Soluble Chloride Analysis Test in Soil.


Principle.

For the determination of acid-soluble chlorides, which includes chlorides not extracted by water, chlorides are extracted from dry soil sample with dilute nitric acid. Results are expressed as the chloride content.

The acid-extract method is applicable to the determination of the chloride content of soils from desert areas or where the origin of the chlorides is uncertain.

Reagents and Apparatus.

  • Burette, 50 mL 
  • Weighing balance 
  • Stoppered conical flask, 500 mL 
  • Beaker, 500 mL 
  • Measuring cylinder 
  • Hot plate 
  • Filter paper, coarse grade  
  • Filter funnel 
  • Nitric Acid 
  • N Silver Nitrate Solution 
  • N Potassium Thiocyanate Solution  
  • 3-5-5-Trimethylhexan-1-ol 
  • Ferric alum indicator  

Procedure.

Standardization of potassium thiocyanate solution.

Transfer 25 mL of the silver nitrate solution into a 250 mL conical flask, using a pipette, and  add 5 mL of the nitric acid solution and 1 mL of ferric alum indicator solution. Add  thiocyanate solution from a burette until the first permanent color change occurs, that is  from colorless to pink. Record the volume of thiocyanate solution added V1 (in mL). Calculate the concentration C (in mol/L) of the solution from the following equation: C =2.5/  V1.

Preparation of test specimen.

Obtain an initial sample. Dry this sample in an oven at 105 °C to 110 °C, and cool to room  temperature in the desiccator. Sieve the sample on a 150 µm test sieve. Crush all retained  particles to pass the 150 mm sieve and mix thoroughly with the material already passing the  sieve. Divide the material by successive riffling to produce test specimens each of about 10  g. Dry the test specimens in the oven at 105 °C to 110 °C and allow to cool in the  desiccator.   

Preparation of acid-soluble chloride extract.

Weigh 5+0.005 g of soil sample in a 500 mL beaker. Add 50 mL distilled water, followed by  15 ml nitric acid. Heat the sample to near boiling and kept warm for 10-15 minutes. Filter  through coarse grade filter paper into a conical flask. Wash the filter paper with hot water  and collect the filtrate and allowed to cool. Add silver nitrate solution until all the chloride has  been precipitated, then add little excess of silver nitrate. Add 2 mL 3-5-5-trimethylhexan-1-ol  and shake the flask vigorously to coagulate the precipitate. Add 5 mL ferric alum indicator  and titrate with standardized Potassium Thiocyanate solution until the first permanent color  change occurs, that is from colorless to red. Record the volume V3 (in mL) of thiocyanate  solution added.

Calculation.

Chloride Content= 0.07092(V2-10CV3) 

Where: V2= volume of silver nitrate solution added 

               V3= volume of standardized potassium thiocyanate solution added 

               C= concentration of standardized potassium thiocyanate solution  

Reference.

BS 1377 Part 3:1990 Amd 9028 :1996.

   











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