Chloride content in Thermal insulation Material

Principle: 

The chloride present in the sample is extracted by titration method with silver nitrate. 

Apparatus/Equipment:

• Burette – 50 ml
• Conical flask – 250
• Balance
• Whatman Filter Paper No. 42
• Beaker – 500 ml
• Water bath

Reagent/Chemical:

• Silver nitrate (0.0141 N) – Dissolving 2.396 g of silver nitrate in distilled water and dilute to 1 liter.
• Potassium Chromate – Dissolving 50 g of potassium chromate in distilled water. Add silver nitrate solution till a definite red precipitate is formed. Allow to stand overnight and filter. Dilute the filtrate to 1 liter with distilled water.
• Sodium Chloride (0.0141 N) – Dissolving 0.8241 g of NaCl in distilled water and dilute to 1 liter.
• 0.1 N  Sulphuric Acid
• 0.1 N Sodium Hydroxide
• Distilled water.

Procedure: 

• Take 30 g of mineral fibre in a 500 ml beaker and 300 ml chloride-free distilled water. 
• Cover the beaker and place it in a steam bath overnight and add fresh water for evaporation losses. 
• Filter through Whatman No. 42 or equivalent filter paper. 
• Take 100 ml of the above extract and adjust the pH in the range 7 to 10 by adding 0.1 N sulphuric acid or 0.1 N sodium hydroxide solution. 
• Add 1 ml of potassium chromate indicator solution. 
• Titrate with standard silver nitrate solution to a pink-yellow end point. Run a blank also. 

NOTE — Chloride contamination should be avoided at all stages during test.

Calculations:

Chlorides (as Cl), % = (V1-V2) × 0.05 / M

where 

 V1 = volume, in ml, of standard silver nitrate solution used in the titration with test sample;
 V2 = Volume in ml of standard silver nitrate solution used in the blank;