To determine the Chloride Concentration in given sample of water

To determine the Chloride Concentration in given sample of water

DISCUSSION:

Chloride is the common anion found in water and sewage. The concentration of chloride in natural water varies from few milligram to several thousand milligram per liter High concentration of chloride may be due to the contamination by see water, brines , sewages or industrial effluent such as those from paper works, galvanizing plants, water softening plants and petroleum refineries.

PRINCIPLE:

Silver nitrate reacts chloride ions to form sliver chloride. The completion of reaction is indicated by the red colour produced by the reaction of silver nitrate with potassium chromate solution which is added as an indicator

AgNO3 + Cl → AgCl + NO3-

2AgNO3+ KCrO4 → Ag2CrO4 +2KNO3

REAGENTS:

1- Standard Sliver nitrate Titrant 0282N: Dissolved 4.791g silver nitrate, AgNO3 in distilled water ad make up to 1000ml. standardized it against 0.0282N Sodium Chloride solution.

2- Standard sodium Chloride Litrant 0.028N: Dissolve 1.648g sodium chloride, NaCl and make up to 1000ml with Distilled water.

3- Potassium Chromate Indicator solution: Dissolve 25g of potassium chromate, K20:04 in 100ml distilled water. Add silver nitrate solution drop wise until a slide red precipitate is formed. Allow to stand for 12hours. Filter and dilute the filtrate to 500ml.

PROCEDURE:

For Clear Sample:

Place 100ml of the sample or an aliquot containing not more than 10mg chloride in a porcelain basin of about 300ml. capacity (If the pll of the sample is in the range of 7-9.5 it can directly titrated. If the pH is not in the range, adjust the pH by using Sulphuric acid or sodium hydroxide.

Add 1ml Potassium chromate indicator solution. Titrate against silver nitrate solution with constant stirring until a slightest perceptible reddish coloration persists.

Conduct a blank by placing 100ml distilled water instead of sample. A blank of 0.2 to 0.3 ml is usual for the method.

For Closed and Turbid Sample:

If the sample is highly turbid or colored, add 3ml aluminum hydroxide to measure volume of the sample in a beaker. Stir well and allow to settle. Filter and wash the precipitate with distilled water. Combine the filtrate and washings (brings the pll in the 7 – 9.5 range if necessary’) and titrate as above

Stirrer (fig)

CALCULATIOS:

If the normality of agno3 solution is exactly 0.0282 n then mg/l of chloride

OBSERVATION: