Determination of Chlorides in Water

Introduction:

Water is a combination of right proportion of oxygen and hydrogen in it. The water has a standard constituents of various elements whose proportion to be maintained is mandatory such as potassium, sodium, magnesium etc. whereas the excess of these ions may poison the water and obstruct its use for all its applications whether its marine, human, or any other used.

The parameter adopted for its evaluation is based on the following standard usually adopted by titrating the given sample against a solution of silver nitrate. A potentiometric determination approach can also be adopted for the equivalent determination however is least accurate.

The chloride ions have an increased concentration in the wastewater as compared to the raw water. This is because one of the major nutrients and part of food NaCl passes through the digestive system without any change resulting into an increased number of chloride ions in the raw water.

Its increased concentration across the sea might be the result of the salinity because of various water sources. The increased content may result into an increased chances for the deterioration of the factors it passes through such as pipes, walls etc.

These can be adopted to determine the salinity of the sample along with it is an important factor to determine the purity and heavy use of the water sample.

Standard:

The standard adopted is NF ISO 9297

Related theory:

The sample to be tested for if contains the chlorides they are to be titrated against the solution of silver nitrate which precipitates the chloride ions into silver chloride ions being white in color. here the indicator adopted is potassium chromate providing the chromate ions. The reduction in the amount of chloride ions result into an increase in the concentration of the silver ions being a precipitate of reddish brown in color being the end point.

The following reaction takes place:

Ag+ + Cl AgCl(precipitation)

titration of the sample is carried in the acidic sample rusting in the sample in terms of MgCl. the following reagents along with electrodes are adopted. After the precipitation of the sample the indicator reacts with the chromate ions resulting into the change of the colour of the solution.

The brick-red color is provided by the silver chromate formed.

The standards adopted for the working of this experiments are as follows:

Sample volume 0.7mL 5mL 9mL
100 mL 5 mg/L Cl 35 mg/L Cl 64 mg/L Cl
50 mL 10 mg/L Cl 71 mg/L Cl 127 mg/L Cl
15mL 33 mg/L Cl 235 mg/L Cl 425 mg/L Cl

Apparatus:

The following apparatus are included in the test:

  • A burette
  • A pipette of 20 mL
  • A conical flask of 250 mL
  • A measuring cylinders
  • An indicator potassium chromate.
  • A standard solution of silver nitrate for the titration

Procedure:

The procedure adopted is as follows:

  1. A 250 mL of conical flask is filled with 50 mL of the solution of the sample.
  2. An indicator of 1mL is added up in the solution.
  3. The primary color of the mixture prepared is light yellow in color.
  4. This is now titrated against a sample of silver nitrate being 0.0141N and the volume is then determined against the titration process.
  5. Later, the chloride ions are determined by the following calculations adopted.

Observations:

Sample #. Trial #. Sample Volume (mL) Burette Reading Silver nitrate Volume (mL) Chlorides

(mg/L)

Initial Final
1. ——– ——– ——– ——– ——– ——–
——– ——– ——– ——– ——– ——–
——– ——– ——– ——– ——– ——–
2. ——– ——– ——– ——– ——– ——–
——– ——– ——– ——– ——– ——–
——– ——– ——– ——– ——– ——–
3. ——– ——– ——– ——– ——– ——–
——– ——– ——– ——– ——– ——–
——– ——– ——– ——– ——– ——–

Calculations:

The following calculation are adopted:

Chlorine (mg/L) = ((V1– V2)N35.461000)/V = ((V1– V2)500)/V

Where,

V is the total volume

V1 is the volume of silver nitrate.

V2 is the volume of chloride ions.

Description of the sample Concentration of chloride ions.
1. ———-
2. ———-
3. ———-

The result is determined as an average usually.

Comments:

The comments are made on the samples hardness along with its capacity and the hardness by keeping in account the standards adopted whether it is permanent or temporary.

Precautions:

The following precautions are to be adopted:

  1. The calibration of the burette is to be read carefully.
  2. The sample is to be properly diluted against equivalent amounts.
  3. Titration is to be carried out under proper care.
  4. The instruments must be cleaned thoroughly.
  5. A uniform size of the sample is prepared as a standard of 100 mL to maintain the ions concentration in the sample and determine the end point of the sample properly.
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