Estimation of chloride

 ESTIMATION OF CHLORIDES IN THE SAMPLE WATER

AIM:- To determine the concentration of chlorides in the given sample water.

APPARATUS:- Glassware.

THEORY:- Chloride is a major inorganic constituent of natural waters. Chlorides ions may be in combination with cations like calcium, magnesium, iron and sodium. Chlorides of these minerals are present because of their high solubility in water. The other sources of chlorides in the water are intrusion of sea water into fresh water bodies, pollution of industries waste and domestic wastes.

            The chloride content of water is measured by titrating the water sample with standard silver nitrate solution (AgNo₃) using potassium chromate k₂cr₂o₇ as indicator. The silver first reacts with all chlorides thereby forming silver chlorides as indicated by the following equation.

            Nacl + Agno₃ (titrant) → Agcl + NaNo₃ 

            The silver chloride so formed then reacts with potassium chromate (indicator) to form silver chromate producing reddish precipitate which indicates the end point. This reaction is indicated by the following reaction.

            2Agcl + k₂cro₄ → Ag₂cro₄ (reddish precipitate) + 2Kcl.

            The amount of silver nitrate required to produce reddish precipitate determines the amount o chlorides present in the water sample.

RELEVANCE:- The permissible limit of chloride in domestic water supplies is upto 250ppm. Although chlorides in excess of 250ppm are not harmful, but they cause unpleasant taste to water, thus rendering the water unacceptable for drinking purpose. The presence of large quantity of chlorides in water indicated its pollution due to sewage. The chloride concentrations of raw waters being used for public water supplies should therefore tested regularly, as to detect any sudden increase in their chloride content and the possibility of the organic pollution of the water source.

REAGENTS:-

1. Potassium chromate indicator:- Dissolve 10.0grams k₂cro₄ in a little distilled water. Add silver nitrate solution until a red precipitate is formed. Let stand 12 hours, filter and dilute it to 200ml with distilled water.
2. Standard silver nitrate solution (0.0141N):- Dissolve 2.395 grams AgNo₃ in distilled water and dilute it to 1000ml. standardize against 0.0141N sodium chloride solution as per the procedure described below. Store it in a brown glass bottle.
3. Standard sodium chloride (0.0141N):- Dissolve 824.1mg Nacl in chloride free water and dilute it to 1000ml.

PROCEDURE:-

1. Standardization of AgNo₃ (Titrant):- Take 20ml standard sodium chloride solution and dilute it to 100ml. add 1ml k₂cro₄ indicator. Titrate with AgNo₃ solution to pinkish yellow end point. Note down the volume of AgNo₃ consumed and determine the normality of AgNo₃ using the relation

N₁V₁ = N₂V₂

Where

N₁ = Normality of AgNo₃ (unknown)

N₂ = Normality of Nacl solution (0.0141)

V₁ = Volume of AgNo₃

V₂ = Volume of Nacl solution (20ml)

Adjust the normality to AgNo₃ to 0.0141N using the relation N₁V₁ = N₂V₂

2. Determination of chloride content in the sample water: Take a suitable volume of sample water (say 50ml) in a conical flask and dilute it to 100ml. with distilled water. Add 1ml k₂cro₄ indicator and titrate with 0.0141N AgNo₃ solution in a PH range of 7-10, to a pinkish yellow end point. Note down the volume of AgNo₃ consumed.

OBSERVATIONS:-

S.No	Burette Readings		Vol. of Titrant used
	Initial	Final

CALCULATIONS:-

                        Chloride content in mg/l = Vol of AgNo₃*N*35450

                                                                     ml of sample water

RESULTS:-

INTERPRETATION OF RESULTS:-