This method is applicable to measurement of chloride in natural water, boiler water and cooling water. The measuring scope of chloride (chloride ion)is 5 ~ 100 mg/L, when it is more than 100 mg/L, the volume of the sample can be appropriately reduced, then the sample can be diluted to 100ml, and then the sample can be measured. 

1. Summary of the methods: With potassium chromate as indicator, under neutral or weak alkali conditions, the water sample is tested by titration of  standard solution of silver nitrate, when brick red silver chromate precipitates,  which indicates the end points arrives. Reaction is as follows:   Cl-+Ag+→AgCl↓           （white）

        CrO42-+2Ag+→Ag2CrO4-↓  （brick-red）

2. Reagent:

 (1) 1% phenolphthalein indicator.

 (2) 10% potassium chromate indicator. 

(3) 0.1 mol/L or 0.05 mol/L sulfuric acid solution.

(4) 0.1 mol/L sodium hydroxide solution. 

(5) Solid reagents of sodium chloride.

(6) 1ml standard solution of silver nitrate is equivalent to 1.0 mgCl. 

3. Analysis steps:

 (1) Use a pipette to accurately absorber 100 ml water sample in a 250 ml conical flask, add 2 ~ 3 drops of phenolphthalein indicator, if the water sample appears red, use 0.1 mol/L sulfuric acid solution to neutralize it until it becomes colorless; If the red color does not appear red, then use 0.1 mol/L sodium hydroxide solution to neutralize the water sample to red, and then use 0.1 mol/L sulfuric acid solution for titration until the solution is just colorless. 

(2) Use 1 ml potassium chromate indicator, use standard solution of silver nitrate (1 ml is equivalent to 1mgCl-1) for tritration to orange, write down the consumption(a) of standard solution of silver nitrate . At the same time, do  the blank test and write down the consumption(b) of standard solution of silver nitrate. 

(3) If the chloride ion content in water samples is more than 100 mg/L, it is possible to take less water sample and use the reagent water to dilute the water sample to 100 ml, then carry out the test according to the procedures mentioned in Section 3.1 and 3.2.

4. Calculation:  

The chloride content in water sample  (Cl -) is calculated according to the following formula: 

X = (a - b) T/Vx 1000           

Where:

a - Consumption of standard solution of silver nitrate for titration of water sample, ml. 

b -  Consumption of standard solution of silver nitrate when the blank test is done, ml. 

T -  Titre of standard solution of silver nitrate, mg/ml. 

V -  Volume of water sample taken for titration, ml. Note: 1000-1000 ml/L.