The chloride ion is one of the important negative ions found in natural water, and the water acquires a salty taste if it is associated with the sodium ion, forming sodium chloride (table salt). The chloride salts are characterized by their high solubility in water. The presence of chloride ion in a high concentration in the water has a toxic effect in crops, and domestic and industrial water wastes contain a high percentage of chloride. Irrigation water has been classified according to its chloride content into four categories as in the table below:
| Class the water | Chloride concentration mEq / L | The suitability of the water |
| (1) Little | Less than 2 | Water is good for nearly all plants |
| (2) moderate | 2-4 | The water is suitable for plants tolerant of chlorine, with minor to moderate damage visible to plants sensitive to chlorine |
| (3) Medium | 4-8 | The water is suitable for plants that are well tolerant to chlorine, with slight to moderate damage visible to plants less tolerant to chlorine. |
| (4) severe | More than 8 | The water is still suitable for plants that are well tolerated to chlorine, which can show slight to moderate damage |
Mohr’s Method
The correction method (Moore method) is the approved method for determining chloride ion in contaminated water by the American, Indian and Dutch Health Association. It is done by correcting 100 ml of the water sample against a solution of silver nitrate (0.014 cal) and by using the potassium chromate reagent until the color of the sample (light brown) is changed. The results are expressed in mg of chloride liter after taking the average of two readings.
Solutions used:
1. Potassium Chromate K2CrO4 Guide Solution:
It is prepared from dissolving (50gm) of K2CrO4 potassium chromate in a small amount of distilled water. Then drops of AgNO3 silver nitrate solution are added to the solution until a clear red precipitate is formed. The solution was left for 24 hours, then filtered to get rid of the sediment, and the filtrate was diluted to a liter with distilled water.
2. Standard silver nitrate solution (0.0141N):
It is prepared by dissolving 2.395 grams of silver nitrate in a little distilled water, then the volume is supplemented to a liter with distilled water and this solution is kept in dark brown glass bottles.
3. Sodium chloride solution (0.0141N)
Sodium chloride powder is dried at a temperature of (140) degrees Celsius for a period of two hours, after which it is cooled and weighed accurately. 0.8241gm of the dried powder is dissolved with distilled water in a one-liter bottle.
