Alternate Tests for Chlorides

The chloride ion is negatively charged and is formed when the element chlorine acquires an electron. Chloride ions are present in extracellular fluid; they are required for the balancing of pressure levels, water, and acid-bases in the body. Chloride is also required for the formation of hydrochloric acid in the stomach. 

An alternate test for chlorides is performed to diagnose conditions such as heart failure, kidney disease, and liver disease. Chloride tests are performed to measure the number of chloride ions in blood and urine. There are different types of alternate tests for chlorides such as the chromyl chloride test, the blood chloride test, the limit test for chloride, tests of chloride with potassium permanganate, the silver nitrate test, and so on.

Chromyl chloride test

The chromyl chloride test is not performed for a solution. It does not give a positive result for silver, mercury, lead, tin, or antimony as because of their covalent nature, they do not generate chloride ions. 

Chromyl chloride is a chemical compound having the formula CrO2Cl2. It is hygroscopic, meaning it absorbs moisture from the air at normal room temperature and is a red, fuming, toxic liquid. Chromyl chloride has a burning odour and is soluble in water. It has a tetrahedral geometry in which the central metal atom (Cr) has the oxidation number +6.

The chromyl chloride test is the best test for the detection of chloride ions in qualitative analysis. This test is highly specific for chloride ions. 

In the chromyl chloride test, a chloride salt is heated with acidified potassium dichromate and concentrated sulphuric acid. If the orange and red vapour of chromyl chloride is obtained, that means the salt is chloride.

CrO2Cl2  +  4NaOH Na2CrO4 + 2NaCl + 2H20

If the chromyl chloride vapour reacts with dilute sodium hydroxide solution, a yellow solution will be obtained due to the formation of sodium chromate. Chlorides are yellow except for silver chromate and mercury chromate, which are red. But we cannot be sure that the formed salt is a chloride. 

To confirm that the salt is a chloride, add the solution to dilute acetic acid and lead (II) acetate solution, and a yellow precipitate of lead chromate will be formed. Thus the salt can be classified as a chloride. 

Blood chloride test 

The blood chloride test is an alternate test for chloride that measures the amount of chloride in your blood or urine. The chloride anion is one of the major electrolytes present in the blood and helps in balancing the amount of fluid in cells. It also helps to maintain proper blood volume, pressure level, and acid-base (pH) balance in your body fluids. 

The blood chloride test is carried out using a syringe to draw a vial of blood from the patient’s arm. The blood collected is then tested for chloride levels.

An alternate blood chloride test is the serum chloride test. This test is performed if a person has symptoms that indicate the body’s fluid level or acid-base balance has been disrupted. The test is most often ordered with other blood tests.

The determination of chloride in human serum or plasma is mainly based on the mercuric thiocyanate method. Chloride is a single ready-to-use reagent in this test. Mix the reagent and sample, incubate for one minute after the aspirate reaction mixture enters the flow cell, and record the absorbance. The typical normal range of blood chloride tests is 96 to 106 milliequivalents per litre (mEq/L) or 96 to 106 millimoles per litre (mmol/L). Normal value scales may vary slightly.

Silver nitrate test for chloride

Another alternate test for chloride anions is the silver nitrate test. Chloride ions are present in table salt, in seawater, on the skin, and in the soil. They cause a problem with submerged objects recovered from the sea, and metals handled uncovered. The easy method for discovering chlorides is by using silver nitrate, which reacts with the chlorides to form a muddy white precipitate. 

To test for chloride ions with the help of silver nitrate, firstly the solution of salt has to be prepared. Add the silver nitrate to the solution, and if chloride ions are present in the solution, a white precipitate will be formed. To confirm the presence of chloride ions, take the white precipitate formed and add it to an ammonia solution. If chloride ions are present in the precipitate, the precipitate will dissolve in the ammonia solution. This confirms the presence of chloride ions in the sample.

AgNO3  + HCL    AgCl (white precipitate) + HNO3

AgCl + 2NH4OH   Ag(NH3)2Cl + 2H2O

Conclusion

An alternate test for chloride ions is generally based on the precipitation of an insoluble chloride salt. 

Chromyl chloride is a chemical compound having the formula CrO2Cl2. It is a hygroscopic, red, fuming, toxic liquid. The chromyl chloride test is the best test for the detection of chloride ions in qualitative analysis. This alternate test for chloride ions is highly specific. 

A chloride test is also used to determine the volume of body fluids. Chlorides are one of the most crucial electrolytes found in the blood. They help to keep the amount of fluid inside cells in balance. They also help to maintain blood volume, blood pressure, and the acid-base (pH) balance of body fluids.