Chromyl Chloride Test Mechanism

Chromyl chloride is an inorganic chemical compound. This chemical compound has a reddish-brown colour and can be highly volatile when placed at room temperature. It exists in a liquid form when present at room temperature. This property of chromyl chloride is rather unusual for a transition metal because most of them remain inactive at room temperature. As per the chromyl chloride test mechanism, the compound reacts with water to release hydrochloric and chromic acid. Although these acids are not particularly highly combustible, they can help other chemical substances go through combustion. In the case of combustion caused by chromyl chloride, there should be no contact with water because it will increase the fire instead of slowing it down.

Preparation of Chromyl Chloride

One of the most basic methods for preparing chromyl chloride includes the reaction of chemical compounds such as potassium chromate or potassium dichromate with an acid such as hydrochloric acid. This reaction usually takes place in the presence of sulphuric acid. 

The resultant formed by the chemical reaction goes through distillation so that it can be purified. The presence of sulphuric acid during this process is necessary because it acts as a dehydrating agent. 

Another method for preparing chromyl chloride is exposing chromium trioxide to hydrogen chloride present in the gaseous form. 

This method also detects chloride in any chemical substance. If the chemical compound contains chloride as one of its constituents, it will release red fumes that will give a positive sign of the presence of chloride.

Chromyl Chloride Test Mechanism

Here is an overview of the chromyl chloride test mechanism.

• Potassium dichromate produces chromate trioxide when it comes in contact with sulphuric acid. Chromate trioxide is a dark reddish-brown coloured compound.

K2Cr2O7 + H­2SO4 → CrO3 + H2O

• Next, sodium chloride reacts to sulphuric acid to create sodium bisulphate along with hydrochloric acid.

NaCl +H2SO4 → NaHSO­4 +HCl

• In the final step, chromate trioxide is allowed to react with hydrochloric acid and release chromyl chloride.

CrO3 + HCl → CrO2Cl2

Confirmatory Test for Chromyl Chloride

To confirm the chromyl chloride test mechanism, sodium hydroxide is used. It allows the red vapour to dissolve into it. This is marked by the conversion and formation of a yellow coloured compound.

CrO2Cl2 + NaOH → Na2CrO4 + NaCl +H2O

This is further treated with lead acetate and dilute acetic acid. It forms a yellow precipitate.

CrO42- + Pb(CH3COO)2 → PbCrO4 +CH3COONa

The formation of yellow precipitate means the test mechanism of chromyl chloride is successful.

Exceptions and Alternative Tests

Since the chromyl chloride test does not apply to mercuric, iodide, bromide and silver chlorides, alternative tests are employed to detect the presence of chloride. Here is an example of a chromyl chloride test mechanism for covalent compounds:

• First, the soda extract of the given compounds is prepared. It is treated with silver nitrates which further precipitate out in the form of silver chloride. 
• At the concluding step, sodium arsenate is added, and the test tube is shaken. 
• The formation of a yellow precipitate indicates that the experiment is accurate and there is a presence of chloride ions.

Risks of Chromyl Chloride

Chromyl chloride is very powerful and can irritate the respiratory tract. Inhalation of chromyl chloride can be severe and fatal. It may produce respiratory burns and damage the kidney and liver. The compound also promotes lung cancer and gastrointestinal tract tumours.

Conclusion

We can confirm the presence or absence of chloride ions in a given sample by employing the chromyl chloride test mechanism. However, some substances still cannot be identified and detected by the chrome chloride test. Some elements that cannot be detected for their reaction with chlorine are Hg, Sn, Ag, Pb and Sb. 

These compounds are covalent and cannot form chloride ions. Hence, the test is not acceptable for them. The chromyl chloride test can only be used for the molecules that tend to form ionic bonds.