Where to buy tollens reagent in India?
Tollens reagent is not commercially sold due to its short shelf life. It is freshly prepared in the laboratory during the time of the reaction. Otherwise, chemicals are usually bought from any chemical supplier, manufacture, or third-party dealer in India. This is a trend that has been followed ever since. With the emerging digital age in India, this trend is slowly taking a backseat and making way for digitization for chemical purchase. The digital revolution has started and it is expected to change the way chemical sourcing is done. The on-going COVID-19 pandemic has also contributed to the increasing digitization in the chemical industry to keep the business up and running. Digitization is the new, emerging method of chemical sourcing in India.
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Tollens reagent: Chemical Overview
Tollens reagent is a common chemical reagent with the chemical formula [Ag (NH3)2]NO3. It is used to detect the presence of aldehydes, aromatic aldehydes, and alpha-hydroxy ketone functional group in a given test substance. It was first discovered by a German Chemist Bernhard Tollens, hence, named after him. Tollens reagent is basically a solution of silver nitrate (AgNO3) and ammonia (NH3).
|Freeing point||-10 to -12oC|
|Boiling point||105 to 140oC|
How to make tollens reagent
To prepare tollens reagent, sodium hydroxide is added dropwise to the silver nitrate solution until a brown precipitate is obtained. The brown precipitate is further dissolved with aqueous ammonia. The solution which formed contains the [Ag (NH3)2]+ complex, which form the primary component of tollens reagent.
2AgNO3 + 2NaOH → Ag2O (brown ppt) + 2NaNO3 + H2O
(silver nitrate) (sodium hydroxide) (Soluble sodium nitrate)
Ag2O (brown ppt) + 4NH3 + 2NaNO3 + H2O → 2[Ag (NH3)2]NO3 + 2NaOH
(Con. Ammonia) (Tollens Reagent)
Sometimes, instead of a two-step process, tollens reagent is prepared in a single step. About 2ml of aqueous ammonia is directly added to a solution of 2 ml silver nitrate. Further, to dissolve the precipitate formed, sufficient amount of ammonia solution is added in dropwise until a clear solution is formed.
Uses of tollens reagent
Tollens reagent is popularly used in the laboratory for performing the silver mirror test. The silver mirror test is used to distinguish aldehydes from ketones, where the former gives a positive silver mirror test and the later a negative test. Tollens reagent acts as a mild oxidizing agent and oxidizes aldehydes to acetate ion, where the silver ion is reduced to metallic silver. A bright silver mirror is formed inside the test tube (or the container), or sometimes it also appears as a greyish-black precipitate. The formation of silver mirror indicates the presence of aldehydes in the chemical compound.
Toxicity of tollens reagent
Tollens reagent is associated with toxic effects; therefore, it has to be handled with care. It is recommended to wash hands thoroughly after handling it. It is harmful when swallowed, hence, it is important to get the necessary medical help immediately. In contact with the skin, it causes skin irritation. On mild contact with the skin, it is advised to wash with soap and plenty of water. If the irritation persists even after washing, getting medical attention becomes necessary. Tollens reagent causes serious eye irritation, hence, when you experience the chemical contact with eyes, wash your eyes thoroughly with water and rush to the nearest clinic.
First aid measures
- In the event of skin contact, take off the contaminated clothes and wash the exposed skin with soap and water.
- When you experience contact with eyes, remove the contact lenses (if applicable) and continue rinsing using clean hands. Keep rinsing until you feel better. Seek medical attention if needed.
- In case you ingested tollens reagent, rinse your mouth and seek medical help. Inducing vomiting is not advised.
Accidental spillage of the chemical should be cleaned thoroughly to avoid contact with the other personnel working in the laboratory. The spillage should be collected and disposed in the suitable containers. If the spillage is more, soak up the spills with inert solids such as clay as soon as possible. Leave it for a few minutes and clean it up wearing necessary personal protective equipment (PPE), and dispose of in the suitable container.
Handling and Storage
When preparing and dealing with tollens reagent, ensure to wear the necessary PPE. Try to avoid contact with skin, eyes and clothing. Wash hands and other exposed areas with mild soap and water before eating, drinking, and while leaving from the laboratory.
Due to short shelf life, it is often prepared only when required. The storage is not applicable for tollens reagent in most of the case. Rarely when stored, it should be kept in a closed container in a cool dry place away from the sunlight.