Question

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What two chemicals (names and chemical formulas) are mixed with luminol to produce luminescence? 7.

Answer 1

Luminol -

Luminol is a chemical compound with the chemical composition of C₈H₇N₃O₂ , having the chemical structure as follows -

NH2 ΝΗ NH IUPAC - 5-amino-2,3-dihydrophthalazine-1,4-dione Luminol

Luminol shows a special chemical property of chemiluminescence , i.e. , it glows with a blue color when mixed with an oxidizing agent .

Chemiluminescence , the process of emission of light in a chemical reaction .

For example ,

A and B are the reactant and P is the product .

A + B ----> [ transition state ] ----> P + light

Due its property of chemiluminescence , it is used for the forensic investigation , to detect very small amount of blood at the crime scenes , since , it has the capability to react with the iron , which is present in the hemoglobin of the human blood .

Luminol is used as ,

the white powder of the luminol is spread over the area , and then an oxidizing agent is sprayed over it , and surface starts to glow , which can easily be visualized in a dark room .

The oxidizing agent used in this process , is hydrogen peroxide (H₂O₂) along with hydroxide ion (OH ^-) , and the metal ions like iron , copper and cyanide acts as a catalyst .

Luminol itself is not an active compound , hence , it requires an activating agent i.e. the hydrogen peroxide and the hydroxide ion ,

• Firstly the catalyst i.e. the metal ion , iron , reacts with the hydrogen peroxide to release oxygen and water molecules .

• Then , the luminol reacts with the hydroxide ion , to form a dianion , by loosing the acidic hydrogen .
  
  

• The dianion formed then reacts with the oxygen molecule , which forms a very unstable product .

• This unstable product , then rearranges and removes the nitrogen gas to form a triplet dianion species , which is present in an excited state .

• Now, this triplet species , relaxes and comes back to the ground sate and emit energy in the form of blue light which is in the visible region .

And , hence , a blue color luminescence is observed .