Question

Take a few crystals of potassium permanganate in a dry test
tube. Heat the test tube. Bring a glowing incense stick to the
mouth of the test tube. What do you observe?
The stick flares up. What could be the reason?
Does the residue in the test tube have the colour
potassium permanganate?​

Answer 1

Answer:

When you will heat potassium permagnate some vapours will come it is due to the process of convection.

Answer 2

Observation:

=> On heating Potassium Permanganate, which is a strong oxidizer containing manganese in the +7 oxidation state, a gas is seen to be evolved.

=> A glowing splinter bursts into flame and burns brightly as a large concentration of oxygen is produced from the Potassium Permanganate on heating it, this oxygen is a supporter of combustion.

Reason:

=> When any strong oxidizer containing a metal in a higher oxidation state is decomposed: (Eg: K2Cr2O7 or KMnO4)

• Nascent oxygen is formed which eventually forms molecular oxygen.
• one or more compounds containing the same metal in a lower oxidation state are formed.

=> Thus, this reaction also produces oxygen gas, which is a supporter of combustion and relights a glowing splinter or incense stick.

Moving on to the residue:

=> The reaction taking place is:

• KMnO4 --------> K2MnO4 + MnO2 (on strong heating)

=> Here, the oxidation state of Manganese in:

• K2MnO4 (Potassium Manganate) is +6.
• MnO2 (Manganese Dioxide) is +4.

=> Potassium Permanganate is purple in colour and is soluble in water, Potassium Manganate is green in colour and is also soluble in water while MnO2 is black in colour and is insoluble in water.

=> So, if the reaction is completed and water is added, the solution will be green in colour.

=> Hence, the residue will not have the same colour as Potassium Permanganate.