Question

neaili CUIUILOT 4. How do you testing of formaldehyde? 5. What health hazards of health hazards?

Answer 1

Tollens test is a laboratory test that is widely used to test the presence of aldehyde groups.

This is also called as silver mirror test and is also capable to differentiate between aldehyde and ketone.

The test is done as follows

1. Silver nitrate (in water) is mixed with sodium hydroxide followed by addition of aq. ammonia until the precipitated silver oxide is dissolved completely. The reaction is shown as below.

2AgNO₃ + 2NaOH $\rightarrow$ Ag₂O + 2NaNO₃ + H₂O

Ag₂O + 4NH₃$\rightarrow$ 2Ag(NH₃)₂⁺ + OH^-

The Tollens reagent thus formed can easily oxidize the formaldehyde into formic acid by reducing the silvercation into metallic silver.

HCHO + 2Ag⁺ +2 OH^-  $\rightarrow$ HCOOH + 2Ag + H₂O

If the test is carried out in a glass tube (clean surface) we can observe the metallic silver getting deposited to the sides of glass tubes appearing as a mirror.