Question

What is the product P?

Answer 1

Silver nitrate solution is used to find out the presence of a halogen in a suspected halogenoalkane. This reaction takes place in the presence of a mixture of ethanol and water i.e. aqueous sodium hydroxide or potassium hydroxide solutions. The silver nitrate test is used to detect the concentration of halide ions.

Complete answer:
The above given reaction is the reaction between an alkyl halide with Silver nitrate solution in the presence of aqueous potassium hydroxide solutions. This reaction is known as the silver nitrate test to detect the presence of halide ions. This test is very sensitive and it is used to detect the concentration of halide ions. This reaction is a type of elimination reaction.
The halogenoalkane is mixed in a mixture of ethanol and water i.e. sodium hydroxide solution $(aq.NaOH)$ or potassium hydroxide solution $(aq.KOH)$ . During this reaction, the halogen atom is displaced as a halide ion.
$R-X+OH^-\xrightarrow{} R-OH+X^-$
Then, the mixture is acidified with a dilute nitric acid solution to prevent the unreacted hydroxide ions reacting with silver ions. Then, the silver nitrate solution is added and various precipitates are formed when the reaction occurs between the silver and halide ions.
$Ag^+(aq)+X^-(aq)\xrightarrow{} AgX(s)$
By observing the precipitate formed, we can distinguish between different types of halide ions.
For example-

Halide Ions present	Observations
$B{r^ - }$	A pale cream precipitate is formed
$C{l^ - }$	A white precipitate is formed
${I^ - }$	A pale yellow precipitate is formed

The general reaction for the given reaction is as follows:
$R-X+AgNO_3\xrightarrow{aq.KOH} R^+NO_3^-+AgX$
Where, $Ag\;X$ is an insoluble precipitate.
$KOH+AgNO_3\xrightarrow{} KNO_3+Ag^++OH^-$
So, the product of the following reaction is:
Hence, the elimination reaction occurs which results in the formation of alkene and indicates the presence of iodide ion as a pale yellow colour precipitate is formed.

Note:
It needs to be remembered that an acidification of the mixture is necessary in order to prevent the unreacted hydroxide ions reacting with silver ions. Always remember that a white precipitate indicates the formation of $Ag\;Cl$ ; a pale cream precipitate indicates $Ag\;Br$ and a pale yellow precipitate indicates $Ag\;I$ . By observing the colour of precipitate, we can distinguish between the halides ions.