00:01
Hello students in this question we have given four molecules and four tests we have to tell which of these molecules will give a positive test for all of these tests so let me first draw the structures of these molecules acetone is basically ch3 c double bond o ch3 cyclohagenone is cyclohaxin containing a ketone group benzaldehyde is benzene having an aldehyde group like this and three methylbutanal can be drawn something like this.
00:34
This is the structure of 3 methyl butanol.
00:37
Now let me tell you about all these tests, how they are carried out.
00:42
So first of all, iodolform test is used for the confirmation of methyl ketones.
00:48
Now methyl ketone is a specific type of ketone in which one of the alkali groups attached to the c double bond o -carbon is methyl group.
00:57
Now in this test the methyl ketone is reacted with the alkyl -ylle groups.
01:02
Alkaline solution of iodine for example i2 plus n a oh now this reaction will give us the oxidized product of this ketone that is r g double wound o oh plus we will get a c i3 negative anion now after workup this will convert into n a c i 3 now this gets deposited on the surface of test tube in the form of yellow precipitates so formation of yellow precipitates will indicate the presence of a methyl ketone.
01:37
Now one thing is there which you have to remember, one of the alkali group must be methyl groups.
01:45
That's how the ketone will only give the iodofome test.
01:50
Second test is chromic acid test.
01:52
In this test, aldehydes are treated with chromium oxide in the presence of sulfuric acid.
02:00
As a result, this aldehydes get oxidized into herboxylic acid.
02:05
Water is released and we get a chromium 3 sulfate now chromium 3 sulfate 3 is the oxidation state not the number of chromium atoms so this is chromium sulfate and this is a green colored compound so if the solution inside the test tube turns green it will indicate the presence of a aldehyde all type of aldehydes will give a positive test for chromic acid test third test is tolens test it is given positive by the aldehyde compounds in this test ldehyde is treated with tolerance reagent solan's reagent is silver dye ammonia hydroxide now this is the tolerance reagent so reaction of tollen reagent with aldehyde will oxidize the aldehyde into carboxylic acid release some molds of ammonia gas release some molds of water and we will get silver metal as a precipitate.
03:11
Now this silver metal is attached on the test tube's surface and appear as a silver mirror.
03:18
So we will see that a shiny metal has deposited on the walls of the test tube and formation of the shiny silver mirror will indicate the presence of aldehydes.
03:28
Last test is 2 4 dnp test.
03:31
So 2 4 dnp is basically 2 for dynitro phenyl hydrazine...