Background Why do aldehydes and ketones behave differently? You will remember that the difference between an aldehyde and a ketone is the presence of a hydrogen atom attached to the carbon-oxygen double bond in the aldehyde. Ketones don't have that hydrogen. The presence of that hydrogen atom makes aldehydes very easy to oxidise.
This is the currently selected item. There are several ways to oxidize aldehydes but perhaps the most fun way is to use Tollen's Reagent. And so we start with an aldehyde here and we add Tollen's reagent which was created by Bernhard Tollens, a German chemist.
Need a source of silver ions, so silver nitrate works well. Need some hydroxide anHines, so sodium hydroxide, and some ammonia. And the order in which you add these and the concentrations will depend on which procedure you're using, but eventually you're gonna form this diamine silver cation here.
And that's going to oxidize your aldehyde to a carboxylate anions, let's go ahead and show the formation of a carboxylate anion here.
So let me go ahead and put in my electrons. So now the carbon has bonded to an oxygen over here on the right, so no longer bonded to a hydrogen, and that's an oxidation, that's an oxidation here. Let's go ahead and draw out some electrons, and let's assign some oxidation states so we know that this is indeed an oxidation reaction here.
So let's put in the electrons in these bonds. So these electrons, right, we know that each bond consists of two electrons, so I'm putting in those electrons in here like that.
One way to assign oxidation Silver mirror experiment is to think about differences in electronegativity. Oxygen is more electronegative than carbon, so we're gonna give all four of those electrons to oxygen, carbon and carbon have the exact same values, so one carbon gets one electron, one carbon gets the other electron.
Between carbon and hydrogen, carbon is more electronegative than hydrogen so it takes those two electrons.
Carbon has four valence electrons and here we have it surrounded by three electrons, so four minus three gives us an oxidation state of plus one.
Over here for our carboxylate anion, let's go ahead and do the same thing here. Let's go ahead and draw everything out, and let's go ahead and use the same color, so we have carbon double bonded to our oxygen, and put in our electrons here, and then we have a carbon bonded to a carbon, and then carbon now bonded to an oxygen over here on the right.
So let's put in our electrons, so we have our electrons in here like that. And once again, think about differences in electronegativity. Oxygen beats carbon, so oxygen gets all four of those electrons, we have a tie between these two carbons.
And then over here now oxygen takes both of those electrons.
So, carbon has four valence electrons, here we have it surrounded by one. So four minus three gives us an oxidation state of, four minus one I should say, gives us an oxidation state of plus three.
And so you can see that our oxidation state has increased: And if you oxidize something you are reducing something else, and that something else is going to be your silver cation here. So we have a silver cation Ag Plus, so an oxidation state of plus one, and since we oxidize our aldehyde we're going to reduce our silver ions, so we're going to reduce it to solid silver with an oxidation state of zero.
So it gains an electron, so this silver cation is reduced to solid silver, and this forms a silver mirror on your glassware if you do everything properly.
So, the formation of a silver mirror indicates the presence of an aldehyde, and so this is a rather cool way, a rather cool diagnostic test for the presence of an aldehyde. And this will help distinguish an aldehyde from a ketone because in general only aldehydes are going to react with a Tollen's reagent, and you get a really cool silver mirror out of it.
If you want to form the carboxylic acid you would need to then protonate your carboxylate anion, and so that would give you your carboxylic acid here.When a satisfactory mirror has formed, wash the solution down the sink with plenty of water.
Rinse out the flask well with water and discard the washings down the sink. Stand your mirror on the line. Place the silver backing edge of your flat mirror on the line you have drawn. Make sure the mirror stands straight and does not move by using clips as shown (you can also tape or rubber band the mirror to a block, or use clothes pens – what ever is at hand Reflection of Light .
Experiment 1 1 Laboratory Experiments for GOB Chemistry _____ I ORGANIC FUNCTIONAL GROUP ANALYSIS I. OBJECTIVES AND BACKGROUND This experiment will introduce you to some of the more common functional groups of organic chemistry. An aldehyde is indicated by the formation of a silver mirror on the wall of the test tube.
Record your. A giant silver mirror experiment Demonstration A solution containing silver nitrate (Tollen’s reagent) and a reducing sugar (glucose) react to form silver, which is deposited as a mirror -like coating on the inside of the reaction vessel.
Tollen’s Test (Silver Mirror) Description: An aldehyde is oxidized by silver (I) to generate a carboxylic acid and silver metal, which coats the surface of the glass vessel.
Materials: M AgNO 3 M KOH M Dextrose Large test tube/rubber stopper Conc. HNO 3 Beaker. Ready-to-go Projects. Just what you need to start work with your ShopBot and begin to learn about the possibilities of CNC. Would you like to submit a project?