Tollens' and Benedict's Test - Video Tutorials & Practice Problems

Oxidation Reactions Concept 1

Now, when it comes to Toland's test and Benedict's test, they basically function as oxidation reactions. Now, recall oxidation uses an oxidizing agent to add as many carbon oxygen bonds as possible without breaking any carbon carbon bonds. When it comes to oxidation with Toland's test and Benedict's test, we're paying attention to what's shaded within our box. Now, we're gonna say looking outside that box, initially, we look at alkanes here. We say that alkanes can undergo oxidation to typically make alcohols, alcohols themselves can be oxidized where the carbon with the oh group becomes a carbon group. In this instance, this alcohol gets oxidized into an aldehyde and that aldehyde can undergo further reduction. Remember, we're trying to make as many carbon oxygen bonds as possible to do that. We're gonna have to break one of these carbon hydrogen bonds. So here this is going to be oxidized or removed and in its place, we're gonna have an oxygen placed oxygen needs to make two bonds. So it would be accompanied by a hydrogen. In this instance, we've gone from an aldehyde to a carbolic acid. Now, aldehydes can be oxidized into carbolic acids, ketones because they would have a carbon on both sides, they would not undergo oxidation because remember, we're not trying to break any carbon carbon bonds, we wouldn't be able to break this bond or this bond to add an oxygen to that carb carbon. Right? So here we're just going from an aldehyde to a carbonic acid if we wanted to, we go further on to a carbon dioxide molecule. But again, we're only focusing on this portion or we have an aldehyde being oxidized into a carbolic acid.

Tollens' and Benedict's Test Example 1

Determine which of the following compounds cannot undergo an oxidation reaction. So if we take a look at our choices here, we have Hex Andy Benzal Hyde, Acetone, ethanol and propel. Now, if we take a close look at their names, we see that ad and E and with al meaning that they are aldehydes, remember aldehydes can be oxidized to carboy acids so they can undergo oxidation. Now, B and C Benzal Hyde that is a benzene ring with an aldehyde attached to it. It's in the name aldehyde. Since it's an aldehyde, it can also undergo oxidation to a carbolic acid. The odd one out, the one that cannot undergo oxidation is acetone. Acetone is a common name for a ketone. Remember acetone is ach three group connected to a carbonel group connected to another ch three group. This cannot undergo oxidation because they will require us to cut through carbon carbon bonds which we're not allowed to do under typical oxidation reactions. So here option c would be our correct answer. Acetone cannot undergo an oxidation reaction.

Tollens' Test Concept 2

Now, Tolins tests it tests for the presence of an aldehyde within a basic solution. Here, we're going to say that it's also known as the silver mirror test because of the formation of a silver precipitate. Remember, precipitate just means a solid. Now, here, if we take a look at the reaction for Toland's test, we have a typical aldehyde here and with it, we're reacting it with silver oxide and we have aqueous ammonia, aqueous ammonia just means we have NH three dissolved in water and then we have the addition of heat. This causes my aldehyde to be oxidized into a carbolic acid. During this process, if we have a aldehyde that gets oxidized to a Carboy acid, we'd have the reduction of our silver which would create silver solid. You make a silver solid as a product. Now, in the lab, you're doing this within a test tube. And if your unknown happens to be an aldehyde, the reaction will be successful and give a positive result, the positive result will be the depositing of silver at the bottom, your test tube making it look like a silver mirror. So that's where its name comes from if you were to do this in the lab and you have a test tube, if you have an al as you're unknown, look at the bottom of the test tube, you'll see silver deposits on the bottom, almost reflective. It's a silver mirror. Now, here we're going to say the oxidizing agent can be presented in different ways as a combination of silver. So A G and some type of ammonia. So some type of nitrogen containing compound, right? This is the way I depicted it here, but we'll see other combinations that still qualifies it as being a tolins test. So keep that in mind.

Tollens' Test Example 2

Drawn the carbolic acid produced when 23 dimethyl Pentel is submerged in a Tolins solution. All right. So here we know that Tolins test will change our aldehyde into a carbolic acid. Let's draw what 23 dimethyl pentel would look like. So pent pent means we have five carbons and we're going to say here that al means we have an aldehyde. So we're gonna say that one of the end carbons is an aldehyde carbon. So it's that one and where it's located is one. So 1234 and five, then we have 23 di methyl, those are our substituents. They're located on carbons two and three. So on carbon two, there's a metal in carbon three, there's a metal, this is undergoing a con uh uh oxidation by Toland's test. So remember, it's a combination of silver with some type of ammonia compound. Here, I'm just gonna place o to show that it's being undergoing oxidation. So our aldehyde group will just get oxidized into a carbolic acid. So that would look like this. And then on carbons two and three, we still have our methyl groups. So this would be the carbolic acid formed from the oxidation of our aldehyde by Toland's test.

Benedict's Test Concept 3

Here, we're going to say that like Toland's test, the Benedict test tests for the presence of an aldehyde within a basic solution. So here we're going to say that a positive Benedict test reduces copper two ion to copper one ion in the formation of a brick red, copper one oxide precipitate. Remember, precipitate just means solid. Also remember that brick red is the exact name of the color. You need to remember for a positive Benedict's test. If we take a look here at our equation, we're gonna say under Benedict's test, we have a typical aldehyde. It's gonna be reacting with some copper two basic solution. As a result of this, the aldehyde gets oxidized into a carbolic acid. So here's the formation of our carbolic acid and then we have copper one oxide as a by-product that gives us a brick red color color to our test tube. That would show that we have a positive Benedict test that are unknown somewhere within it had an aldehyde that got oxidized to a carbolic acid. So you'd have cu 20 right. So this would be a generic equation when it comes to the Benedicts test

Benedict's Test Example 3

Here it says, determine the product form when three ethyl hepton now is treated with a basic copper two solution. So remember a basic copper two solution would mean that we're undergoing the Benedict's test and under the Benedict's test, we're just going to oxidize our aldehyde group into a carbolic acid. So this structure for the most part would stay the same or just oxidizing that alde high group into a carbolic acid group. So this represent our product from the oxidation of our aldehyde through the Benedicts test.

Determine the product formed when the following compound undergoes the Benedict's test.

• A.
• B.
• C.
• D. No Reaction

Under the following test, which structure represents the product formed?

• A.
• B.
• C.
• D. No Reaction

What was the starting material that created the following carboxylic acid product?

• A.
• B.
• C.
• D.