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Aldehydes, Ketones & Carboxylic Acids Class 12 Notes Chemistry Chapter 8

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FAQs on Aldehydes, Ketones & Carboxylic Acids Class 12 Notes Chemistry Chapter 8

1. What are the common properties and uses of aldehydes, ketones, and carboxylic acids?
Ans. Aldehydes, ketones, and carboxylic acids are organic compounds that share similarities in their chemical properties. They all contain a carbonyl group, which is a carbon atom double-bonded to an oxygen atom. Aldehydes have the carbonyl group at the end of a carbon chain, ketones have it in the middle, and carboxylic acids have it at the end of a carbon chain with an attached hydroxyl group. Common properties of aldehydes, ketones, and carboxylic acids include: 1. Polar nature: The carbonyl group makes these compounds polar, allowing them to form hydrogen bonds with other molecules. 2. High boiling points: Aldehydes, ketones, and carboxylic acids have higher boiling points compared to hydrocarbons of similar molecular weight due to intermolecular forces. 3. Solubility in water: Small aldehydes and ketones are soluble in water due to hydrogen bonding, while carboxylic acids can form strong hydrogen bonds with water. 4. Strong odors: Many aldehydes and ketones have distinct smells and are commonly used in perfumes and flavors. 5. Reactivity: Aldehydes, ketones, and carboxylic acids undergo various chemical reactions, such as oxidation, nucleophilic addition, and condensation reactions. These compounds find applications in various industries, including pharmaceuticals, food additives, solvents, and polymer production.
2. What is the difference between aldehydes and ketones?
Ans. Aldehydes and ketones are both organic compounds that contain a carbonyl group (-C=O), but they differ in their molecular structure and placement of the carbonyl group. The main difference between aldehydes and ketones is the position of the carbonyl group within the carbon chain. In aldehydes, the carbonyl group is located at the end of a carbon chain, while in ketones, it is found in the middle of the chain. This structural difference leads to variations in their physical and chemical properties. Aldehydes tend to have a stronger odor compared to ketones, and they are more easily oxidized. Ketones, on the other hand, have higher boiling points and are more stable than aldehydes. Both aldehydes and ketones find applications in various industries, including the production of solvents, pharmaceuticals, and flavors.
3. How do carboxylic acids differ from aldehydes and ketones?
Ans. Carboxylic acids, aldehydes, and ketones are all organic compounds containing a carbonyl group (-C=O). However, carboxylic acids have an additional functional group called a carboxyl group (-COOH), which consists of a carbonyl group bonded to a hydroxyl group (-OH). The presence of the carboxyl group gives carboxylic acids distinct properties compared to aldehydes and ketones: 1. Acidic nature: Carboxylic acids are weak acids and can donate a proton (H+) to form a carboxylate ion (-COO-). 2. Higher boiling points: Carboxylic acids have higher boiling points compared to aldehydes and ketones of similar molecular weight due to the presence of intermolecular hydrogen bonding between carboxylic acid molecules. 3. Solubility in water: Carboxylic acids are generally soluble in water due to the ability to form hydrogen bonds with water molecules. 4. Strong odor: Some carboxylic acids have strong, pungent odors. For example, acetic acid gives vinegar its distinctive smell. Carboxylic acids find applications in various fields, including food preservation, pharmaceuticals, and the production of polymers and esters.
4. How are aldehydes and ketones named?
Ans. The naming of aldehydes and ketones follows specific rules based on the IUPAC (International Union of Pure and Applied Chemistry) system. For aldehydes: 1. The parent chain is selected, and the suffix "-al" is added to the root of the corresponding alkane name. 2. The carbon in the carbonyl group is assigned the number 1, and the other carbon atoms are numbered accordingly. 3. The substituents attached to the aldehyde carbon are named as prefixes, indicating their position and nature. 4. If there is only one substituent, it is named as a prefix before the parent chain name. For example, formaldehyde (HCHO) is named as methanal, acetaldehyde (CH3CHO) as ethanal, and benzaldehyde (C6H5CHO) as benzenecarbaldehyde. For ketones: 1. The parent chain is selected, and the suffix "-one" is added to the root of the corresponding alkane name. 2. The carbon atoms in the carbonyl group are assigned the lowest possible numbers, and the other carbon atoms are numbered accordingly. 3. The substituents attached to the ketone carbon atoms are named as prefixes, indicating their position and nature. For example, acetone (CH3COCH3) is named as propanone, and butanone (CH3COCH2CH3) is named as 2-butanone.
5. How can aldehydes and ketones be distinguished using Tollens' test and Fehling's test?
Ans. Tollens' test and Fehling's test are commonly used to distinguish between aldehydes and ketones based on their ability to undergo oxidation. Tollens' test: 1. Tollens' reagent is prepared by dissolving silver nitrate (AgNO3) in ammonia (NH3) until a clear solution is formed. 2. The aldehyde or ketone to be tested is mixed with Tollens' reagent and heated in a water bath. 3. If an aldehyde is present, it reduces the silver ions in Tollens' reagent, forming a silver mirror on the inner wall of the test tube. Ketones do not react with Tollens' reagent. Fehling's test: 1. Fehling's solution is prepared by mixing equal parts of Fehling's A (copper(II) sulfate) and Fehling's B (sodium potassium tartrate and sodium hydroxide) solutions. 2. The aldehyde or ketone to be tested is mixed with Fehling's solution and heated in a water bath. 3. Aldehydes are readily oxidized by Fehling's solution, resulting in the formation of a brick-red precipitate of copper(I) oxide. Ketones do not react with Fehling's solution. These tests rely on the fact that aldehydes are easily oxidized to carboxylic acids, while ketones are more resistant to oxidation.
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