Aldehydes, Ketones, and Carboxylic Acids: Important Questions

Very Short Answer Questions [1 Mark Questions]

Ques 1. What is the general formula for aldehydes?

Ans: The general formula for aldehydes is R-CHO.

Ques 2. What type of compound gives the iodoform test?

Ans: The iodoform test can be performed on compounds containing the -CH₃ group.

Ques 3. What is the common name of CH₃CHO?

Ans: The common name of CH₃CHO is acetaldehyde.

Ques 4. Does aldehyde have a higher or lower boiling point than alcohols of comparable molecular masses? Justify your answer.

Ans: Aldehydes have a higher boiling point than alcohols of comparable molecular masses. This is because the carbonyl group in aldehydes can engage in hydrogen bonding while alcohols cannot.

Ques 5. What would be the structure of 3-oxopentanal?

Ans:

Ques 6. How many types of carbonyl groups are there?

Ans: There are two types of carbonyl groups- aldehydes and ketones.

Ques 7. What type of isomerism is shown by CH₃CH₂CHO?

Ans: CH₃CH₂CHO shows constitutional isomerism.

Ques 8. Give an example of a ketone with the maximum number of carbon atoms.

Ans: The ketone with the maximum number of carbon atoms is pentan-2-one.

Ques 9. Which aldehyde is used in the manufacture of perfume?

Ans: Benzaldehyde is used in the manufacture of perfume.

Read More: Aldehydes, Ketones and Carboxylic Acids MCQ

Short Answer Questions [2 Marks Questions]

Ques 1. Place the following in decreasing order or sequence of their acidic power. Also, explain the reason behind your answer.

CH₃CH₂OH, CH₃COOH, CICH₂COOH, FCH₂COOH, C₆H₅CH₂COOH

Ans: The order of acidic power is:

FCH₂COOH > CICH₂COOH > C₆H₅CH₂COOH > CH₃COOH > CH₃CH₂OH

The more powerful the electron-withdrawing substituents, the more powerful the dispersal of the negative charge and, therefore, the stronger the acid will be. 

Ques 2. What type of isomerism is exhibited by acetic acid and ethanol?

Ans: Acetic acid and ethanol both exhibit chain isomerism. This is because they have the same molecular formula but different arrangements of their atoms in space.

Ques 3. Out of propanoic acid and butanoic acid, which is the stronger acid and why?

Ans: Butanoic acid is a stronger acid than propanoic acid. This is because it has a higher molecular mass, which means that there are more electrons available to be donated to the proton.

Ques 4. An organic compound A on treatment with alcoholic KOH gives compound B, which on treatment with dil. HNO₃ yields a colorless gas C and an insoluble solid D. Compound A on ozonolysis yielded two moles of methane. Identify A, B, C & D.

Ans: A is propene, B is propane-2-ol, C is carbon dioxide, and D is calcium carbonate.

Ques 5. Complete the following equations:

CH₃COCH₃ + ______ → CH₃COOH + ______

Ans: CH₃COCH₃ + H₂O → CH₃COOH + H₂

Ques 6. Which is the strongest acid out of the following?

1. HNO2
2. H₂SO3
3. HCN
4. HF

Ans: The strongest acid is HF. This is because it has the smallest and lightest atom as its conjugate base. It also has a high electronegativity, which means that it can easily donate its electrons.

Ques 7. What type of hybridization is present in the carbon atom of acetic acid?

Ans: The carbon atom of acetic acid is sp3-hybridized. This is because it has four different groups attached to it.

Ques 8. What is the IUPAC name of CH₃COOH?

Ans: The IUPAC name of CH₃COOH is acetic acid. With the -oic acid suffix, this indicates that it is a carboxylic acid. The prefix "acet-" tells us that there is a methyl group attached to the carbonyl carbon.

Read More: Aldehyde and ketone general formula

Long Answer Questions [3 Marks Questions]

Ques 1. Ethylbenzene is typically composed of acetylation of benzene followed by reduction and not by direct alkylation. Why?

Ans. The composition of ethylbenzene from acylation of benzene along with reduction is displayed as:

The direct alkylation of benzene is not possible because it would require a very high temperature and pressure to break the strong carbon-carbon bond in benzene. Instead, acetylation of benzene followed by reduction gives ethylbenzene.

Ques 2. Why is carboxylic acid a better leaving group than alcohol in the nucleophilic acyl substitution reaction?

Ans. Carboxylic acids are better-leaving groups than alcohols in the nucleophilic acyl substitution reactions because they are more polarizable. 

This means that the electrons in the carboxylic acid are more easily displaced than those in the alcohol. This makes it simpler for the nucleophile to attack the carbon atom in the carboxylic acid, leading to a higher reaction rate.

Ques 3. Why is acetic acid a more powerful acid than ethanol?

Ans. Acetic acid is a stronger acid compared to ethanol because it has a higher dissociation constant. This means that it is more likely to lose a proton (H⁺) in the solution.

This is because the acetic acid molecule has a higher electronegativity than the ethanol molecule, making it more polar. As a result, the acetic acid molecule is more attracted to water molecules than the ethanol molecule, and this causes it to dissociate more readily.

Ques 4. What type of reaction takes place when a primary amine reacts with acetic anhydride in the presence of pyridine? Give the mechanism of the reaction.

Ans. The type of reaction that happens when a primary amine reacts with acetic anhydride in the presence of pyridine is called Friedel-Crafts acylation. The mechanism of the reaction is displayed below:

Ques 5. What is the general method for the preparation of ketones?

Ans. The general method for preparing ketones is by the oxidation of secondary alcohols. This can be done using several different oxidizing agents, such as potassium permanganate, chromic acid, or Tollens' reagent.

Read More: Acidity Of Carboxylic Acids

Very Long Answer Questions [5 Marks Questions]

Ques 1. What is the nature of the carbonyl group? How is it different from other functional groups?

Ans. The carbonyl group (–C=O) is one of organic chemistry's most important functional groups. It contains a carbon atom double-bonded to an oxygen atom: C=O. The structure of the carbonyl group gives rise to many of the unique properties of ketones and aldehydes.

The carbonyl group is distinguished from other functional groups by several characteristics. 

• First, the carbon and oxygen atoms bond is very strong, making carbonyl compounds more stable than other functional groups. 
• Second, the carbonyl group is planar, meaning that the atoms attached to the carbonyl carbon are arranged in a flat plane. This geometry makes carbonyl compounds very reactive, as the atoms on either side of the carbonyl group can easily interact with other molecules.
• Finally, the carbonyl group is polar, meaning that the electron pushing elements (oxygen and nitrogen) are more electronegative than the carbon atom. This means that the carbonyl carbon is partially negatively charged, while the oxygen is partially positively charged. This polarity gives rise to many of the unique chemical properties of carbonyl compounds.

Ques 2. How do aldehydes differ from ketones?

Ans. Aldehydes and ketones are both carbonyl compounds, meaning that they contain a carbon atom double-bonded to an oxygen atom. The difference between aldehydes and ketones lies in the arrangement of atoms around the carbonyl group.

The carbonyl group is bonded to at least one hydrogen atom in aldehydes. In ketones, the carbonyl group is bonded to two carbon atoms. This difference in structure gives aldehydes and ketones different chemical properties.

Aldehydes are more reactive than ketones because the carbonyl carbon is more electronegative than the carbon atoms it is bonded to. This makes aldehydes more likely to undergo oxidation reactions. 

Ketones are less reactive because the carbonyl carbon is less electronegative than the carbon atoms it is bonded to. Ketones are more stable than aldehydes, meaning they are less likely to undergo chemical reactions.

Ques 3. Alkenes ( C=C ) & carbonyl compounds (C=0) consist of a pie bond. However, alkenes display electrophilic addition reactions. On the other hand, carbonyl compounds display nucleophilic addition reactions. Why?

Ans. The difference in reactivity between alkenes and carbonyl compounds is due to the differences in their electronic structures.

Alkenes have a symmetrical distribution of electrons around the carbon-carbon double bond, while carbonyl compounds have an asymmetrical distribution of electrons around the carbon-oxygen bond. 

This means that the electron density is greater around the oxygen atom in carbonyl compounds than around the carbon atoms in alkenes. As a result, carbonyl compounds are more nucleophilic (electron-rich) than alkenes, and they react with electrophiles (electron-poor species) to form new bonds. 

In contrast, alkenes are more electron-poor than carbonyl compounds, and they react with nucleophiles (electron-rich species) to form new bonds.

Related Links: