Question

Choose the incorrect statement: (A) Methanal is gas and ethanal is volatile liquid at room temperature (B) Some aldehyde and ketone as methanal, ethanal and propanone are soluble in water (C) Aldehydes and ketones are used in blending of perfumes (D) Aldehydes and ketones are insoluble in organic solvents such as chloroform

Short answer

The incorrect statement is (D) "Aldehydes and ketones are insoluble in organic solvents such as chloroform". In fact, they are soluble in many organic solvents, including chloroform, due to their polar carbonyl group that allows them to form dipole-dipole interactions with other polar molecules.

Step-by-step solution

Evaluate Statement (A)

Methanal (formaldehyde) is an aldehyde with the formula HCHO, and ethanal (acetaldehyde) is another aldehyde with the formula CH3CHO. Methanal is a gas at room temperature, while ethanal is a volatile liquid. Therefore, statement (A) is a correct statement.

Evaluate Statement (B)

Methanal, ethanal, and propanone (acetone) are common examples of aldehydes and ketones, and all three are soluble in water. This is due to their ability to form hydrogen bonds with water molecules. Therefore, statement (B) is also a correct statement.

Evaluate Statement (C)

Aldehydes and ketones are known for their characteristic odors, and due to this property, they are often used in the blending of perfumes and in the fragrance industry. Statement (C) accurately states this application of aldehydes and ketones and is a correct statement.

Evaluate Statement (D)

The statement claims that aldehydes and ketones are insoluble in organic solvents such as chloroform. However, this statement is incorrect. Aldehydes and ketones are soluble in many organic solvents due to their polar carbonyl group, allowing them to form dipole-dipole interactions with other polar molecules. They are particularly soluble in polar aprotic solvents like chloroform. The incorrect statement is (D).

Key concepts

Chemical Properties of Aldehydes and Ketones

Aldehydes and ketones are organic compounds characterized by the presence of a carbonyl group (C=O). This group highly influences their chemical properties. Aldehydes have the carbonyl group at the end of the carbon chain, making them quite reactive.
Methanal (formaldehyde) and ethanal (acetaldehyde) are examples of aldehydes known for their reactivity. For instance, methanal is a gas at room temperature, while ethanal is a volatile liquid.

Ketones, on the other hand, have the carbonyl group within the carbon chain, which generally makes them less reactive than aldehydes. Propanone (acetone) is an example of a ketone that is commonly used due to its relatively lower reactivity compared to aldehydes.

• Aldehydes are more reactive due to their terminal carbonyl group.
• Both aldehydes and ketones can undergo reactions such as nucleophilic addition.
• They can form hydrogen bonds with water, leading to solubility in it.

These properties make aldehydes and ketones versatile in various chemical reactions and applications.

Solubility in Water

A fascinating property of aldehydes and ketones is their solubility in water. The solubility is due to the presence of the carbonyl group, which allows these molecules to form hydrogen bonds with water molecules. This leads to the solubility of smaller molecules like methanal, ethanal, and propanone in water.
As the carbon chain length increases, the hydrophobic nature of the hydrocarbon chain becomes more prominent, reducing solubility. This means that larger aldehydes and ketones are less soluble or even insoluble in water.

• Small molecules (like methanal, ethanal, and propanone) are soluble due to hydrogen bonding.
• Larger molecules have reduced solubility as the hydrophobic chain overrides the carbonyl's hydrophilic nature.

Understanding these solubility trends is essential in predicting how different aldehydes and ketones will behave in aqueous solutions.

Uses in Perfumery

Aldehydes and ketones are widely used in the fragrance industry due to their distinct odors. They are critical in creating perfumes and scented products, thanks to their ability to blend well with aromatic compounds, enhancing or modifying scents.
In perfumery, aldehydes and ketones can act as aromatic enhancers, blending in to create unique fragrances. For instance, the aldehyde C12 (also known as lauric aldehyde) is famous for its floral and citrusy note, used in various high-end perfumes.

• Aldehydes contribute to fresh, bold scents.
• Ketones can add depth and complexity to fragrances.
• Both are capable of mellowing or amplifying existing scents in a blend for desired results.

Through their application, these compounds are integral to developing a vast array of fragrances, offering an ever-expanding world of olfactory experiences.