Physical Properties of Carboxylic Acids

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Questions and Answers

What is the state of aliphatic carboxylic acids with up to nine carbon atoms at room temperature?

Colourless overboiling liquids with pleasant odours
Colourless solids with pleasant odours
Wax-like solids with strong odours
Colourless liquids with unpleasant odours (correct)

Higher carboxylic acids are usually odourless due to their high volatility.

False (B)

What causes carboxylic acids to have higher boiling points than aldehydes, ketones, and alcohols of comparable molecular masses?

Extensive intermolecular hydrogen bonding

Carboxylic acids with up to four carbon atoms are _____ in water.

miscible Signup and view all the answers

Match the following carboxylic acids with their solubility in water:

Butanoic acid = Miscible in water Hexanoic acid = Slightly soluble in water Octanoic acid = Practically insoluble in water Benzoic acid = Nearly insoluble in cold water Signup and view all the answers

Which of the following statements is true regarding the solubility of higher carboxylic acids?

They are practically insoluble in water due to increased hydrophobic interaction. (D) Signup and view all the answers

Most carboxylic acids exist as monomers in the vapor phase.

False (B) Signup and view all the answers

Flashcards

Physical State of Carboxylic Acids

Carboxylic acids with up to 9 carbon atoms are liquids at room temperature, while those with more carbons are waxy solids.

Boiling Points of Carboxylic Acids

Hydrogen bonding between carboxylic acid molecules is stronger than the hydrogen bonding in aldehydes, ketones, and alcohols of similar size, resulting in higher boiling points for carboxylic acids.

Dimerization of Carboxylic Acids

The strong hydrogen bonds in carboxylic acids persist even in the vapor phase, causing them to form dimers (pairs of molecules) in the gas phase or in solvents that don't form hydrogen bonds.

Solubility of Carboxylic Acids

The ability of a carboxylic acid to dissolve in water decreases as the length of the hydrocarbon chain increases. Short-chain acids (upto 4 carbons) are miscible, while long chains are insoluble.

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Solubility of Benzoic Acid

Benzoic acid is the simplest aromatic carboxylic acid and is poorly soluble in cold water. Aromatic rings are hydrophobic and don't form strong hydrogen bonds with water.

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Carboxylic Acid Solubility in Organic Solvents

Carboxylic acids dissolve in less polar solvents (benzene, ether, alcohol, chloroform) because they can form hydrogen bonds with the solvent molecules.

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Odor of Carboxylic Acids

The unpleasant smells associated with shorter-chain carboxylic acids are due to their volatility. Longer-chain acids have lower volatility and are thus less odorous.

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Study Notes

Physical Properties of Aliphatic Carboxylic Acids

Aliphatic carboxylic acids with up to nine carbon atoms are colorless liquids at room temperature, and have unpleasant odors.
Higher carboxylic acids are waxy solids with low volatility and are practically odorless.
Carboxylic acids have higher boiling points than comparable aldehydes, ketones, and alcohols due to extensive intermolecular hydrogen bonding.
This hydrogen bonding persists even in the vapor phase, where many carboxylic acids exist as dimers.

Solubility of Carboxylic Acids

Short-chain aliphatic carboxylic acids (up to four carbon atoms) are miscible with water due to hydrogen bonding with water molecules.
Solubility decreases with increasing chain length.
Higher carboxylic acids are practically insoluble in water due to strong hydrophobic interactions from their hydrocarbon parts.
Benzoic acid, a simple aromatic carboxylic acid, is nearly insoluble in cold water.
Carboxylic acids are soluble in less polar organic solvents like benzene, ether, alcohol, and chloroform.

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Description

Explore the physical and solubility characteristics of aliphatic carboxylic acids. This quiz covers their state at room temperature, boiling points, and interaction with water, providing insight into their unique properties. Test your knowledge on how chain length affects these substances.