Problem 30 - Chemistry The Molecular Nature of Matter

Question

A monofunctional organic oxygen compound dissolves in aqueous base but not in aqueous acid. The compound is in which of the families of organic compounds that we studied? Explain.

Step-by-Step Solution

Answer

The compound is a carboxylic acid because it dissolves in a base by donating a proton to form a soluble salt and does not dissolve in an acid, indicating it can't accept a proton to form a salt.

Step 1: Understanding the Behavior with Aqueous Base

A monofunctional organic oxygen compound dissolves in an aqueous base, which indicates that it is likely to be acidic itself. This is because when an acid reacts with a base, it forms a salt and usually dissolves in water. Therefore, the compound must possess a proton that can be donated to the base, forming a salt that is soluble in the aqueous medium.

Step 2: Understanding the Behavior with Aqueous Acid

The given organic compound does not dissolve in an aqueous acid, which suggests that it does not react with the acid to form a salt. This means that the compound does not act as a base in the presence of acid; hence, it does not possess a functional group that can accept protons readily from the acid.

Step 3: Determining the Family of Organic Compounds

Based on its behavior with an aqueous base and not with an aqueous acid, the organic compound is likely a carboxylic acid. Carboxylic acids possess a carboxyl group (-COOH) that can donate a proton (H+) to a base, forming a carboxylate salt which is water-soluble. This accounts for its solubility in the base and non-solubility in the acid.

Key Concepts

Acid-Base Reactions

Understanding acid-base reactions is essential when studying the solubility of organic compounds. An acid is a substance that can donate a proton (H+ ion), while a base is a substance capable of accepting a proton. The interaction between an acid and a base leads to a neutralization reaction, typically resulting in the production of a salt and water.

Organic compounds containing acidic functional groups, like carboxylic acids, can undergo such reactions. When a carboxylic acid dissolves in an aqueous base, it donates a proton to the base, forming its corresponding carboxylate salt. This salt, being charged, is solubilized in water due to the ion-dipole interactions with water molecules. On the other hand, if the organic compound cannot form a salt with an acid, it indicates that the compound does not contain basic functional groups capable of accepting protons.

This understanding is crucial since it explains the behavior of organic compounds in different environments and helps predict their reactivity and solubility.

Carboxylic Acids

Carboxylic acids are a group of organic compounds defined by their carboxyl (-COOH) functional group. A typical carboxylic acid structure comprises a carbon double-bonded to an oxygen (carbonyl group) and a hydroxyl group (-OH). This arrangement allows the carboxylic acid to act as an acid.

The acidic nature of carboxylic acids is due to the carboxyl group's ability to release a proton, forming a resonance-stabilized carboxylate ion. Because of their acidity, carboxylic acids react with bases to form salts and water, a principle that applies to their solubility as well. In the presence of a base, a carboxylic acid dissolves, forming a water-soluble carboxylate salt. This characteristic is frequently used to separate and identify carboxylic acids from other organic compounds in a mixture.

Furthermore, the solubility of carboxylic acids in water decreases with increasing molecular weight, due to the nonpolar nature of the carbon chain overshadowing the polar carboxyl group's effects.

Functional Groups in Organic Chemistry

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. They are the active sites where chemical reactions occur and largely determine the properties of the organic compounds.

Common functional groups include hydroxyl (-OH), found in alcohols; carbonyl (C=O), which appears in aldehydes and ketones; amino (-NH2), a feature of amines; and the carboxyl (-COOH) group unique to carboxylic acids. Each functional group has a set of properties that influence how the compound behaves chemically. For example, the presence of a carboxyl group in carboxylic acids makes them acidic and soluble in basic solutions, as previously discussed.

Understanding these functional groups is essential for deciphering the reactivity patterns of organic compounds, their solubility, and the types of reactions they can undergo. By looking at the functional group present, chemists can predict the solubility behavior of compounds in different solvents, and design synthesis pathways to create or modify molecules for various applications.