Question

Two of the substances listed here are highly soluble in water, two are only slightly soluble in water, and two are insoluble in water. Indicate the situation you expect for each one. (a) iodoform, \(\mathrm{CHI}_{3}\) (b) benzoic acid, (c) formic acid, (d) 1-butanol, (e) chlorobenzene, (f) propylene glycol, \(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{OH}\)

Short answer

The highly soluble substances are: formic acid, \( \mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{OH} \). The slightly soluble substances are: iodoform, 1-butanol. Benzoic acid and chlorobenzene are insoluble.

Step-by-step solution

Analyzing Iodoform

Iodoform \(\mathrm{CHI}_{3}\) is a halogen compound. The iodine atoms make the molecule quite large and nonpolar, therefore, though it could have some aqueous solubility, its interaction with water will be limited. Hence, it is slightly soluble in water.

Analyzing Benzoic Acid

Benzoic acid is a carboxylic acid with a large non-polar region (benzene ring). However, it also has an -COOH group which can perform hydrogen bonding with water, hence it is slightly soluble in water despite being predominantly non-polar.

Analyzing Formic Acid

Formic acid is a simple carboxylic acid with two very polar functional groups: the carboxylic acid group and the hydroxyl group. These can easily form hydrogen bonds with water, enhancing its solubility. Thus, formic acid is highly soluble in water.

Analyzing 1-butanol

1-butanol has a polar -OH (alcohol) group that can form hydrogen bonds with water. However, the butyl group \(C_4H_9\) at one end of the molecule is quite large and non-polar. Hence, 1-butanol is slightly soluble in water.

Analyzing Chlorobenzene

Chlorobenzene is a large, predominantly non-polar molecule with a single polar bond due to the presence of Chlorine. Its ability to form hydrogen bonds with water is, however, quite limited. Thus, it is insoluble in water.

Analyzing Propylene Glycol

Propylene glycol \(\mathrm{CH}_{3} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{2} \mathrm{OH}\) has two polar -OH groups that can form hydrogen bonds with water, making it highly soluble in water despite its size.

Key concepts

Iodoform Solubility

Iodoform, with the chemical formula \( \text{CHI}_3 \), is classified as a halogen compound. This means it contains an iodine component, which contributes to its overall structure. The iodine atoms make the molecule quite large, giving it a nonpolar characteristic. Nonpolar molecules generally have weak interactions with water, a polar solvent. As a result, the solubility of iodoform in water is limited, making it only slightly soluble. In essence:

• The large iodine atoms create a nonpolar environment.
• Nonpolar molecules do not mix well with polar ones, such as water.
• Iodoform's solubility in an aqueous solution is therefore minimal.

Benzoic Acid Solubility

Benzoic acid is characterized by the presence of a benzene ring (a large nonpolar structure) and a carboxylic acid group \( (-\text{COOH}) \). While the benzene ring tends to resist dissolving in polar solvents like water due to its nonpolarity, the \( -\text{COOH} \) group can engage in hydrogen bonding. This hydrogen bonding capability enables some degree of interaction with water molecules. Thus, benzoic acid is slightly soluble:

• The \( -\text{COOH} \) group allows hydrogen bonding, promoting some solubility.
• The dominance of the nonpolar benzene limits the extent of solubility.
• Overall, there is a balance that results in slight solubility.

Formic Acid Solubility

Formic acid is a simple carboxylic acid and is notable for its two polar functional groups: the carboxylic acid group and the hydroxyl group. These groups are adept at forming hydrogen bonds with water molecules. Consequently, formic acid is highly soluble in water:

• Both functional groups enhance interaction with water.
• Hydrogen bonds are a primary reason for its notable solubility.
• Its small molecular size further facilitates dissolving in water.

1-Butanol Solubility

1-Butanol is an alcohol, highlighted by its \( -\text{OH} \) group that supports hydrogen bonding. However, its structure also includes a butyl group \( \text{C}_4\text{H}_9 \), which is relatively large and nonpolar. As a result, while it can form some hydrogen bonds with water, the nonpolar butyl component reduces its overall solubility, making it slightly soluble:

• The polar \( -\text{OH} \) group favors limited solubility in water.
• The large nonpolar tail offsets this, restricting full solubility.
• Ultimately, this leads to a balanced, slight solubility in water.

Chlorobenzene Solubility

Chlorobenzene is an organic compound featuring a benzene ring bonded to a chlorine atom. This structural composition renders it largely nonpolar, as the benzene ring constitutes the main part of the molecule. The polar bond arises from the Chlorine's presence, but its ability to engage in hydrogen bonding is minimal. Given these properties, chlorobenzene is insoluble in water:

• The benzene ring's nonpolar nature prevails.
• Limited interaction with water occurs due to insufficient hydrogen bonding.
• This lack of interaction results in insolubility.

Propylene Glycol Solubility

Propylene glycol is distinguished by its structural inclusion of two \( -\text{OH} \) groups. These groups enable the formation of multiple hydrogen bonds with water, capturing the ability to dissolve well. Despite the molecule's relatively larger size, its ample hydrogen bonding opportunities render it highly soluble in water:

• The presence of two \( -\text{OH} \) groups greatly enhances solubility.
• Large potential for hydrogen bonding contributes to mixing with water.
• Size is not a hindrance due to these multiple interactions.