Problem 21 - Chemistry: Principles and Reactions

Question

Which of the following is more likely to be soluble in benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) ? In each case, explain your answer. (a) \(\mathrm{CCl}_{4}\) or \(\mathrm{NaCl}\) (b) hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\) or glycerol \(\left(\mathrm{CH}_{2} \mathrm{OHCHOHCH}_{2} \mathrm{OH}\right)\) (c) acetic acid \(\left(\mathrm{CH}_{3} \mathrm{COOH}\right)\) or heptanoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{13} \mathrm{COOH}\right)\) (d) \(\mathrm{HCl}\) or propylchloride \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\right)\)

Step-by-Step Solution

Answer

a) CCl4 or NaCl Answer: CCl4 b) hexane or glycerol Answer: hexane c) acetic acid or heptanoic acid Answer: heptanoic acid d) HCl or propylchloride Answer: propylchloride

Step 1: (a) CCl4 or NaCl

To determine which of these compounds is more likely to dissolve in benzene, we should consider their polarity. Benzene is a nonpolar compound, while CCl4 is also nonpolar, and NaCl is an ionic compound. Since nonpolar substances are likely to dissolve in nonpolar solvents, CCl4 is more likely to be soluble in benzene than NaCl.

Step 2: (b) hexane or glycerol

Hexane (C6H14) is a nonpolar compound as it is an alkane, and glycerol (CH2OH-CHOH-CH2OH) is polar due to the presence of the hydroxyl (-OH) groups. Since benzene is nonpolar, it will have better solubility with hexane, which is also nonpolar, as like dissolves like.

Step 3: (c) acetic acid or heptanoic acid

To determine which of these acids is more likely to dissolve in benzene, we should compare their polarities. Both acetic acid (CH3COOH) and heptanoic acid (C6H13COOH) are carboxylic acids and are polar compounds. However, heptanoic acid has a longer hydrocarbon chain, which makes it less polar than acetic acid. Since benzene is a nonpolar compound, heptanoic acid, which is less polar, is more likely to be soluble in benzene than acetic acid.

Step 4: (d) HCl or propylchloride

In this case, we are comparing HCl, a polar molecule, to propylchloride (CH3CH2CH2Cl), a nonpolar organic compound. Since benzene is nonpolar, propylchloride, which is also nonpolar, will likely be more soluble in benzene as like dissolves like. HCl, being a polar molecule, will not be as soluble in benzene.

Key Concepts

Nonpolar Compounds

Nonpolar compounds are substances in which the electrons are distributed more or less evenly, resulting in little to no charge difference across the molecule. This lack of charge difference means that there are no positive or negative ends in such molecules. Nonpolar molecules typically consist mostly of elements with similar electronegativities.

• Examples of nonpolar compounds include carbon dioxide (\[\text{CO}_2\]), methane (\[\text{CH}_4\]), and nitrogen (\[\text{N}_2\]).
• Benzene (\[\text{C}_6\text{H}_6\]), a classic example of a nonpolar solvent in organic chemistry, effortlessly dissolves nonpolar substances due to the absence of polar interactions.
• It is represented by a hexagonal ring indicating delocalized electrons, resulting in even electron distribution.

Understanding the characteristics of nonpolar compounds is essential because it affects solubility behavior in various solvents, leading to applications in areas like pharmaceuticals, cosmetics, and environmental science.

Like Dissolves Like

The phrase "like dissolves like" is a fundamental principle in chemistry, particularly when discussing solubility. It means that substances with similar polarity tend to dissolve in each other more readily.

• A nonpolar solvent, like benzene, is more likely to dissolve nonpolar substances because there are no significant electrical interactions preventing the solute from dispersing in the solvent.
• Similarly, polar solvents dissolve polar solutes efficiently because of their complementary electrical charges, which attract each other.
• This principle explains why oil and water do not mix; water is polar, and oil is nonpolar.

Understanding this concept helps explain not only why certain substances dissolve together but also it provides insight into how certain processes like extraction and purification work in organic chemistry.

Organic Chemistry

Organic chemistry is an entire field dedicated to studying carbon-containing compounds. This branch of science explores the properties, structures, compositions, reactions, and synthesis of organic compounds, which are made up predominantly of carbon and hydrogen atoms.

• Key concepts in organic chemistry include the study of hydrocarbons such as alkanes, alkenes, and alkynes, which can be either nonpolar or slightly polar.
• An important aspect is the understanding of functional groups, which are specific groupings of atoms that impart certain chemical properties to compounds; examples include alcohols, esters, and carboxylic acids.
• Organic chemistry also explains reaction mechanisms, which describe the step-by-step processes by which chemical reactions occur at the molecular level.

The expertise in organic chemistry is crucial for fields such as pharmaceuticals, where understanding solubility and reactivity of compounds leads to the development of drugs and therapies.

Polarity and Solubility

Polarity refers to the distribution of electric charge around atoms, molecules, or chemical groups. It plays a significant role in determining how substances interact with each other, especially regarding solubility.

• Polar molecules have regions with partial positive and negative charges due to differences in electronegativity between bonded atoms. Water is a prime example of a polar molecule.
• Solubility itself is the ability of a solute to dissolve in a solvent, forming a homogeneous solution. This depends on molecular interactions, such as hydrogen bonding or van der Waals forces.
• In general, polar solutes are expected to dissolve in polar solvents, while nonpolar solutes tend to dissolve in nonpolar solvents, underscoring the importance of "like dissolves like" as a guiding principle.

Knowledge of polarity and solubility helps chemists predict how substances behave in reactions and is fundamental in designing products and processes in chemistry and beyond.