Rank the following molecules from least water soluble to most water soluble. Explain your reasoning.
(e) CH₃CH₂CH₂CH₂CH₃

Verified step by step guidance

Step 1: Understand the concept of water solubility. Water solubility is influenced by the ability of a molecule to form hydrogen bonds with water. Molecules with polar functional groups or those capable of hydrogen bonding are generally more water-soluble than nonpolar molecules.

Step 2: Analyze the structure of the given molecule, CH₃CH₂CH₂CH₂CH₃. This molecule is a straight-chain alkane (pentane) with no polar functional groups or atoms capable of hydrogen bonding. It is entirely nonpolar.

Step 3: Compare the solubility of CH₃CH₂CH₂CH₂CH₃ to other molecules (if provided in the problem). Nonpolar molecules like alkanes are generally less water-soluble than polar molecules or those with functional groups such as hydroxyl (-OH), carbonyl (C=O), or amine (-NH₂).

Step 4: Consider the size of the molecule. Larger nonpolar molecules tend to be even less water-soluble because their hydrophobic nature increases with size, making it harder for water to interact with them.

Step 5: Rank the molecules based on their polarity and ability to interact with water. Since CH₃CH₂CH₂CH₂CH₃ is nonpolar and lacks functional groups for hydrogen bonding, it would likely rank as one of the least water-soluble molecules in the list.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Polarity of Molecules

Polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, which have a significant difference in electronegativity between atoms, tend to dissolve well in water due to their ability to form hydrogen bonds. In contrast, nonpolar molecules, which have an even distribution of charge, do not interact favorably with water, leading to lower solubility.

Hydrophobic vs. Hydrophilic

Hydrophobic molecules are water-repelling and typically consist of long hydrocarbon chains, while hydrophilic molecules are water-attracting and often contain polar functional groups. The solubility of a molecule in water is influenced by its hydrophobic or hydrophilic nature; molecules with more hydrophilic characteristics will generally be more soluble in water than those that are hydrophobic.

Chain Length and Solubility

The length of a hydrocarbon chain affects its solubility in water. As the chain length increases, the hydrophobic character of the molecule becomes more pronounced, leading to decreased solubility in water. For example, longer alkanes like CH₃CH₂CH₂CH₂CH₃ (pentane) are less soluble in water compared to shorter, more polar molecules due to their larger nonpolar surface area.

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