Textbook Question
The figure shows two identical volumetric flasks containing the same solution at two temperatures. (b) Does the molality of the solution change with the change in temperature? [Section 13.4]
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Ch.13 - Properties of Solutions
Chapter 13, Problem 7
The structures of vitamins E and B6 are shown below. Predict which is more water soluble and which is more fat soluble. [Section 13.3]
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Identify the key structural features of vitamins E and B6 that influence their solubility, focusing on the presence of polar (hydrophilic) groups and nonpolar (hydrophobic) regions.
Recall that water solubility is generally associated with molecules containing polar functional groups such as hydroxyl (-OH), amino (-NH2), or phosphate groups, which can form hydrogen bonds with water.
Recognize that fat solubility is favored by large nonpolar hydrocarbon chains or rings, which interact well with lipid environments but poorly with water.
Examine vitamin E's structure for long hydrocarbon chains or aromatic rings that contribute to its nonpolar character, making it more fat soluble.
Examine vitamin B6's structure for multiple polar groups (such as hydroxyl and amino groups) that increase its ability to interact with water, making it more water soluble.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Solubility and Polarity
Solubility depends on the polarity of molecules; polar molecules dissolve well in water (a polar solvent), while nonpolar molecules dissolve better in fats or oils (nonpolar solvents). Understanding the presence of polar groups like hydroxyl or amine groups helps predict solubility.
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Molecular Polarity
Structure and Functional Groups of Vitamins
The chemical structure and functional groups of vitamins determine their polarity. Vitamin B6 contains polar groups such as hydroxyl and amine groups, making it more water soluble, whereas vitamin E has a long nonpolar hydrocarbon chain, increasing its fat solubility.
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Hydrophobic vs. Hydrophilic Interactions
Hydrophobic molecules repel water and tend to dissolve in lipids, while hydrophilic molecules attract water and dissolve in aqueous environments. Recognizing these interactions helps explain why some vitamins are fat soluble (like vitamin E) and others are water soluble (like vitamin B6).
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