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Ch.13 - Solutions
Chapter 13, Problem 31

Which molecule would you expect to be more soluble in water: CH3CH2CH2OH or HOCH2CH2CH2OH?

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1
Identify the functional groups in each molecule. CH3CH2CH2OH has an alcohol group (-OH) attached to a propyl group, while HOCH2CH2CH2OH has an alcohol group at both ends of a propane chain.
Consider the polarity of the molecules. Molecules with higher polarity are generally more soluble in water, which is a polar solvent.
Assess the ability of the molecules to form hydrogen bonds with water. Hydrogen bonding significantly enhances solubility in water.
Compare the number of hydroxyl groups (-OH) in each molecule. More hydroxyl groups typically increase the hydrophilicity (water-loving nature) of the molecule.
Conclude which molecule is more likely to be soluble in water based on the presence of more hydroxyl groups and the overall polarity.

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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 their atoms, tend to interact favorably with water, a polar solvent. In contrast, nonpolar molecules do not dissolve well in polar solvents due to their lack of charge separation.
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Hydrogen Bonding

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen or nitrogen. Molecules capable of forming hydrogen bonds with water can enhance their solubility. The presence of hydroxyl (-OH) groups in a molecule increases its ability to form hydrogen bonds with water.
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Hydrophobic vs. Hydrophilic Interactions

Hydrophobic interactions occur between nonpolar molecules that repel water, while hydrophilic interactions involve polar or charged molecules that attract water. Molecules with long nonpolar hydrocarbon chains are typically hydrophobic, reducing their solubility in water. In contrast, molecules with more polar functional groups are hydrophilic and tend to dissolve better in aqueous environments.
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