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Chapter 22: Problem 118

Is octanoic acid more soluble in \(1 M \mathrm{HCl}, 1 \mathrm{M} \mathrm{NaOH}\), or pure water? Explain. Drugs such as morphine \(\left(\mathrm{C}_{17} \mathrm{H}_{19} \mathrm{NO}_{3}\right)\) are often treated with strong acids. The most commonly used form of morphine is morphine hydrochloride \(\left(\mathrm{C}_{17} \mathrm{H}_{20} \mathrm{CINO}_{3}\right)\). Why is morphine treated in this way? (Hint: Morphine is an amine.)

Short Answer

Expert verified
Octanoic acid is moderately soluble in pure water, but its solubility is limited due to its weak acidic nature and the nonpolar nature of its long hydrocarbon chain. However, it is highly soluble in 1 M NaOH, as the reaction forms sodium octanoate, an ionic compound with strong interactions with polar solvents. In contrast, it is not very soluble in 1 M HCl. Morphine is treated with strong acids like HCl to form morphine hydrochloride, which has a charged ammonium ion. This increases its polarity and solubility in polar solvents like water, making it easier to administer and absorb the drug.

Step by step solution

01

Understand Octanoic Acid and Solubility Rules

Octanoic acid is a carboxylic acid, which means it has a COOH functional group. When carboxylic acids dissolve in water, they tend to ionize to form their conjugate base and H3O+. The solubility of a compound depends on its polarity and the solution it is dissolving in. Generally, the rule of "like dissolves like" applies: polar compounds dissolve in polar solvents, and nonpolar compounds dissolve in nonpolar solvents.
02

Determine the Solubility of Octanoic Acid in 1 M HCl

When octanoic acid is added to a 1 M HCl solution, the hydrogen ion from HCl can protonate the carboxyl group in the octanoic acid. This forms a neutral species which is less soluble in the polar solution than the ionized form. Consequently, octanoic acid is not very soluble in 1 M HCl.
03

Determine the Solubility of Octanoic Acid in 1 M NaOH

When octanoic acid reacts with 1 M NaOH, a strong base, it forms sodium octanoate and water. Sodium octanoate is an ionic compound with high solubility in polar solvents, as it ionizes into cations and anions that can interact with polar molecules in the solvent. Therefore, octanoic acid is highly soluble in 1 M NaOH.
04

Determine the Solubility of Octanoic Acid in Pure Water

When octanoic acid is added to pure water, it can ionize to form H3O+ and its conjugate base. However, as octanoic acid is a weak acid, only a small portion of it will ionize in water, limiting its solubility. Furthermore, the long hydrocarbon chain of octanoic acid is nonpolar, reducing its solubility in the polar water solvent. As a result, octanoic acid is only moderately soluble in water.
05

Why is Morphine Treated with Strong Acids?

Morphine is an amine, meaning it has a nitrogen atom with a lone pair of electrons. When morphine is treated with strong acids, such as HCl, the nitrogen atom can accept a proton from the acid, forming a positively charged ammonium ion in morphine hydrochloride. The formation of the charged ammonium ion increases the polarity of the molecule, enhancing its solubility in polar solvents like water. This makes it easier to administer and absorb the drug, which is why morphine is often treated with strong acids like HCl.

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