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Chapter 11: Problem 91

The solubility of benzoic acid \(\left(\mathrm{HC}_{7} \mathrm{H}_{5} \mathrm{O}_{2}\right)\),is \(0.34 \mathrm{~g} / 100 \mathrm{~mL}\) in water at \(25^{\circ} \mathrm{C}\) and is \(10.0 \mathrm{~g} / 100 \mathrm{~mL}\) in benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right)\) at \(25^{\circ} \mathrm{C}\). Rationalize this solubility behavior. (Hint: Benzoic acid forms a dimer in benzene.) Would benzoic acid be more or less soluble in a 0.1-M \(\mathrm{NaOH}\) solution than it is in water? Explain.

Short Answer

Expert verified
The solubility of benzoic acid (HC₇H₅O₂) is higher in benzene (a non-polar solvent) compared to water due to the formation of dimers through hydrogen bonding between the carboxyl groups of benzoic acid molecules, which reduces the energy needed to dissolve the solute. In water, benzoic acid forms hydrogen bonds with water molecules, making it less soluble. Benzoic acid would be more soluble in a 0.1 M NaOH solution than in water because NaOH reacts with benzoic acid to form the soluble salt, sodium benzoate (NaC₇H₅O₂), which is much more soluble in water.

Step by step solution

01

Understand the solubility of benzoic acid

Benzoic acid (HC₇H₅O₂) is an organic compound with a relatively polar carboxyl group (COOH) that can form hydrogen bonds. The solubility of benzoic acid in water at 25°C is 0.34 g/100 mL, whereas its solubility in benzene (C₆H₆), a non-polar organic solvent, is 10.0 g/100 mL at the same temperature.
02

Analyze the interaction between benzoic acid and solvents

In order to rationalize the solubility behavior of benzoic acid, we need to analyze the interactions between the solute, benzoic acid, and the solvents (water and benzene). In water, the polar carboxyl group of benzoic acid can form hydrogen bonds with water molecules. In benzene, a non-polar solvent, benzoic acid forms dimers through hydrogen bonding between the carboxyl groups of two benzoic acid molecules.
03

Evaluate the solubility behavior

The solubility of a substance generally depends on the intermolecular forces between the solute and solvent. In this case, the solubility of benzoic acid is higher in benzene compared to water, because the dimerization of benzoic acid (through hydrogen bonding) in benzene reduces the overall energy needed to dissolve the solute. This dimerization does not occur in water, as the polar carboxyl group interacts more strongly with water molecules. So, the solubility of benzoic acid is less in water than in benzene.
04

Compare the solubility in NaOH solution to water

To determine whether benzoic acid would be more or less soluble in a 0.1 M NaOH solution compared to water, we need to consider how NaOH would affect the solubility. NaOH is a strong base and would react with benzoic acid to form a soluble salt, sodium benzoate (NaC₇H₅O₂). The reaction between benzoic acid and NaOH is: HC₇H₅O₂ + NaOH → NaC₇H₅O₂ + H₂O This salt, sodium benzoate, is much more soluble in water. When benzoic acid is in the presence of NaOH, the majority of it would be converted to sodium benzoate, leaving very little benzoic acid undissolved. Therefore, benzoic acid would be more soluble in a 0.1 M NaOH solution than it is in water.

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Most popular questions from this chapter

Calculate the molarity and mole fraction of acetone in a \(1.00-m\) solution of acetone \(\left(\mathrm{CH}_{3} \mathrm{COCH}_{3}\right)\) in ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)\). (Density of acetone \(=0.788 \mathrm{~g} / \mathrm{cm}^{3} ;\) density of ethanol \(=\) \(0.789 \mathrm{~g} / \mathrm{cm}^{3}\).) Assume that the volumes of acetone and ethanol add.

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