Question

Would benzoic acid be more or less soluble in a \(0.1-M \mathrm{NaOH}\) solution than it is in water?

Short answer

Benzoic acid will be more soluble in a 0.1M NaOH solution than in water, as it reacts with NaOH to form the highly soluble sodium benzoate salt (C6H5COONa).

Step-by-step solution

Write the chemical reaction between benzoic acid and NaOH.

First, we need to write the chemical reaction between benzoic acid (C6H5COOH) and sodium hydroxide (NaOH): \[ C6H5COOH + NaOH \rightarrow C6H5COONa + H2O \] In this reaction, benzoic acid donates a proton to NaOH, forming the sodium benzoate salt (C6H5COONa) and water (H2O).

Determine the solubility of benzoic acid in water.

Benzoic acid has a solubility of approximately 1.7g per 100ml of water at 20°C. This value can vary slightly depending on the temperature and purity of the benzoic acid.

Determine the solubility of sodium benzoate in water.

Sodium benzoate, the salt formed by the reaction of benzoic acid with NaOH, is much more soluble in water than benzoic acid. Its solubility in water is approximately 62g per 100ml of water at 20°C.

Compare the solubility of benzoic acid in water with its solubility in NaOH solution.

Since benzoic acid reacts with NaOH to form the highly soluble sodium benzoate salt, the solubility of benzoic acid in the 0.1M NaOH solution will increase as it is converted into sodium benzoate. Therefore, benzoic acid will be more soluble in the 0.1M NaOH solution than it is in water.

Key concepts

Benzoic Acid

Benzoic acid is an aromatic carboxylic acid with the chemical formula \( C_6H_5COOH \). It is composed of a benzene ring bonded to a carboxylic acid group. This compound is known for its role as a precursor in the synthesis of many organic substances. Benzoic acid is a solid at room temperature and is slightly soluble in water.
Its solubility is approximately 1.7g per 100ml of water at 20°C, which is relatively low. This low solubility is mainly due to the hydrophobic benzene ring that does not interact favorably with water molecules. However, the carboxylic acid group can donate a proton, making benzoic acid able to react with bases, such as sodium hydroxide, to form water-soluble salts.

Sodium Hydroxide

Sodium hydroxide, often referred to by its chemical formula \( ext{NaOH} \), is a strong base widely used in various chemical processes. It is a white, solid ionic compound that dissolves readily in water, releasing hydroxide ions \( ( ext{OH}^-) \). This reaction is highly exothermic, which means it releases a considerable amount of heat as it dissolves.
In a solution, sodium hydroxide acts as a source of hydroxide ions that can accept protons from acids. This makes it an excellent reagent for proton exchange reactions, such as the neutralization of acidic compounds like benzoic acid. When \( ext{NaOH} \) reacts with benzoic acid, it converts the acid into a salt, sodium benzoate, which is significantly more soluble in water.

Sodium Benzoate

Sodium benzoate is the sodium salt derived from benzoic acid. Its chemical formula is \( ext{C}_6 ext{H}_5 ext{COONa} \). This compound is formed when benzoic acid reacts with a base, such as sodium hydroxide. In this interaction, benzoic acid donates a proton to the base, resulting in the formation of sodium benzoate and water.
Unlike benzoic acid, sodium benzoate is highly soluble in water. Its solubility is about 62g per 100ml of water at 20°C. This significant increase in solubility arises because the ionic nature of sodium benzoate interacts strongly with water molecules, allowing it to dissolve more readily. As a result, benzoic acid, when converted into sodium benzoate, can dissolve in much higher concentrations.

Chemical Reaction

The reaction between benzoic acid \( ( ext{C}_6 ext{H}_5 ext{COOH}) \) and sodium hydroxide \( ( ext{NaOH}) \) is an example of an acid-base neutralization reaction. In this reaction, the acidic benzoic acid donates a proton \( ( ext{H}^+) \) to the hydroxide ion from sodium hydroxide. The products of this reaction are sodium benzoate \( ( ext{C}_6 ext{H}_5 ext{COONa}) \) and water \( ( ext{H}_2 ext{O}) \).
This chemical reaction not only neutralizes the acid but also increases the solubility of the benzoic acid in the solution by converting it into a more soluble salt. The overarching principle driving this reaction is the tendency of the system to achieve a more stable, lower energy state by forming water and the ionic compound sodium benzoate.

Solubility Comparison

Solubility comparison is an essential concept in chemistry, particularly when examining how different substances dissolve in various solvents. In the case of benzoic acid and sodium benzoate, we see a marked contrast in their solubility in water. While benzoic acid is only slightly soluble in water, sodium benzoate, the result of its reaction with sodium hydroxide, is much more soluble.
By reacting benzoic acid with a base like sodium hydroxide, we can dramatically increase the solubility. This is because the reaction forms sodium benzoate, which, due to its ionic nature, interacts much more favorably with water molecules. Therefore, benzoic acid is more soluble in a sodium hydroxide solution than it is in pure water, because it is converted into the highly soluble sodium benzoate.