What Is the Solubility of Oxalic Acid Dihydrate?

The solubility of oxalic acid dihydrate (C₂H₂O₄·2H₂O) in water is approximately 90 g/L at 20°C. This value varies with temperature and solvent properties.

Reason:
Oxalic acid dihydrate is highly soluble in water due to its polar nature and ability to form hydrogen bonds with water molecules. The carboxyl groups (–COOH) in oxalic acid interact strongly with water, facilitating dissolution. Additionally, oxalic acid partially ionizes in water, forming hydrogen ions (H⁺) and oxalate ions (C₂O₄²⁻), which further enhances its solubility.

Temperature Dependence of Solubility:

General Trend: The solubility of oxalic acid dihydrate increases with temperature. For example:

At 10°C, solubility is ~60 g/L.

At 30°C, solubility increases to ~120 g/L.

Mathematical Model: The relationship between solubility (S) and temperature (T) can be described using the van't Hoff equation:

lnS=−RΔHsol⋅T1+C

Where:ΔHsolis the enthalpy of solution.

R is the gas constant.

C is a constant.
This model shows that solubility increases exponentially with temperature for many solids, including oxalic acid dihydrate.

Effect of Solvent Properties on Solubility:

Polarity:

Polar Solvents (e.g., Water, Ethanol): Oxalic acid dihydrate dissolves readily due to strong hydrogen bonding and dipole-dipole interactions.

Nonpolar Solvents (e.g., Hexane): Solubility is negligible because nonpolar solvents cannot effectively interact with the polar carboxyl groups.

pH:

Acidic Conditions: In low pH solutions, oxalic acid remains mostly in its molecular form, reducing solubility slightly.

Basic Conditions: In high pH solutions, oxalic acid ionizes completely, forming soluble oxalate ions (C₂O₄²⁻), which significantly increases solubility.

Ionic Strength:

High ionic strength (e.g., in salt solutions) can reduce oxalic acid dihydrate's solubility due to the common ion effect. For example, the presence of oxalate ions from other sources suppresses ionization.

Mechanism of Solubility:

Hydrogen Bonding: The carboxyl groups (–COOH) and water molecules (H₂O) in oxalic acid dihydrate form extensive hydrogen bonds with water, promoting dissolution.

Ionization: Partial ionization in water generates oxalate ions (C₂O₄²⁻), which are highly soluble and stabilize the solution.

Solvent-Solute Interactions: Polar solvents stabilize the dissolved oxalic acid molecules through electrostatic interactions, while nonpolar solvents lack this capability.

The solubility of oxalic acid dihydrate (C₂H₂O₄·2H₂O) in water at 20°C is approximately 10.2 g/100 mL. This value is determined by experimental measurements. At a given temperature, the solubility represents the maximum amount of the solute that can dissolve in a solvent to form a saturated solution. The dissolution process involves the balance between the forces holding the solute particles together and the interactions between the solute and solvent particles.
Solubility change with temperature:
Generally, the solubility of oxalic acid dihydrate in water increases with rising temperature. As the temperature goes up, the kinetic energy of the molecules increases, which helps to break the intermolecular forces in the solid oxalic acid dihydrate more easily and allows more molecules to enter the solution. The relationship between solubility (S) and temperature (T) can often be described by the van't Hoff equation:lnS=−RΔHsol⋅T1+C , where ΔH
sol is the enthalpy of solution, R is the gas constant, and C is a constant.
Effect of solvent properties:
Polarity: Oxalic acid dihydrate is a polar compound. In polar solvents like water, it has good solubility because of the favorable dipole - dipole interactions and hydrogen bonding between the solute and solvent molecules. Non - polar solvents have weak interactions with oxalic acid dihydrate, resulting in low solubility.
Acidity/Alkalinity: In acidic solutions, the ionization of oxalic acid dihydrate is suppressed due to the common - ion effect. This may reduce its solubility. In alkaline solutions, oxalic acid reacts with the base, forming salts (such as oxalate salts), which can increase its solubility as the reaction shifts the equilibrium of dissolution forward.

Oxalic acid dihydrate, or ethanedioic acid dihydrate, exhibits a notable solubility in water. At room temperature (around 20°C), the solubility of oxalic acid dihydrate is approximately 90 grams per liter. This high solubility can be attributed to its molecular structure; the presence of two carboxylic acid groups (-COOH) allows it to form hydrogen bonds with water molecules, facilitating dissolution.

In practical applications, this solubility makes oxalic acid dihydrate useful in various fields. For instance, it serves as an effective cleaning agent for removing rust and hard water stains due to its ability to chelate with metal ions like iron, forming soluble complexes. In household settings, oxalic acid can be found in products designed to clean bathtubs, tiles, and other surfaces prone to mineral deposits or rust stains. Additionally, its use extends to industrial processes where it acts as a bleaching agent for wood, enhancing its appearance by removing unsightly stains caused by exposure to moisture and metals.

When discussing the solubility of oxalic acid dihydrate, it's important to consider several factors. Firstly, temperature significantly affects solubility, with higher temperatures generally increasing the amount of oxalic acid that can dissolve in water. Secondly, caution must be exercised when handling oxalic acid due to its toxicity. Protective measures such as gloves and proper ventilation are necessary during its use. Lastly, disposing of solutions containing oxalic acid requires careful consideration to avoid environmental contamination. Understanding these points ensures safe and efficient utilization of oxalic acid dihydrate across its diverse applications.