Oxalic Acid

Oxalic acid is a dicarboxylic acid having chemical formula C₂H₂O₄. It is called as Ethanedioic acid. Oxalic acid is found in many vegetables and plants. It is the simplest dicarboxylic acid having HOOC-COOH and has an acidic strength greater than acetic acid.

In this article, we will learn about, the Oxalic Acid Formula, Equivalent Weight of Oxalic Acid, Structure of Oxalic Acid, Properties of Oxalic Acid, Preparation of Oxalic Acid, and others, in detail.

What is Oxalic Acid?

Oxalic acid is a dicarboxylic acid. This means in Oxalic Acid two carboxylic acids are connected to each other with a single covalent bond. It is a crystalline white power and its solution is colorless in nature. Its structure is HCOOH-HCOOH, and its condensed form is, C₂H₂O₄. The image added below shows the crystalline form and colorless solution of the oxalic acid.

👁 oxalic Acid Structure

Oxalic Acid Formula

Oxalic acid is a strong dicarboxylic acid in nature which is much more acidic in than acetic acid. Oxalic Acid contains Carbon(C), Hydrogen(H), and Oxygen(O) in the ratio of 1:1:2. It is the simplest dicarboxylic acid containing only two carboxylic acids directly bonded to each other at carbon atoms, i.e. (COOH) groups. The chemical formula of Oxalic Acid is HOOC-COOH, and it is also represented as (COOH)₂ or C₂H₂O₄.

Molar Mass of Oxalic Acid

Molar Mass is the total mass of the molecule present in a one-mole substance and is equivalent to the atomic weight of the substance. Carbon, Hydrogen, and Oxygen have molar masses of 12 gm/mole, 1 gm/mole, and 16 gm/mole respectively, and one molecule of oxalic acid contains two atoms of Carbon, two atoms of Hydrogen, and four atoms of Oxygen. Thus the molar mass of oxalic acid is 2×12 + 2×1 + 4×16 i.e.,  90 grams per mole.

Note: Molecular Weight of Oxalic Acid is 90 amu

The structure of Oxalic Acid is added in the image below,

👁 Oxalic Acid

Equivalent Weight of Oxalic Acid

Equivalent weight of hydrated Oxalic acid (C₂H₂O₄ .2H₂O) is 126 amu (90 + 2×18) and the valency (number of hydrogen ions released by it when dissociated) is 2. It is also called the basicity of Oxalic Acid. Thus, the basicity of Oxalic Acid is 2.

Equivalent weight is given by the formula,

Equivalent Weight = (Molecular Weight)/(Valency)

So, the equivalent weight of hydrated oxalic acid is = 126/2 = 63

Thus, the equivalent weight of Oxalic acid is 63.

Oxalic Acid Structure(C₂H₂O₄)

Oxalic acid is a dicarboxylic acid and its structure consist of two -COOH group attached together as shown in the diagram added below,

👁 Oxalic acid Structure

Preparation of Oxalic Acid(C₂H₂O₄)

Although oxalic acid is readily available in nature and can be extracted from different means, but also oxalic acid can be made in the laboratory by oxidizing sucrose with nitric acid in the presence of a small amount of vanadium pentoxide as a catalyst. The hydrated solid can be dehydrated by heat or azeotropic distillation.

Procedure of Preparation of Oxalic Acid

Oxalic Acid can be prepared by following steps:

Step 1: Take the watch glass, wash it with distilled water, and let it dry.  

Step 2: Weigh the exact amount of clean and dry watch glass and record its weight in a notebook. 

Step 3: Correctly weigh 3.15 g of oxalic acid on a  watch glass and write down this weight in a notebook.  

Step 4: Using a  funnel, gently and carefully transfer oxalic acid to a clean, dry volumetric flask from the watch glass. 

Step 5: Wash the watch glass with distilled water and use a wash bottle to wash away the particles adhering to the watch glass with foam. For completing the experiment, the amount of water should not exceed 50 ml.

Step 6: Rinse the funnel with distilled water several times and use a wash bottle to flush the adherent particles into the volumetric flask.

Step 7: Add a small amount of water while washing the funnel.  The amount of distilled water used for this should not exceed 50 ml.

Step 8: Rinse the funnel with distilled water and rinse the solution to the funnel into a flask. 

Step 9: Rotate the volumetric flask until the oxalic acid dissolves. 

Step 10: Using a  wash bottle, fill the volumetric flask with sufficient distilled water just below the etched marks.

Step 11: Add the last ml of distilled water droplets to the volumetric flask until the reduced meniscus level touches the mark.

Step 12: Place a stopper in the opening of the flask and shake gently to even out the entire solution. 

Now, we will get a solution of M/10 oxalic acid.

Note - Oxalic acid is an organic compound found in many plants, including leafy greens, vegetables, fruits, cocoa, nuts, and seeds.

Laboratory Preparation of Oxalic Acid

In the laboratory, Oxalic Acid is easily produced by the oxidation of carbohydrates using any strong oxidizing agent. The reaction it follows is,

C₁₂H₂₂O₁₁ + 18[O] (HNO₃ and V₂O₅) → (COOH)₂ + H₂O

Commercial Preparation of Oxalic Acid

We produce Oxalic acid commercially by treating carbohydrates with nitric acid in the presence of a catalyst vanadium pentoxide, similar to that of laboratory preparation. Also, we can obtain oxalic acid by carbonylation of alcohol.

Properties of Oxalic Acid

Basic properties of the Oxalic acid is added in the table below,

Chemical Formula	C2H2O4
Molecular Weight	90.03 g/mol
Density	1.90 cm3
Appearence	White Crystals
Melting Point	190 °C (approx)
Solution	Colorless Solution

All the properties of Oxalic Acid are divided into two parts,

• Physical Properties of Oxalic Acid
• Chemical Properties of Oxalic Acid

Now let's learn about them in detail.

Physical Properties of Oxalic Acid

The physical properties of oxalic acid are,

• The molar mass of oxalic acid is 90 g/mol and for the hydrated oxalic acid molar mass is 126 g/mol. 
• Its Density is 1.90 g/cm³. 
• Its Melting points vary from 1890°C to 1910°C.
• It appears as a white crystal and smells odorless.
• It forms a colourless solution in water.
• Its heat capacity is 91.0 J·mol^-1·K^-1

Chemical Properties of Oxalic Acid

The chemical properties of oxalic acid are,

• For oxalic acid, the valence coefficient is 2. 
• It readily reacts with typical carboxylic acids to form acid chlorides and ester derivatives. 
• Oxalic acid is highly toxic and therefore harmful. Inhalation can cause serious damage to mucous membranes and the respiratory tract. Also, symptoms such as cough, and wheezing are one of the symptoms of this. It is also toxic if swallowed and can cause kidney failure.
• When oxalic acid reacts with Potassium Manganate(VII), get dissociates as:

2MnO₄^– + 5C₂H₂O₄ + 6H₃O⁺   →   2Mn²⁺ + 10CO₂ + 14H₂O

• The reaction of oxalic acid with concentrated sulphuric acid is given by,

 C₂H₂O₄ + H₂SO₄ (conc.)  →  CO + CO₂ + H₂O

Can We Eat Oxalic Acid?

Oxalic acid is a naturally occurring compound in many fruits, vegetables, nuts, and whole grains. While small amounts of oxalic acid are not harmful.

Chemical Reactions

Various chemical reactions of oxalic acid include,

Heat Treatment of Oxalic Acid

Heating Oxalic Acid at high temperatures of 150˚C results in the decarboxylation of oxalic acid and it results in the formation of Formic acid and carbon dioxide.

(COOH)₂ (heating) → HCOOH + CO₂

Reaction of Sulphuric Acid with Oxalic Acid

When oxalic acid is treated with conc. H₂SO₄ It produces carbon dioxide and carbon monoxide and water is removed.

(COOH)₂ + H₂SO₄(heating) →CO₂ + H₂O + CO

Oxalic Acid Reaction with KMnO₄

Oxalic acid oxidized to carbon dioxide and water in the presence of acidified Potassium Permanganate solution.

(COOH)₂ + [O] (KMnO₄ and H₂SO₄) →CO₂ + H₂O + CO

Oxalic Acid Uses

Various uses of the Oxalic Acid are added below:

• Oxalic acid encourages the dying process.
• As a strong acid, it is also useful as an extractor and reducing agent for lanthanide metals and as an analytical reagent.
• It can be used for polishing marble carvings and in bleach. 
• Oxalic acid is helpful in removing food and ink stains. 
• Also useful for developing movies and used in wastewater treatment to remove calcium deposits.

Oxalic Acid Health Hazards

Oxalic Acid has very serious health implications for the human body. Some of the health implications of Oxalic acid are,

• It is toxic in nature and ingestion of oxalic acid cause vomiting, diarrhea, severe gastrointestinal disorder, etc.
• On contact with the eyes, it causes irritation and can damage the eyes.
• Overconsumption of oxalic acid causes kidney damage. 
• Inhaling fumes of oxalic acid can cause headaches, dizziness, nausea, etc.

Also, Read

• Glutaric Acid Formula
• Fumaric Acid Formula
• Percarbonic Acid Formula