What Are the Main Uses and Health Effects of Oxalic Acid?
Oxalic acid is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. It is a key organic acid used in labs, industry, and even in cleaning and food chemistry studies.
What is Oxalic Acid in Chemistry?
Oxalic acid refers to a simple dicarboxylic acid with the chemical formula C2H2O4. This concept appears in chapters related to carboxylic acids, redox reactions, and acid-base behavior, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of oxalic acid is C2H2O4. It consists of two carboxyl (–COOH) groups joined together and is categorized under dicarboxylic acids. The IUPAC name is ethanedioic acid.
| Property | Oxalic Acid (Anhydrous) | Oxalic Acid (Dihydrate) |
|---|---|---|
| Molecular Formula | C2H2O4 | C2H2O4·2H2O |
| Molecular Mass (g/mol) | 90.03 | 126.07 |
| Appearance | Colourless, crystalline | Colourless crystals |
| Density (g/cm3) | 1.90 | 1.653 |
| Melting Point (°C) | 101 | 101 (decomposes) |
| Solubility | Water, alcohol, ether | Water, alcohol |
Preparation and Synthesis Methods
- Industrial oxalic acid is commonly made by oxidation of carbohydrates (like sugar, glucose, molasses) using nitric acid as an oxidizing agent.
- Another method uses catalytic oxidation of carbohydrates or heating sodium formate.
- In the lab, oxalic acid can be made by oxidizing sucrose or glucose with nitric acid or by reacting sodium oxalate with dilute sulfuric acid and crystallizing the solution.
- Always handle oxalic acid with care, as it is toxic in concentrated forms.
Physical Properties of Oxalic Acid
- Oxalic acid appears as colourless, odourless crystals in its pure form. It melts at 101°C (dihydrate) and sublimes when heated.
- It is highly soluble in water, and also dissolves in alcohol and ether. Its pKa1 is about 1.27, making it a stronger acid than acetic acid.
- The density differs between the anhydrous (1.90 g/cm3) and dihydrate (1.653 g/cm3) forms.
Chemical Properties and Reactions
- Oxalic acid is a strong organic acid and a powerful reducing agent. It reacts with bases to form oxalate salts, like calcium oxalate and sodium oxalate.
- In redox reactions, it reduces potassium permanganate (KMnO4) to Mn2+ ions while itself getting oxidized to carbon dioxide.
- It also decomposes upon strong heating to give CO and CO2, and reacts with metals to form chelates.
- Its acidic behavior is demonstrated clearly when titrated against a base in experiments.
Frequent Related Errors
- Confusing oxalic acid with acetic acid or other simple acids.
- Assuming all oxalic acid in plants is harmful (quantity and solubility matter).
- Ignoring its strong acid properties and redox behavior in school experiments.
- Mistaking oxalic acid’s crystal form as “salt” (it's the pure acid, not just a salt).
Uses of Oxalic Acid in Real Life
- Oxalic acid is widely used for cleaning, bleaching wood, removing rust, in textile processing, and in laboratories for titration experiments.
- It is also used by beekeepers (in safe controlled amounts) to control varroa mites in beehives.
- In household settings, it works as a stain remover for ink, rust, and some food stains.
- It is not added directly to foods but naturally exists in vegetables like spinach and rhubarb.
Relation with Other Chemistry Concepts
Oxalic acid is closely related to topics such as chemical reactions and redox reactions, helping students build a conceptual bridge between organic acids and analytical laboratory chemistry. It is also an example when studying organic acids and chelating agents.
Step-by-Step Reaction Example
- Start with the redox reaction between oxalic acid and potassium permanganate in acidic medium.
2 KMnO4 + 5 H2C2O4 + 6 H2SO4 → 2 MnSO4 + 10 CO2 + 8 H2O + K2SO4 - Explain each step.
Here, oxalic acid (reductant) donates electrons, getting oxidized to CO2, while Mn in KMnO4 is reduced from +7 to +2.
Lab or Experimental Tips
Remember oxalic acid by the rule that it turns potassium permanganate from purple to colourless in redox titrations. Vedantu educators often use the “KMnO4 disappears” trick to help students track oxidation visually.
Try This Yourself
- Write the IUPAC name of oxalic acid.
- Explain what happens if you add calcium chloride to an oxalic acid solution.
- List two vegetables high in oxalic acid content.
- Draw the structure of the oxalate ion (C2O42−).
Final Wrap-Up
We explored oxalic acid—its structure, properties, reactions, and real-life importance. For more in-depth explanations and easy-to-follow chemistry revision, check out live classes and study notes on Vedantu for other key topics like tartaric acid.
FAQs on Oxalic Acid – Formula, Structure, Properties & Applications
1. What is the formula of oxalic acid?
The formula of oxalic acid is C2H2O4. It consists of two carboxylic acid groups joined together. Oxalic acid is often written as HOOC–COOH to show its structure clearly.
2. What are the main uses of oxalic acid?
Oxalic acid has several practical and laboratory uses:
• Cleaning agent for removing rust and stains
• Bleaching wood and textiles
• Laboratory reagent in titrations and preparation reactions
• Used by beekeepers to help control varroa mites
• Involved in leather and metal treatment industries
3. Is oxalic acid safe to handle and consume?
Oxalic acid should be handled with care, as large amounts can be toxic.
• In small amounts found naturally in food, it is generally safe for most people.
• Ingestion of high levels can cause harm to the kidneys by forming calcium oxalate crystals.
• Always use gloves and safety equipment when handling concentrated oxalic acid.
4. Which foods contain a high amount of oxalic acid?
Several foods naturally contain oxalic acid, including:
• Spinach
• Rhubarb
• Beet greens
• Cocoa and chocolate
• Nuts like almonds and cashews
Eating a balanced diet helps minimize any risk from oxalic acid in foods.
5. Why is oxalic acid called a dicarboxylic acid?
Oxalic acid is categorized as a dicarboxylic acid because:
• It contains two carboxylic (COOH) groups in its molecules.
• The presence of two COOH groups allows it to participate in specific chemical reactions and form salts called oxalates.
6. What type of chemical reactions does oxalic acid participate in?
Oxalic acid is involved in both acid-base and redox reactions:
• Acts as a weak acid in neutralization reactions with bases
• Functions as a reducing agent in redox reactions, especially with potassium permanganate (KMnO4)
• Forms salts like sodium oxalate when reacted with bases
7. How is oxalic acid manufactured industrially?
Oxalic acid is produced by methods such as:
• Oxidation of carbohydrates like sugar using nitric acid
• Heating sodium formate to produce sodium oxalate, followed by acidification
• Industrial synthesis ensures pure and safe products for various uses
8. What happens if oxalic acid is consumed in excessive amounts?
High intake of oxalic acid can lead to serious health issues:
• May cause kidney stones by forming insoluble calcium oxalate crystals
• Can result in abdominal discomfort, nausea, or serious poisoning in large doses
• Individuals with kidney problems or certain metabolic conditions should avoid excessive intake
9. What is the role of oxalic acid in plants?
In plants, oxalic acid:
• Acts as a natural defense against herbivores and pathogens
• Regulates calcium by forming calcium oxalate crystals
• May serve as a way for plants to store excess minerals safely
10. Why is oxalic acid used in cleaning and wood bleaching?
Oxalic acid is effective in cleaning and bleaching because:
• It acts as a strong reducing agent, removing rust and mineral stains
• It helps restore the natural color of wood by breaking down discolorations
• Its acidic nature dissolves iron and calcium deposits on surfaces
11. How does oxalic acid act as a reducing agent in redox reactions?
Oxalic acid works as a reducing agent by:
• Donating electrons to other substances (such as potassium permanganate)
• Undergoing oxidation itself to form carbon dioxide and water
• Allowing color changes in titrations, useful for laboratory analysis
12. What is the IUPAC name and structure of oxalic acid?
The IUPAC name of oxalic acid is ethanedioic acid.
• Its structure is depicted as HOOC–COOH
• It is the simplest dicarboxylic acid, with two adjacent carboxyl groups attached to a two-carbon chain
