What is Boric Acid? (H3BO3) Formula, Structure, Properties & Key Uses
Boric acid is essential in chemistry and helps students understand various practical and theoretical applications related to this topic.
What is Boric Acid in Chemistry?
A boric acid refers to a weak inorganic acid with the formula H3BO3. This concept appears in chapters related to buffer solutions, antiseptics, and inorganic acid chemistry, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
The molecular formula of boric acid is H3BO3. It consists of three hydrogen atoms, one boron atom, and three oxygen atoms, and is categorized under weak inorganic acids. Its structure features a trigonal planar geometry with boron at the center coordinated to three hydroxyl groups. Boric acid is also known as orthoboric acid or trihydrooxidoboron.
Preparation and Synthesis Methods
Boric acid can be prepared using several methods, both industrially and in the laboratory:
-
Reaction of borax with mineral acids:
Na2B4O7·10H2O + 2HCl → 4B(OH)3 + 2NaCl + 5H2O -
Hydrolysis of boron trihalides:
BX3 + 3H2O → B(OH)3 + 3HX (where X = Cl, Br, I) -
Hydrolysis of diborane:
B2H6 + 6H2O → 2B(OH)3 + 6H2
Laboratory-scale preparation typically starts with borax, which is a safe and convenient source for students.
Physical Properties of Boric Acid
Appearance: Colorless or white crystalline solid
Solubility: Soluble in water (higher at higher temperatures)
Molar mass: 61.83 g/mol
Melting point: 170.9°C (decomposes)
Boiling point: Not applicable (decomposes on heating)
Density: About 1.435 g/cm³
Odor: Odorless
pKa (acidity): Around 9.24 (acts as a weak acid)
Chemical Properties and Reactions
Boric acid shows these typical reactions:
- On heating at 170°C: H3BO3 → HBO2 + H2O (forms metaboric acid)
- On heating above 330°C: 2H2B4O7 → 2B2O3 + H2O (forms boron trioxide)
- Reacts with alcohol (e.g., methanol): Forms borate esters
- Reacts with strong bases: Converts to various borate salts
- Weak acid: Does not directly donate protons; instead, it acts as a Lewis acid by accepting hydroxide ions
Frequent Related Errors
- Confusing boric acid with neutral molecules or different acids.
- Ignoring structural polarity during explanation.
- Assuming boric acid is a strong acid—it's actually weak and acts as a Lewis acid.
- Mixing up boric acid with borax or borates in reactions.
Uses of Boric Acid in Real Life
Boric acid is widely used in medical, laboratory, and industrial settings. Real-life applications include:
- Eye washes and mild antiseptics (when used properly and in controlled amounts)
- Laboratory buffer solutions and titration experiments (see Buffer Solutions)
- Insecticide and pest control (e.g., for ants and cockroaches)
- Flame retardant additives in plastics and glass production
- Used in nuclear power plants as a neutron absorber
- Glass and ceramics manufacturing
- Wood preservation and lubricants
Learn more on Vedantu about its varied uses and handling in chemistry labs.
Relevance in Competitive Exams
Students preparing for NEET, JEE, and Olympiads should be familiar with boric acid, as it often features in reaction-based questions, structure identification, and comparisons with other acids (see Properties of Acids and Bases), as well as MCQs about its industrial and medical uses.
Relation with Other Chemistry Concepts
Boric acid is closely related to topics such as Boron and Its Compounds and Borax Formula, helping students build a conceptual bridge between acids, salts, and buffer systems in inorganic chemistry. Understanding its Lewis acid character is also helpful for grasping other acid-base concepts.
Step-by-Step Reaction Example
- Start with the reaction setup.
Take borax (Na2B4O7·10H2O) and dilute hydrochloric acid (HCl). - Write the balanced equation.
Na2B4O7·10H2O + 2HCl → 4B(OH)3 + 2NaCl + 5H2O - Explain each intermediate or by-product.
Crystalline boric acid forms as the solution cools; sodium chloride and water are by-products. - State conditions.
Reaction should be performed with constant stirring and gentle heating, followed by cooling to crystallize boric acid.
Lab or Experimental Tips
Remember boric acid by the rule of “weak but effective.” Vedantu educators often use lab demonstrations showing its slow bubbling with bases or its poor reactivity with indicators, illustrating its distinction from strong acids.
Try This Yourself
- Write the IUPAC name of boric acid.
- Is boric acid acidic, neutral, or basic when dissolved in water?
- Give two real-life examples of boric acid applications.
Final Wrap-Up
We explored boric acid—its structure, properties, reactions, and real-life importance. For more in-depth explanations and exam-prep tips, explore live classes and chemistry notes on Vedantu.
Borax Formula
Properties of Acids and Bases
Buffer Solutions
Boron and Its Compounds
FAQs on Boric Acid: Definition, Formula, Structure, Preparation & Uses
1. What is boric acid used for in chemistry?
Boric acid, or H3BO3, finds versatile applications in chemistry. It's a crucial reagent in laboratory experiments, acting as a weak acid and a buffer in various solutions and titrations. Additionally, its antiseptic properties make it useful in certain applications.
2. Is boric acid safe for human use?
Boric acid's safety depends entirely on the dosage and application. In low concentrations, it's generally safe for external use as an antiseptic (e.g., in eye washes). However, ingesting or using large amounts can be toxic. Always follow directions carefully and consult a healthcare professional before use.
3. Why is boric acid banned in some countries?
Bans or restrictions on boric acid often stem from concerns about its toxicity, particularly the potential for accidental ingestion, especially by children. The risks associated with its use, especially in food products, lead to regulatory actions to protect public health.
4. What is the molar mass of boric acid?
The molar mass of boric acid (H3BO3) is approximately 61.83 g/mol.
5. How is boric acid prepared in the laboratory?
Laboratory preparation often involves reacting borax (sodium borate) with a mineral acid such as hydrochloric acid (HCl) or sulfuric acid (H2SO4). Cooling the solution allows the formation of boric acid crystals.
6. Why is boric acid considered a weak acid?
Unlike typical Brønsted-Lowry acids, boric acid doesn't directly donate protons (H+). Instead, it acts as a Lewis acid, accepting a hydroxide ion (OH-) from water. This makes it a relatively weak acid.
7. Does boric acid neutralize strong bases?
Yes, boric acid can neutralize strong bases, but it reacts slowly and weakly compared to stronger acids. It’s more commonly used as a buffer component to maintain a stable pH.
8. Can boric acid replace stronger acids in laboratory reactions?
No, its weak acidity limits its use in reactions requiring a strong acid. Stronger acids are necessary for reactions where a higher concentration of protons is needed.
9. What’s the difference between boric acid and borates?
Boric acid (H3BO3) is the parent compound. Borates are its salts formed when boric acid reacts with a base. A common example is sodium borate (borax).
10. How does boric acid inhibit bacteria and fungi?
Boric acid's antimicrobial action is complex. It disrupts the cell wall and membrane functions of microorganisms, which prevents cell growth and ultimately leads to the death of bacteria and fungi.
11. What is the chemical structure of boric acid?
Boric acid has a planar structure with a central boron atom surrounded by three hydroxyl groups (-OH). The boron atom is bonded to three oxygen atoms in a trigonal planar geometry, and each oxygen atom is bonded to a hydrogen atom.
12. What are the physical properties of boric acid?
Boric acid is a colorless, crystalline solid at room temperature. Key properties include: a molar mass of approximately 61.83 g/mol; a melting point of 171 °C; and good solubility in water. It's often found in powder form.
