Nitric acid is one of the most important mineral acids studied in basic and advanced chemistry. The nitric acid formula is HNO₃, which shows that it contains one hydrogen (H), one nitrogen (N), and three oxygen (O) atoms. When we talk about the nitric acid formula with charge, it is usually written as H⁺ and NO₃⁻ in aqueous solution, because nitric acid is a strong acid and completely ionizes in water. The nitric acid formula structure shows a trigonal planar arrangement around the nitrogen atom, with resonance between the oxygen atoms, which makes the nitrate ion stable.
The nitric acid molar mass is about 63.01 g/mol, and the nitric acid formula mass is calculated by adding the atomic masses of hydrogen, nitrogen, and oxygen atoms. Students often compare it with other acids like acetic acid formula (CH₃COOH) to understand differences between organic and inorganic acids.
It is also important not to confuse it with the nitric oxide formula, which is NO, a completely different compound with different properties. There are many nitric acid uses, including fertilizer production, explosives manufacturing, laboratory reagent, and metal cleaning. Because of its strong oxidizing nature, it must be handled carefully in chemistry labs and industries, although sometimes students forget how reactive it can be.
What is Nitric Acid?
Nitric acid is a highly corrosive mineral acid with the chemical formula HNO₃. It’s a colorless to pale yellow liquid with a sharp, suffocating odor. In school labs, you’ll encounter it as a reagent for various experiments, especially in metal reactions and qualitative analysis.
Why it matters in academics:
- Appears in CBSE Board, ICSE, and state board exams
- Essential for understanding acid-base chemistry
- Key compound in industrial chemistry chapters
- Frequently asked in JEE, NEET, and competitive exams
Chemical Formula of Nitric Acid
The chemical formula of nitric acid is HNO₃.
This formula tells us that one molecule of nitric acid contains:
- 1 Hydrogen (H) atom
- 1 Nitrogen (N) atom
- 3 Oxygen (O) atoms
Molecular formula of nitric acid: HNO₃
Molecular weight: 63.01 g/mol
Structural representation: H-O-NO₂
Nitric Acid Formula Formula Table
Here’s everything you need to know about nitric acid formulas in one comprehensive table:
| Property |
Details |
| Chemical Formula |
HNO₃ |
| Molecular Formula |
HNO₃ |
| Condensed Formula |
HNO₃ |
| Empirical Formula |
HNO₃ |
| Structural Formula |
H-O-NO₂ |
| Molecular Weight |
63.01 g/mol |
| IUPAC Name |
Nitric(V) acid |
| Common Name |
Aqua fortis, Spirit of niter |
| Conjugate Base |
Nitrate ion (NO₃⁻) |
| Acid Dissociation (Strong Acid) |
HNO₃ → H⁺ + NO₃⁻ |
| Oxidation State of Nitrogen |
+5 |
| Hybridization of Nitrogen |
sp² |
| Molecular Geometry |
Trigonal planar (around N) |
| Bond Angle (O-N-O) |
~120° |
| Density |
1.51 g/cm³ (concentrated) |
| Boiling Point |
83°C (181°F) |
| pH Range |
<1 (highly acidic) |
Molecular Structure Explained
Understanding the structure helps you remember the formula forever.
Lewis Structure:
- Nitrogen is the central atom
- One oxygen is bonded to hydrogen (O-H)
- Two other oxygens are double-bonded to nitrogen
- One resonance structure exists
Key structural features:
- The nitrogen atom has a +5 oxidation state
- sp² hybridization makes it planar
- The H atom is attached to oxygen, not nitrogen
- Resonance stabilizes the molecule
Simple diagram representation:
Types and Concentrations
Nitric acid comes in different concentrations for various purposes.
| Type |
Concentration |
Uses |
| Dilute Nitric Acid |
~10-20% HNO₃ |
School lab experiments, weak acid reactions |
| Concentrated Nitric Acid |
~68-70% HNO₃ |
Industrial use, strong oxidizing reactions |
| Fuming Nitric Acid |
>90% HNO₃ + NO₂ |
Rocket fuel, explosives manufacturing |
| White Fuming Nitric Acid (WFNA) |
98% HNO₃ |
Specialized industrial applications |
| Red Fuming Nitric Acid (RFNA) |
>84% with dissolved NO₂ |
Gives reddish-brown color |
For exams, remember:
Concentrated nitric acid is typically 68% HNO₃ and acts as a strong oxidizing agent.
Preparation Methods
1. Laboratory Method (Ostwald Process):
4NH₃ + 5O₂ → 4NO + 6H₂O
2NO + O₂ → 2NO₂
3NO₂ + H₂O → 2HNO₃ + NO
2. Contact Process (from sodium nitrate):
NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃
This is the most common school lab preparation method you’ll encounter.
3. Industrial Preparation: Uses the Ostwald process on a large scale with platinum-rhodium catalyst.
Important Chemical Reactions
1. Reaction with metals (except noble metals):
3Cu + 8HNO₃ (dilute) → 3Cu(NO₃)₂ + 2NO + 4H₂O
Cu + 4HNO₃ (conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O
2. With non-metals:
C + 4HNO₃ → CO₂ + 4NO₂ + 2H₂O
S + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O
3. Aqua regia (royal water):
HNO₃ + 3HCl → NOCl + Cl₂ + 2H₂O
This mixture can dissolve gold and platinum.
4. Brown ring test (qualitative analysis for nitrates):
[Fe(H₂O)₆]²⁺ + NO → [Fe(H₂O)₅(NO)]²⁺ + H₂O
Forms a brown-colored complex ring.
Common Mistakes Students Make
1. Writing HNO₂ instead of HNO₃, HNO₂ is nitrous acid, not nitric acid
2. Confusing molecular mass (63) with atomic numbers, Molecular mass = 1 + 14 + 48 = 63 g/mol
3. Thinking nitrogen has -3 oxidation state, In HNO₃, nitrogen has +5 oxidation state
4. Writing H₃NO₃ or NH₃O, Always write HNO₃ in correct order
5. Assuming all acids have H at the beginning, In structural formula, H is bonded to oxygen, not nitrogen
6. Forgetting it’s a strong acid, HNO₃ completely dissociates in water
Memory Tricks
Trick 1: “H-NO-Three”
Just remember: Hydrogen-Nitrogen-Oxygen (3 times)
Trick 2: Phone Number Method
HNO₃ = “1-1-3” (one H, one N, three O)
Trick 3: Valency Match
H is +1, NO₃ group is -1, so HNO₃ is neutral
Trick 4: Formula Pyramid
Trick 5: The “Strong Three”
Remember the three common strong acids: HCl, H₂SO₄, HNO₃
Conclusion
Understanding the nitric acid formula (HNO₃) goes beyond just memorizing three letters and a number. It’s about recognizing one of chemistry’s most versatile compounds—a strong acid, powerful oxidizer, and industrial workhorse that appears repeatedly in your academic journey. From board exams to competitive tests, this formula will follow you through chemistry chapters on acids, redox reactions, and qualitative analysis.
Remember: one hydrogen, one nitrogen, three oxygens simple as that. Practice writing it, understand its structure, and you’ll never confuse it with any other acid formula again. Chemistry becomes easier when you grasp these fundamentals clearly. Keep this guide handy, and you’re all set to ace those chemistry questions!
FAQs about Nitric Acid Formula
Q1: What is the chemical formula of nitric acid?
The chemical formula of nitric acid is HNO₃, consisting of one hydrogen atom, one nitrogen atom, and three oxygen atoms bonded together. It’s a strong monoprotic acid widely used in laboratories and industries.
Q2: What is the molecular formula of nitric acid?
The molecular formula of nitric acid is HNO₃. This is the same as its chemical formula since it represents the actual number of atoms in one molecule with a molecular weight of 63.01 g/mol.
Q3: Is nitric acid a strong acid or weak acid?
Nitric acid is a strong acid because it completely dissociates in aqueous solution to form H⁺ and NO₃⁻ ions. It has a very low pH (less than 1) and reacts vigorously with bases and metals.
Q4: What is the oxidation state of nitrogen in HNO₃?
The oxidation state of nitrogen in HNO₃ is +5. This is calculated considering hydrogen as +1, oxygen as -2, and solving: +1 + N + 3(-2) = 0, giving N = +5.
Q5: Why does concentrated nitric acid turn yellow?
Concentrated nitric acid turns pale yellow due to photochemical decomposition. Exposure to light causes partial breakdown into nitrogen dioxide (NO₂), which dissolves in the acid, giving it a yellowish tint.
Q6: What happens when nitric acid reacts with copper?
Dilute nitric acid reacts with copper to produce copper nitrate, nitric oxide gas, and water. Concentrated nitric acid produces copper nitrate, nitrogen dioxide (brown fumes), and water. Both are redox reactions showing nitric acid’s oxidizing nature.
Q7: Can nitric acid dissolve gold?
Pure nitric acid cannot dissolve gold. However, a mixture of nitric acid and hydrochloric acid (3:1 ratio), called aqua regia, can dissolve gold and platinum by forming soluble chloride complexes.
Q8: What is the difference between HNO₃ and HNO₂?
HNO₃ is nitric acid (strong acid, N in +5 state), while HNO₂ is nitrous acid (weak acid, N in +3 state). Nitric acid is stable and widely used; nitrous acid is unstable and exists mainly in solution.
