Basic Chemical Formulas
| Formula Type | Formula | Explanation |
|---|---|---|
| Chemical Formula | HNO₃ | Basic chemical formula showing one hydrogen, one nitrogen, and three oxygen atoms |
| Molecular Formula | HNO₃ | Same as chemical formula – represents the actual number of atoms in one molecule |
| Empirical Formula | HNO₃ | Simplest whole number ratio of atoms (same as molecular formula for nitric acid) |
| Condensed Formula | HONO₂ | Alternative representation showing the structural arrangement |
Structural Representations
| Type | Formula/Structure | Description |
|---|---|---|
| Structural Formula | H-O-NO₂ | Shows how atoms are bonded together |
| Lewis Structure | H-O-N(=O)-O | Complete electron dot structure with bonds |
| IUPAC Name | Nitric acid | Official chemical name |
| Common Names | Aqua fortis, Spirit of niter | Historical and common names |
Concentration-Based Formulas
| Concentration Type | Formula/Composition | Details |
|---|---|---|
| Concentrated Nitric Acid | 68-70% HNO₃ | Commercial concentrated form |
| Dilute Nitric Acid | <20% HNO₃ in H₂O | Commonly used in laboratories |
| Fuming Nitric Acid | >90% HNO₃ + NO₂ | Red/yellow fuming, highly concentrated |
| Molar Concentration | M = n/V | Where M = molarity, n = moles, V = volume in liters |
Production Formulas (Ostwald Process)
| Step | Chemical Equation | Process Description |
|---|---|---|
| Step 1 | 4NH₃ + 5O₂ → 4NO + 6H₂O | Ammonia oxidation (catalyst: Pt) |
| Step 2 | 2NO + O₂ → 2NO₂ | Nitrogen monoxide oxidation |
| Step 3 | 3NO₂ + H₂O → 2HNO₃ + NO | Nitrogen dioxide absorption in water |
| Overall | NH₃ + 2O₂ → HNO₃ + H₂O | Net reaction for nitric acid production |
Dissociation and Ionization
| Process | Chemical Equation | Explanation |
|---|---|---|
| Complete Dissociation | HNO₃ → H⁺ + NO₃⁻ | Strong acid – complete ionization |
| In Water | HNO₃ + H₂O → H₃O⁺ + NO₃⁻ | Proton transfer to water |
| Ka Expression | Ka = [H⁺][NO₃⁻]/[HNO₃] | Very large value (strong acid) |
Important Reactions with Metals
| Reaction Type | General Formula | Example |
|---|---|---|
| With Active Metals | M + HNO₃ → M(NO₃)ₙ + NOₓ + H₂O | Zn + 4HNO₃ → Zn(NO₃)₂ + 2NO₂ + 2H₂O |
| With Copper | Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O | Brown gas (NO₂) evolution |
| With Silver | Ag + 2HNO₃ → AgNO₃ + NO₂ + H₂O | Dilute acid produces NO instead |
Reactions with Non-Metals
| Reactant | Chemical Equation | Products |
|---|---|---|
| Carbon | C + 4HNO₃ → CO₂ + 4NO₂ + 2H₂O | Carbon dioxide and nitrogen dioxide |
| Sulfur | S + 6HNO₃ → H₂SO₄ + 6NO₂ + 2H₂O | Sulfuric acid formation |
| Phosphorus | P + 5HNO₃ → H₃PO₄ + 5NO₂ + H₂O | Phosphoric acid production |
Physical Property Formulas
| Property | Formula/Value | Units |
|---|---|---|
| Molecular Weight | 63.01 g/mol | Grams per mole |
| Density (pure) | 1.51 g/cm³ | At 25°C |
| Boiling Point | 83°C (181°F) | At 1 atm pressure |
| Melting Point | -42°C (-44°F) | Freezing point |
Titration and Analytical Formulas
| Calculation | Formula | Application |
|---|---|---|
| Molarity | M = (n × 1000)/V | n = moles, V = volume in mL |
| Normality | N = M × n | n = number of H⁺ ions (1 for HNO₃) |
| pH Calculation | pH = -log[H⁺] | For dilute solutions |
| Neutralization | M₁V₁ = M₂V₂ | Acid-base titrations |
Environmental and Safety Formulas
| Process | Chemical Equation | Environmental Impact |
|---|---|---|
| Acid Rain Formation | 4NO₂ + 2H₂O + O₂ → 4HNO₃ | Major contributor to acid precipitation |
| Ozone Depletion | HNO₃ + hν → OH + NO₂ | Photochemical decomposition |
Study Points for Students
Essential Formulas to Memorize:
- Basic Formula: HNO₃
- Ostwald Process: 4NH₃ + 5O₂ → 4NO + 6H₂O
- Complete Ionization: HNO₃ → H⁺ + NO₃⁻
- With Copper: Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O
Important Properties:
- Strong monoprotic acid (releases one H⁺ ion)
- Powerful oxidizing agent (especially when concentrated)
- Molecular weight: 63.01 g/mol
- Completely miscible with water
Laboratory Safety:
- Always add acid to water, never water to acid
- Use proper ventilation due to toxic NO₂ fumes
- Wear appropriate protective equipment
- Store in dark, cool places to prevent decomposition
Frequently Asked Questions (FAQs)
Q. What is the chemical formula of nitric acid?
The chemical formula of nitric acid is HNO₃. It consists of one hydrogen (H) atom, one nitrogen (N) atom, and three oxygen (O) atoms. This formula represents both the molecular and empirical formula of nitric acid.
Q. Is nitric acid a strong acid or weak acid?
Nitric acid is a strong acid. It completely dissociates in water according to the equation: HNO₃ → H⁺ + NO₃⁻. This complete ionization makes it one of the seven strong acids commonly taught in chemistry, along with HCl, H₂SO₄, HBr, HI, HClO₄, and HClO₃.
Q. What is the difference between concentrated and dilute nitric acid?
- Concentrated nitric acid contains 68-70% HNO₃ by weight in water
- Dilute nitric acid contains less than 20% HNO₃ in water
- Fuming nitric acid contains over 90% HNO₃ with dissolved NO₂ gas
The concentration affects reactivity significantly. Concentrated acid acts as a strong oxidizing agent, while dilute acid behaves more like a typical acid.
Q. How is nitric acid prepared in industry?
Nitric acid is prepared industrially through the Ostwald Process in three steps:
- 4NH₃ + 5O₂ → 4NO + 6H₂O (ammonia oxidation)
- 2NO + O₂ → 2NO₂ (further oxidation)
- 3NO₂ + H₂O → 2HNO₃ + NO (absorption in water)
This process uses a platinum catalyst and operates at high temperatures (800-900°C).
Q. What is the molecular weight (molar mass) of nitric acid?
The molecular weight of nitric acid (HNO₃) is 63.01 g/mol, calculated as:
- H = 1.01 g/mol
- N = 14.01 g/mol
- O₃ = 3 × 16.00 = 48.00 g/mol
- Total = 63.01 g/mol
Q. Why does nitric acid react differently with different metals?
Nitric acid acts as both an acid and an oxidizing agent. Its reactions depend on:
- Concentration: Concentrated vs dilute acid produce different gases (NO₂ vs NO)
- Metal reactivity: Active metals like zinc produce different products than less active metals like copper
- Temperature: Higher temperatures increase oxidizing power
Example with copper: Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O
Q. What is the pH value of nitric acid?
The pH depends on concentration:
- 1 M HNO₃ solution: pH ≈ 0
- 0.1 M HNO₃ solution: pH ≈ 1
- 0.01 M HNO₃ solution: pH ≈ 2
Formula: pH = -log[H⁺]. Since HNO₃ completely dissociates, [H⁺] equals the molarity of the acid.
Q. What happens when nitric acid reacts with copper?
This is a classic laboratory reaction producing brown nitrogen dioxide gas:
3Cu + 8HNO₃(dilute) → 3Cu(NO₃)₂ + 2NO + 4H₂O (colorless NO gas)
Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O (brown NO₂ gas)
The brown fumes are toxic nitrogen dioxide. This reaction demonstrates nitric acid’s oxidizing properties.
Q. What is the difference between HNO₃ and HNO₂?
- HNO₃ (Nitric Acid): Strong acid, stable, nitrogen in +5 oxidation state
- HNO₂ (Nitrous Acid): Weak acid, unstable, nitrogen in +3 oxidation state
HNO₃ is commonly used and commercially available, while HNO₂ exists mainly in solution and decomposes easily.
Q. What is aqua regia and how is it related to nitric acid?
Aqua regia is a mixture of concentrated nitric acid and hydrochloric acid in a 1:3 ratio: HNO₃ + 3HCl → NOCl + Cl₂ + 2H₂O
This “royal water” can dissolve noble metals like gold and platinum, which neither acid can do alone.
The reaction with gold is: Au + HNO₃ + 4HCl → HAuCl₄ + NO + 2H₂O
Q. Why does nitric acid turn yellow on storage?
Nitric acid decomposes when exposed to light according to: 4HNO₃ → 4NO₂ + 2H₂O + O₂
The yellow/brown color comes from dissolved nitrogen dioxide (NO₂) gas. This is why nitric acid should be stored in:
- Dark brown bottles (to prevent light exposure)
- Cool places (to reduce decomposition)
- Tightly sealed containers
Q. What is the valency and oxidation state of nitrogen in HNO₃?
Answer:
- Oxidation state of nitrogen: +5 (highest oxidation state for nitrogen)
- Valency: 5 (in the context of combining capacity)
This high oxidation state makes nitric acid a powerful oxidizing agent, as nitrogen can easily accept electrons to reach lower oxidation states.
Q. Can nitric acid dissolve gold?
Pure nitric acid cannot dissolve gold because gold is too noble. However, aqua regia (a mixture of HNO₃ and HCl in 1:3 ratio) can dissolve gold through a complex reaction that generates chlorine and nitrosyl chloride, which then react with gold to form chloroauric acid.
Q. What are the main uses of nitric acid?
Major applications include:
- Fertilizer production (ammonium nitrate, calcium nitrate)
- Explosives manufacturing (TNT, nitroglycerin)
- Chemical synthesis (adipic acid for nylon)
- Metal etching and cleaning
- Pharmaceuticals production
- Dye manufacturing
Q. Is nitric acid dangerous? What safety precautions are needed?
Yes, nitric acid is highly corrosive and dangerous. Safety measures include:
- Wear protective equipment (gloves, goggles, lab coat)
- Work in well-ventilated areas (toxic NO₂ fumes)
- Always add acid to water, never water to acid (exothermic reaction)
- Store in dark, cool places away from organic materials
- Have neutralizing agents (sodium bicarbonate) nearby
- Know emergency procedures for spills and exposure
Q. What is the normality of 1M nitric acid?
For nitric acid, Normality (N) = Molarity (M) × basicity
Since HNO₃ is monoprotic (releases 1 H⁺ ion), basicity = 1
Therefore, 1M HNO₃ = 1N HNO₃
Q. Does nitric acid react with glass?
Dilute and moderately concentrated nitric acid do not significantly react with glass, making glass containers suitable for storage. However, hot concentrated nitric acid or hydrofluoric acid (HF) can react with glass. This is why nitric acid is commonly stored in glass bottles in laboratories.
Q. What is the boiling point of nitric acid?
Pure nitric acid has a boiling point of 83°C (181°F) at atmospheric pressure. However, when heated, it decomposes before boiling, releasing toxic nitrogen dioxide fumes. The azeotropic mixture (68% HNO₃) boils at approximately 120.5°C.
Q. How do you calculate the molarity of nitric acid from density?
Use the formula: Molarity (M) = (Density × Percentage purity × 10) / Molecular weight
For example, concentrated HNO₃ (68%, density = 1.41 g/mL): M = (1.41 × 68 × 10) / 63.01 = 15.2 M
Q. Why doesn’t nitric acid release hydrogen gas with metals?
Unlike other acids, nitric acid is a strong oxidizing agent. It oxidizes the hydrogen gas that would normally form:
H₂ + 2HNO₃ → 2H₂O + 2NO₂
Instead, nitric acid releases nitrogen oxides (NO, NO₂, N₂O) depending on concentration and reaction conditions. This makes HNO₃ unique among common acids.