Molar Mass of Benzene (C₆H₆)
Learn how chemists calculate the molar mass of Benzene (C₆H₆), with a clear formula breakdown, worked steps, and study notes.
Quick answer
The molar mass of Benzene (C₆H₆) is
78.114g/mol
One mole of Benzene therefore has a mass of 78.114 grams—the value you use for stoichiometry and laboratory preparation.
Reviewed for educational accuracy · Accuracy policy
- CAS Registry Number
- 71-43-2
- PubChem CID
- 241
- SMILES
- c1ccccc1
Step-by-step calculation
Let's find the molar mass of Benzene (C₆H₆) together—step by step, as if you are seeing the formula for the first time.
Step 1 — Look at the chemical formula
The formula is C₆H₆. Each letter stands for an element. The little number after a letter (the subscript) tells you how many atoms of that element are in one molecule or formula unit.
- 6 Carbon atoms (C)
- 6 Hydrogen atoms (H)
Step 2 — Look up each atomic mass
Atomic mass comes from the periodic table. It is the average mass of one mole of atoms of that element, in grams per mole (g/mol). Think of it as the "price tag" for one mole of that element.
- Carbon (C) = 12.011 g/mol
- Hydrogen (H) = 1.008 g/mol
Step 3 — Multiply atoms × atomic mass
Why multiply? If one oxygen atom "costs" about 16 g/mol, then two oxygen atoms cost twice as much. Each element's contribution is: number of atoms × atomic mass.
- 6 × 12.011 = 72.066 g/mol (Carbon)
- 6 × 1.008 = 6.048 g/mol (Hydrogen)
Step 4 — Add the contributions
Why add? The molar mass of the whole compound is simply the total mass of every atom in the formula. Add each element's contribution:
72.066 + 6.048 = 78.114 g/mol
Step 5 — Final answer
Molar mass of Benzene = 78.114 g/mol
That means one mole of Benzene (C₆H₆) has a mass of about 78.11 grams.
Quick summary
Read the formula → count atoms → look up atomic masses → multiply → add → report g/mol. For C₆H₆, the total is 78.114 g/mol.
Common beginner mistakes
- Drawing alternating single/double bonds as fixed Kekulé structure instead of delocalized.
- Predicting addition reactions like alkenes — benzene prefers substitution.
- Confusing benzene with cyclohexane (C₆H₁₂, M = 84.16, saturated, not aromatic).
Memory trick
Use circle in ring to indicate delocalization in exam diagrams.
Mini practice
Without looking above, list the atoms in C₆H₆ and write one multiplication line for the heaviest element. Then check your work against Step 3.
Real-world example
If a recipe asks for 0.100 mol of Benzene, mass needed = 0.100 × 78.114 = 7.811 g. That is how chemists turn a mole amount into a weighable sample.
Atomic contribution table
Each row shows how much mass one element contributes to the total for C₆H₆.
| Element | Atoms | Atomic mass | Contribution | Mass % |
|---|---|---|---|---|
| C | 6 | 12.011 | 72.066 g/mol | 92.3% |
| H | 6 | 1.008 | 6.048 g/mol | 7.7% |
| Total molar mass | 78.114 g/mol | 100% | ||
Mass contribution chart
Count every atom in this formula, multiply by atomic mass, then add. That total is the molar mass used in lab weighing.
Download study sheets
Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Benzene (C₆H₆).
Practice this calculation
Without looking above, write the atom count for C₆H₆, then compute the molar mass. Check your answer against 78.114 g/mol.
Next challenge: how many grams are in 0.250 mol of Benzene? Multiply 0.250 × 78.114 to get 19.529 g.
Physical and chemical properties
Physical properties
| Appearance | Colorless liquid |
| Color | Colorless |
| Odor | Sweet, aromatic (not to be confused with safety — toxic) |
| State (STP) | Liquid (melting point 5.5 °C, boiling point 80.1 °C) |
| Density | 0.8765 g/cm³ at 20 °C |
| Melting point | 5.55 °C |
| Boiling point | 80.1 °C |
| Solubility | 1.79 g/L water at 25 °C (slightly soluble); miscible with organic solvents |
| Crystal structure | Orthorhombic (solid below 5.5 °C) |
Chemical properties
| Classification | Aromatic hydrocarbon |
| Family | Arenes / aromatic hydrocarbons |
| Polarity | Non-polar |
| Geometry | Planar hexagonal ring |
| Bond angle | 120° (sp² trigonal planar at each carbon) |
| Oxidation states | C: average 0 in ring (formally mixed) |
Applications
Industrial uses
- Styrene production (for polystyrene and ABS plastics)
- Cumene process for phenol and acetone
- Cyclohexane production (nylon 6,6 precursor via adipic acid)
- Aniline production (dyes, polyurethane)
Laboratory uses
- Solvent for organic reactions (being phased out due to toxicity)
- Starting material for organic synthesis teaching
- NMR spectroscopy standard (δ 7.26 ppm in CDCl₃ residual)
Former gasoline additive (removed due to toxicity); groundwater contaminant at industrial sites; VOC emission regulated.
Preparation and production
Industrial: catalytic reforming of petroleum naphtha (C₆-C₈ alkanes → benzene + H₂). Coal tar distillation (historical). Laboratory: decarboxylation of sodium benzoate with soda lime (small scale).
Global benzene production exceeds 50 million tonnes annually, almost entirely from petroleum processing.
Important reactions of Benzene
C₆H₆ + HNO₃ → C₆H₅NO₂ + H₂O
- Reaction type
- Electrophilic aromatic substitution (nitration)
- Conditions
- Mixed acid (HNO₃ + H₂SO₄), 50–60 °C
- Explanation
- NO₂⁺ electrophile substitutes one H on ring; aromaticity preserved. Nitrobenzene is TNT precursor.
- Products
- Nitrobenzene and water
- Why it matters
- Explosives, dyes, polyurethane intermediates
Related ideas: EAS · Electrophiles · Aromaticity
C₆H₆ + CH₃Cl → C₆H₅CH₃ + HCl
- Reaction type
- Friedel–Crafts alkylation
- Conditions
- AlCl₃ catalyst, heat
- Explanation
- CH₃⁺ electrophile (from CH₃Cl + AlCl₃) substitutes H, forming toluene (methylbenzene).
- Products
- Toluene and hydrogen chloride
- Why it matters
- Toluene production, alkylbenzene synthesis
Related ideas: Friedel–Crafts · Carbocations · Catalysts
2 C₆H₆ + 15 O₂ → 12 CO₂ + 6 H₂O
- Reaction type
- Combustion
- Conditions
- Ignition, excess oxygen
- Explanation
- Incomplete ventilation produces sooty flame due to high C:H ratio and aromatic stability releasing carbon clusters.
- Products
- Carbon dioxide and water
- Why it matters
- Energy content measurement, calorimetry
Related ideas: Combustion · Stoichiometry · Thermochemistry
C₆H₆ + 3 H₂ → C₆H₁₂
- Reaction type
- Catalytic hydrogenation
- Conditions
- Ni or Pt catalyst, 150–200 °C, high pressure
- Explanation
- Hydrogen adds across π system, destroying aromaticity to form cyclohexane — requires harsh conditions due to aromatic stability.
- Products
- Cyclohexane
- Why it matters
- Cyclohexane production for nylon industry
Related ideas: Hydrogenation · Aromatic stability · Catalysis
History and discovery
Faraday isolated benzene from illuminating gas (1825). Mitscherlich determined formula C₆H₆ (1834). Kekulé proposed ring structure (1865). Robinson and Hückel developed aromaticity theory (1920s–1930s). Occupational cancer link established mid-20th century.
Michael Faraday, 1825 — isolated 'bicarburet of hydrogen' from compressed oil gas residue.
Interesting facts
- Kekulé claimed the ring structure came to him in a dream of a snake biting its tail (1865).
- Benzene molar mass 78.11 g/mol — carbon content 92.3%, explaining sooty combustion.
- All six C–C bonds in benzene are equal length (1.39 Å), between single (1.54 Å) and double (1.34 Å).
- Benzene was once used as aftershave and dry cleaning solvent before toxicity was recognized.
Comparison with similar compounds
Benzene (C₆H₆, 78.11 g/mol) is aromatic and substitution-reactive; cyclohexane (C₆H₁₂, 84.16 g/mol) is saturated and undergoes typical alkane reactions.
Storage, handling, and safety
Store in flammable materials cabinet, away from ignition sources. Sealed containers in ventilated area. Never use benzene as general lab solvent in teaching settings.
Carcinogen — avoid all exposure. Use toluene or other safer solvents when possible. If unavoidable, use fume hood, nitrile gloves, and no skin contact. No eating or drinking in lab.
Known human carcinogen (leukemia); flammable; causes skin irritation and CNS depression at high inhalation levels.
- Carcinogenic (IARC Group 1)
- Flammable (flash point −11 °C)
- CNS depressant — dizziness, unconsciousness at high vapor levels
- Skin absorption and defatting dermatitis
Classification: GHS: Carc. 1A, Flam. Liq. 2, STOT RE 1
Exam notes and student tips
Exam notes
- Molar mass C₆H₆ = 6(12.01) + 6(1.008) = 78.11 g/mol.
- Aromaticity: planar, cyclic, conjugated, 4n+2 π electrons (n=1, so 6 π e⁻).
- EAS not addition — substitution preserves aromaticity (e.g., C₆H₆ + NO₂⁺ → C₆H₅NO₂ + H⁺).
- Combustion: 2 C₆H₆ + 15 O₂ → 12 CO₂ + 6 H₂O.
Student tips
- Use circle in ring to indicate delocalization in exam diagrams.
- Compare C₆H₆ (78.11) with C₆H₁₂ cyclohexane (84.16) — 6 fewer H means 3 double-bond equivalents.
- Link to Hückel rule: 4n+2 with n=1 → 6 π electrons.
Common mistakes
- Drawing alternating single/double bonds as fixed Kekulé structure instead of delocalized.
- Predicting addition reactions like alkenes — benzene prefers substitution.
- Confusing benzene with cyclohexane (C₆H₁₂, M = 84.16, saturated, not aromatic).
Misconceptions
- Kekulé structures with fixed double bonds are accurate — real benzene has equal bond lengths.
- All ring compounds are aromatic — cyclobutadiene (4 π e⁻) is antiaromatic and highly reactive.
- Benzene is safe at low exposure — it is a confirmed carcinogen with no established safe threshold.
Practice questions
1. Calculate the molar mass of benzene (C₆H₆).
Show answer
6(12.01) + 6(1.008) = 78.11 g/mol
2. How many moles of O₂ for complete combustion of 78.1 g benzene?
Hint: Balance: 2 C₆H₆ + 15 O₂ → 12 CO₂ + 6 H₂O.
Show answer
78.1 g = 1 mol C₆H₆; needs 15/2 = 7.5 mol O₂
3. Why does benzene undergo substitution rather than addition?
Show answer
Addition would destroy aromaticity (lose 150 kJ/mol resonance energy); substitution preserves the aromatic ring.
4. Verify benzene satisfies Hückel's rule.
Show answer
6 π electrons; 4n+2 with n=1 gives 6 — satisfies aromaticity criterion.
Frequently asked questions about Benzene
78.11 g/mol.
Chemistry of Benzene
The sections above give the number you need for calculations. Here we look more closely at how Benzene (C₆H₆) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.
Benzene (C₆H₆) is the archetypal aromatic hydrocarbon with molar mass 78.11 g/mol (6 × 12.01 + 6 × 1.008). Its planar hexagonal ring of sp²-hybridized carbons delocalizes six π electrons over six p orbitals, satisfying Hückel's 4n+2 rule (n=1) for aromatic stability. Resonance energy ~150 kJ/mol explains why benzene resists addition reactions that would destroy aromaticity, preferring substitution instead.
Benzene was first isolated from coal gas by Michael Faraday (1825). Its structure puzzled chemists until Kekulé proposed the ring (1865) and later the oscillating double-bond model. Modern molecular orbital theory describes fully delocalized π bonding. Benzene is a known human carcinogen (IARC Group 1) linked to leukemia from occupational exposure, yet remains indispensable for producing styrene, phenol, cumene (acetone + phenol), and nylon intermediates.
C₆H₆ shows equal numbers of carbon and hydrogen atoms — unusual among hydrocarbons and reflecting the ring structure where each carbon contributes one H. The empirical formula equals the molecular formula. Degree of unsaturation: (2×6+2−6)/2 = 4 (three double bonds equivalent or one ring + three double bonds).
Benzene undergoes electrophilic aromatic substitution (EAS): nitration (HNO₃/H₂SO₄), sulfonation (H₂SO₄), halogenation (FeCl₃ catalyst), Friedel–Crafts alkylation and acylation. It resists KMnO₄ oxidation and Br₂ addition under normal conditions. Burns with sooty flame: 2 C₆H₆ + 15 O₂ → 12 CO₂ + 6 H₂O.
Aromaticity and Hückel's Rule
Benzene's exceptional stability comes from complete delocalization of six π electrons around a planar, cyclic, conjugated ring, satisfying Hückel's 4n+2 rule (n = 1). This resonance stabilization (~150 kJ/mol) is why benzene resists the addition reactions typical of alkenes, instead undergoing substitution reactions that preserve the aromatic system — a foundational concept distinguishing aromatic from purely unsaturated hydrocarbons.
The Kekulé Structure and Its Limitations
August Kekulé's 1865 proposal of alternating single and double bonds in a hexagonal ring was a landmark advance, but it inaccurately implies two distinct bond lengths; X-ray studies later confirmed benzene has six identical C–C bonds (1.39 Å), intermediate between single and double bond lengths, reflecting true electron delocalization rather than rapidly oscillating discrete double bonds as Kekulé's dynamic model suggested.
Benzene as a Confirmed Human Carcinogen
Chronic occupational exposure to benzene is causally linked to acute myeloid leukemia and other blood disorders, leading IARC to classify it as a Group 1 carcinogen with no established safe exposure threshold; this has driven its removal from consumer products (perfumes, common solvents) and strict occupational exposure limits in industries where it cannot be entirely eliminated.
Benzene as a Petrochemical Feedstock
Despite its toxicity, benzene remains one of the most important industrial feedstocks, converted at massive scale into styrene (polystyrene, ABS plastics), phenol and acetone (via the cumene process), cyclohexane (nylon precursor), and aniline (dyes, polyurethanes) — meaning benzene's molecular fingerprint persists throughout much of the modern plastics and materials economy even though the free compound itself is tightly controlled.
Recalculate any formula with the molar mass calculator, compare atoms on the periodic table, or browse more compounds in the hydrocarbon library.
References and further reading
- IARC Monographs: Benzene carcinogenicity classification
- PubChem CID 241: Benzene structure and properties
- Clayden Organic Chemistry: Aromaticity and EAS mechanisms