Molar Mass of Aspirin (C₉H₈O₄)

Each row shows how much mass one element contributes to the total for C₉H₈O₄.

Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Aspirin (C₉H₈O₄).

Without looking above, write the atom count for C₉H₈O₄, then compute the molar mass. Check your answer against 180.159 g/mol.

Next challenge: how many grams are in 0.250 mol of Aspirin? Multiply 0.250 × 180.159 to get 45.040 g.

Irreversibly inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin and thromboxane synthesis; used for pain relief, fever reduction, inflammation control, and long-term cardiovascular event prevention.

Preparation and production

Synthesized by reacting salicylic acid with acetic anhydride in the presence of a small amount of acid catalyst (sulfuric or phosphoric acid), which acetylates the phenolic hydroxyl group. The crude product is purified by recrystallization, typically from ethanol-water mixtures, to yield pharmaceutical-grade acetylsalicylic acid crystals.

Global aspirin production is estimated in the tens of thousands of tonnes annually, supplying both over-the-counter analgesic markets and the large and growing low-dose cardiovascular prophylaxis market.

Felix Hoffmann, working at Bayer, first synthesized a stable, pure form of acetylsalicylic acid in 1897, building on decades of prior salicylic acid chemistry dating to Charles Frédéric Gerhardt's 1853 synthesis. Bayer marketed the compound as Aspirin starting in 1899, and it quickly became one of the most widely used drugs in the world. Its mechanism of action remained a mystery until John Vane's landmark 1971 discovery that aspirin inhibits prostaglandin synthesis via cyclooxygenase, work that earned him a share of the 1982 Nobel Prize.

Felix Hoffmann, Bayer, 1897 — synthesized a stable, purified form of acetylsalicylic acid; mechanism of action elucidated by John Vane in 1971.

Interesting facts

• Aspirin's antiplatelet effect from a single dose can last the entire 7–10 day lifespan of an affected platelet because it acetylates the enzyme irreversibly.
• John Vane won a share of the 1982 Nobel Prize in Physiology or Medicine for discovering how aspirin inhibits prostaglandin synthesis, nearly a century after the drug's introduction.
• Willow bark, aspirin's distant natural ancestor, was used for pain relief as far back as ancient Egyptian and Greek medicine.
• Bayer's trademark 'Aspirin' name became so widely used that it was declared a generic term in several countries following World War I reparations agreements.

Comparison with similar compounds

Aspirin (C₉H₈O₄, 180.16 g/mol) shares its aromatic-acid core with salicylic acid (C₇H₆O₃, 138.12 g/mol) but differs pharmacologically by irreversibly inhibiting cyclooxygenase, unlike reversible NSAIDs such as ibuprofen (C₁₃H₁₈O₂, 206.28 g/mol).

Store in a cool, dry place in tightly sealed, moisture-resistant packaging to minimize hydrolytic degradation. Discard tablets that develop a strong vinegar-like odor, indicating significant breakdown to salicylic and acetic acid.

Generally safe at recommended pharmaceutical doses; handle bulk powder with standard gloves and avoid inhaling dust. Overdose or hypersensitivity reactions require medical attention; avoid use in children with viral illness due to Reye's syndrome risk.

Safe and effective at recommended therapeutic doses; overdose can cause salicylate toxicity, and use is contraindicated or restricted in certain populations (children with viral illness, some bleeding disorders).

• Gastrointestinal irritation and bleeding risk, especially with prolonged or high-dose use
• Salicylate toxicity (tinnitus, hyperventilation, metabolic acidosis) with overdose
• Reye's syndrome risk in children and teenagers with viral illness
• Increased bleeding risk due to antiplatelet effect

Classification: Regulated as an over-the-counter and prescription drug product; not classified as an industrial hazardous chemical at pharmaceutical-grade use levels

1. 1. Calculate the molar mass of aspirin (C₉H₈O₄).

   Show answer

   9(12.01) + 8(1.008) + 4(16.00) = 180.16 g/mol

2. 2. What is the theoretical yield of aspirin from 2.00 g of salicylic acid with excess acetic anhydride?

   Show answer

   2.00 g ÷ 138.12 g/mol = 0.01448 mol salicylic acid → 0.01448 mol aspirin × 180.16 g/mol ≈ 2.61 g

3. 3. How many moles of aspirin are in a standard 325 mg tablet (assuming pure active ingredient)?

   Show answer

   0.325 g ÷ 180.16 g/mol ≈ 1.80 × 10⁻³ mol

4. 4. Why does aspirin's antiplatelet effect last longer than its analgesic effect after a single dose clears the bloodstream?

   Show answer

   Aspirin irreversibly acetylates COX-1 in platelets, which cannot synthesize new enzyme (lacking a nucleus), so the effect persists for the platelet's full ~10-day lifespan even after the drug itself is metabolized.

• Salicylic AcidC₇H₆O₃

The sections above give the number you need for calculations. Here we look more closely at how Aspirin (C₉H₈O₄) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.

Aspirin, chemically acetylsalicylic acid (C₉H₈O₄), has molar mass 180.16 g/mol (C 9 × 12.01 + H 8 × 1.008 + O 4 × 16.00) and is produced by acetylating the phenolic hydroxyl group of salicylic acid with acetic anhydride. This single acetyl substitution transforms a compound that is notably irritating to the stomach lining into one of the most widely used and best-tolerated medicines in history, while retaining and even extending its pharmacological versatility as an analgesic, antipyretic, anti-inflammatory, and antiplatelet agent.

Aspirin's therapeutic effects trace to a single, precisely understood molecular mechanism: it irreversibly acetylates a serine residue in the active site of cyclooxygenase (COX) enzymes, permanently blocking their ability to convert arachidonic acid into prostaglandins and thromboxanes. Because COX-1 in platelets cannot synthesize new enzyme (platelets lack a nucleus), a single aspirin dose suppresses platelet aggregation for the platelet's entire ~10-day lifespan — the pharmacological basis for aspirin's use in low-dose regimens to prevent heart attacks and strokes, a role entirely distinct from its higher-dose use as a pain and fever reliever.

First marketed by Bayer in 1899 following Felix Hoffmann's synthesis, aspirin remains chemically simple yet mechanistically rich enough to have earned John Vane a share of the 1982 Nobel Prize in Physiology or Medicine for elucidating its prostaglandin-based mode of action decades after its introduction. In aqueous or humid storage conditions, aspirin slowly hydrolyzes back into salicylic acid and acetic acid — the source of the faint vinegar-like smell sometimes detected in old, degraded tablets — a reminder that its ester linkage, while pharmacologically crucial, is also its chemical vulnerability.

C₉H₈O₄ represents salicylic acid's benzene ring with an acetyl ester (–OCOCH₃) replacing the original phenolic hydroxyl, alongside the unmodified carboxylic acid group. The formula reflects two distinct oxygen-containing functional groups: an ester linkage (from acetylation) and a carboxylic acid, both attached to the aromatic ring in an ortho relationship inherited from the salicylic acid precursor.

Aspirin is a weak monoprotic acid at its carboxyl group (pKa 3.5) and is chemically an ester at its acetyl-oxygen linkage, making it susceptible to hydrolysis in moist conditions or basic solution, reverting to salicylic acid and acetic acid. It reacts with bases to form soluble acetylsalicylate salts, and its irreversible acetylation of the COX enzyme's active-site serine residue (via nucleophilic attack transferring the acetyl group) is the molecular basis of its pharmacological action — chemically identical in principle to esterase-mediated acetyl transfer reactions elsewhere in organic chemistry.

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• PubChem CID 2244: Aspirin (acetylsalicylic acid) compound data
• Nobel Prize Foundation: John Vane's 1982 prize for prostaglandin research
• NIST Chemistry WebBook: Thermodynamic properties