Molar Mass of Salicylic Acid (C₇H₆O₃)

Each row shows how much mass one element contributes to the total for C₇H₆O₃.

Save a printable summary, revision sheet, practice worksheet, or laboratory reference for Salicylic Acid (C₇H₆O₃).

Without looking above, write the atom count for C₇H₆O₃, then compute the molar mass. Check your answer against 138.122 g/mol.

Next challenge: how many grams are in 0.250 mol of Salicylic Acid? Multiply 0.250 × 138.122 to get 34.531 g.

Naturally occurring plant defense hormone triggering systemic acquired resistance; topically active keratolytic agent in human dermatology.

Preparation and production

Industrially produced by carboxylation of phenol via the Kolbe–Schmitt reaction: sodium phenoxide reacts with carbon dioxide under heat and pressure, followed by acidification to yield salicylic acid. It can also be obtained by hydrolysis of methyl salicylate (oil of wintergreen) or oxidation of salicylaldehyde.

Global production supplies both the pharmaceutical sector (as aspirin precursor) and the larger dermatological and cosmetic ingredient market; production is dominated by the Kolbe–Schmitt carboxylation route from phenol and CO₂.

Willow bark extracts containing salicin were used medicinally in ancient Egypt, Greece (Hippocrates recommended willow leaf tea for pain and fever), and other traditional medicine systems for millennia. Johann Andreas Buchner isolated salicin in 1828, and Raffaele Piria converted it to salicylic acid in 1838. Hermann Kolbe achieved the first synthetic route in 1859, enabling industrial-scale production that eventually fed Felix Hoffmann's 1897 synthesis of acetylsalicylic acid (aspirin) at Bayer.

Salicin isolated by Johann Andreas Buchner in 1828; salicylic acid derived from it by Raffaele Piria in 1838; first synthesized industrially by Hermann Kolbe in 1859.

Interesting facts

• Salicylic acid takes its name from Salix, the botanical genus of willow trees, whose bark contains the natural precursor salicin.
• Aspirin was developed specifically to reduce the gastric irritation caused by salicylic acid itself, while retaining its pain-relief action.
• Plants use salicylic acid as an internal chemical signal to warn distant tissues of an ongoing pathogen attack.
• The ferric chloride test turns salicylic acid solutions a striking violet-purple, a reaction still used to identify phenolic compounds in teaching labs.

Comparison with similar compounds

Salicylic acid (C₇H₆O₃, 138.12 g/mol, pKa 2.97) is more acidic than benzoic acid (C₆H₅COOH, 122.12 g/mol, pKa 4.20) because the ortho hydroxyl group's intramolecular hydrogen bonding and inductive effect stabilize the carboxylate conjugate base.

Store in a cool, dry place away from light in tightly closed containers. Stable under normal conditions; avoid strong oxidizers and bases that could hydrolyze or otherwise alter the compound over long storage.

Mild irritant to skin, eyes, and respiratory tract at high concentrations or as dust. Use gloves and eye protection when handling concentrated solutions or bulk powder; avoid excessive topical application given systemic absorption risk (salicylate toxicity) at high doses.

Generally safe at approved topical dermatological concentrations; excessive or widespread topical use, or oral ingestion, can cause salicylate toxicity.

• Skin, eye, and respiratory irritation from concentrated powder or solution
• Salicylate toxicity (nausea, tinnitus, hyperventilation) if ingested in quantity or over-applied topically
• Reye's syndrome risk in children when related salicylates are taken during viral illness

Classification: GHS: Skin Irrit. 2, Eye Irrit. 2 (concentrated material); topical formulations regulated as OTC drug products

1. 1. Calculate the molar mass of salicylic acid (C₇H₆O₃).

   Show answer

   7(12.01) + 6(1.008) + 3(16.00) = 138.12 g/mol

2. 2. How many grams of aspirin can theoretically form from 13.81 g of salicylic acid with excess acetic anhydride?

   Show answer

   13.81 g ÷ 138.12 g/mol = 0.100 mol salicylic acid → 0.100 mol aspirin × 180.16 g/mol = 18.02 g (theoretical yield)

3. 3. Why is salicylic acid a stronger acid than benzoic acid?

   Show answer

   The ortho hydroxyl group forms an intramolecular hydrogen bond and exerts an inductive effect that stabilizes the negative charge on the conjugate base, increasing acidity (lower pKa).

4. 4. What color does salicylic acid give with ferric chloride, and what does this indicate?

   Show answer

   A violet-purple color, indicating the presence of a phenolic hydroxyl group.

• AspirinC₉H₈O₄

The sections above give the number you need for calculations. Here we look more closely at how Salicylic Acid (C₇H₆O₃) behaves chemically—so the molar mass connects to real reactions, properties, and laboratory practice.

Salicylic acid (C₇H₆O₃) is an aromatic hydroxy acid with molar mass 138.12 g/mol (C 7 × 12.01 + H 6 × 1.008 + O 3 × 16.00), consisting of a benzene ring bearing both a carboxylic acid group and an adjacent (ortho) hydroxyl group. This ortho arrangement allows an internal hydrogen bond between the two functional groups, which strengthens the acid (pKa 2.97, notably more acidic than benzoic acid's 4.20) and lowers its melting point and volatility relative to the meta and para hydroxybenzoic acid isomers.

Salicylic acid is best known as the direct chemical precursor to aspirin: reacting it with acetic anhydride acetylates the phenolic hydroxyl group to produce acetylsalicylic acid, converting a locally irritating compound into the far gentler, widely tolerated analgesic that transformed medicine in the late 19th century. Salicylic acid itself remains in wide topical use — its keratolytic action (breaking down the protein bonds that hold dead skin cells together) makes it a mainstay ingredient in acne treatments, wart removers, dandruff shampoos, and corn/callus plasters, working by gently dissolving the outer layer of hardened or excess skin.

Beyond pharmacology, salicylic acid connects to plant biology as a close chemical relative of the plant hormone system: plants synthesize salicylic acid and its derivatives as signaling molecules that trigger systemic acquired resistance, priming the plant's defenses against pathogens — a role echoing willow bark's ancient use as a folk remedy, since salicylic acid derivatives (salicin) occur naturally in willow (Salix) bark and were the original source from which the compound takes its name.

C₇H₆O₃ contains a benzene ring with two substituents in the ortho (1,2) relationship: a carboxylic acid (–COOH) and a hydroxyl (–OH) group. This close spatial arrangement permits an intramolecular hydrogen bond between the hydroxyl oxygen and the carbonyl oxygen of the carboxyl group, a structural feature that distinguishes salicylic acid's chemistry and physical properties from its meta- and para-hydroxybenzoic acid isomers, which share the same molecular formula but cannot form this internal bond.

Salicylic acid is a weak monoprotic acid at its carboxyl group (pKa 2.97) with a separately, much more weakly acidic phenolic hydroxyl (pKa ~13.4). It undergoes esterification at the carboxyl group (methyl salicylate, oil of wintergreen) and acetylation at the hydroxyl group (aspirin synthesis) — two different reactive sites giving two very different classes of derivatives. It gives a characteristic purple-violet color with ferric chloride solution, a classic qualitative test for phenolic compounds.

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• PubChem CID 338: Salicylic acid compound data
• NIST Chemistry WebBook: Thermodynamic properties
• Royal Pharmaceutical Society: Salicylate pharmacology and history