Tartaric Acid
Properties
| State | Solid at room temperature |
| Color | White crystalline powder |
| Solubility | Highly soluble in water (133 g/100 mL at 20°C) |
| Melting Point | 171°C (L-tartaric acid) |
| Boiling Point | Decomposes before boiling |
About Tartaric Acid
Tartaric acid is a dicarboxylic acid (C4H6O6, 150.086 g/mol) with two adjacent hydroxyl groups on a four-carbon backbone, and it carries more historical weight than almost any other small molecule in organic chemistry. In 1848, a 25-year-old Louis Pasteur sat at a microscope picking apart sodium ammonium tartrate crystals with tweezers and noticed that the hemihedral facets pointed in two different directions. Separating them by hand and dissolving each pile in water gave solutions that rotated polarized light in opposite directions — the experiment that founded stereochemistry. The molecule has two stereocenters and shows up as L-tartaric acid (the natural form in grapes), D-tartaric acid, and the achiral meso form. Wineries deal with it constantly: as a fermenting must cools, potassium bitartrate (cream of tartar) crystallizes out as the gritty 'wine diamonds' on the underside of corks and inside barrels. Modern pharmaceutical synthesis uses the L-form as a chiral resolving agent — adding it to a racemic amine produces diastereomeric salts that crystallize separately, which is how generic metoprolol and several other single-enantiomer drugs are isolated.
Where you'll encounter it
If you've ever made a meringue and added a pinch of cream of tartar to stabilize the egg whites, that's potassium bitartrate doing its job by lowering the pH and helping the proteins denature into a stable foam. Anyone who has tasted a Sour Patch Kid or a Warheads candy has met tartaric acid directly — it's the sharper, more lingering acid that food manufacturers reach for when citric acid feels too soft. In a teaching lab, the classic Fehling's-test variant for reducing sugars uses Rochelle salt (sodium potassium tartrate) as the chelator that keeps Cu(II) in solution at high pH. Winemakers monitor tartrate levels obsessively because cold-stabilizing a finished wine to drop excess potassium bitartrate before bottling is the difference between a clear bottle and one that grows visible crystals on the shelf.
Common Uses
- Acidulant in hard candies, sour gummies, and carbonated soft drinks for sharp tang
- Cream of tartar (potassium bitartrate) for stabilizing meringues and activating baking soda
- Chiral resolving agent for separating racemic amines into single-enantiomer pharmaceutical APIs
- Acidity adjustment and tartrate cold-stabilization in winemaking
- Rochelle salt component in Fehling's reagent and silvered-mirror plating baths
- Effervescent tablet acid paired with sodium bicarbonate (Alka-Seltzer chemistry)
- Chelating agent in electroplating baths to keep copper and silver in solution at high pH
Safety Information
Low toxicity and FDA GRAS for food use up to typical confection levels (around 1.5%). Oral LD50 in rats is roughly 7.5 g/kg. Human gastrointestinal upset, including diarrhea and cramping, appears at gram-scale ingestion; reports of acute tubular necrosis exist at multi-gram doses. GHS classifications cover eye irritation (Category 2A) and respiratory irritation from inhaled dust. No OSHA PEL is set specifically, but standard PNOC limits apply (15 mg/m3 total dust). Lab handling needs only goggles, gloves, and dust mask for bulk operations. The L-form occasionally crystallizes from saturated solutions on glassware as needles that look like sugar — label clearly.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.