Overview
Phenolphthalein solution is a versatile chemical indicator primarily used to detect pH changes in aqueous solutions. It transitions from colorless (acidic/neutral pH) to pink/fuchsia (basic pH) at a range of 8.3–10.0, making it ideal for titration experiments. First synthesized in 1871 by Adolf von Baeyer, it gained prominence due to its sharp endpoint visibility. While its use in laxatives has declined due to safety concerns, it remains a staple in laboratories and educational settings for its reliability and ease of use.
Physical and Chemical Properties
Phenolphthalein is an organic compound with the formula C20H14O4. In solution, it exhibits high solubility in alcohols and alkaline media but limited solubility in water. The indicator’s color change is reversible and depends on protonation/deprotonation of its hydroxyl groups. Its stability is compromised by prolonged exposure to light or strong oxidizers, which may degrade the compound. Density approximates water (1.0 g/cm³), and it has negligible volatility. The solid form melts at 258–263°C but decomposes upon further heating.
Main Applications
The solution is indispensable in acid-base titrations, particularly for weak acid-strong base reactions where a clear endpoint is critical. It’s also used in chemistry education to demonstrate pH concepts and in quality control for alkaline substance testing. Industrially, diluted phenolphthalein solutions aid in monitoring wastewater treatment processes. Historically, it served as an active ingredient in over-the-counter laxatives, though this application has been discontinued in many countries due to potential carcinogenicity concerns at high doses.
Safety and Storage
While diluted phenolphthalein solutions pose minimal risk, concentrated forms may irritate skin and eyes. Always use personal protective equipment (PPE) such as nitrile gloves and goggles when handling. Store in amber glass bottles to prevent photodegradation, ideally at 15–25°C. Shelf life typically exceeds two years if uncontaminated. Avoid contact with strong oxidizers like peroxides, which may react violently. Spills should be neutralized with dilute acid before disposal.
B2B Procurement Guide
When procuring phenolphthalein solution, specify concentration (common range: 0.5–1% w/v in ethanol/water) and verify CAS 77-09-8 to ensure authenticity. Bulk buyers should request certificates of analysis (CoA) for purity and solvent composition. Prices vary by volume and supplier; expect $10–$50 per liter for standard solutions. Ethanol-based formulations are preferable for stability. Consider suppliers compliant with ISO 9001 or equivalent standards for consistent quality. For educational use, pre-packaged dropper bottles may offer convenience.
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