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Phenolphthalein Indicator 1% in IPA

$45.76
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SKU: ZP0523-16
California prop 65
Description
  • What it is. This phenolphthalein indicator is a 1% solution in isopropyl alcohol (IPA), available in 1 pint and 20 L sizes. It is the classic colorless-to-pink indicator for titrating acids with strong bases.
  • How the color change works. Phenolphthalein is colorless below about pH 8.2 and turns pink to fuchsia above about pH 10. In a titration of acid with sodium or potassium hydroxide, the first persistent faint pink marks the endpoint.
  • Chemical identity. Phenolphthalein (CAS 77-09-8, C20H14O4, 318.32 g/mol) is a triphenylmethane dye. In base, it loses protons and opens its lactone ring to form the colored form; in strongly basic solution, it slowly fades back to colorless.
  • Why it is dissolved in alcohol. Phenolphthalein is only slightly soluble in water but dissolves readily in alcohols. A 1% solution in isopropyl alcohol stays clear and stable and disperses quickly into the titration sample.
  • Where its endpoint is useful. Because it changes color near pH 8.2 to 10, phenolphthalein suits titrations of strong and weak acids with strong bases, such as acetic acid in vinegar, acid value in oils, and standardizing sodium hydroxide with potassium hydrogen phthalate.
  • Standardizing sodium hydroxide. Phenolphthalein is the standard indicator for standardizing sodium or potassium hydroxide against potassium hydrogen phthalate, a stable primary standard acid. Lab Pro's Potassium Hydroxide 0.1 N Solution, 1 Gallon is one base commonly checked this way.
  • Phenolphthalein alkalinity. In water analysis, titrating with acid to the phenolphthalein endpoint near pH 8.3 measures phenolphthalein alkalinity, mainly hydroxide plus half the carbonate. Continuing to the methyl orange endpoint gives total alkalinity; see Lab Pro's Methyl Orange Indicator, 0.1% (w/v) Aqueous.
  • Two sizes. The 1 pint size (ZP0523-16) suits teaching labs and benchtop titration, while the 20 L size (ZP0523-640) supports QC labs and production testing with high titration volumes.
  • Flammability and handling. Because the solvent is isopropyl alcohol, the solution is flammable. Keep it away from heat and flames. Phenolphthalein is treated as a suspected carcinogen, so avoid ingestion and skin contact; wear gloves.
  • Where it is used. Phenolphthalein is used in acid-base titrations in teaching, QC, and food labs; for acid value and free fatty acid testing of oils; for alkalinity in water; for concrete carbonation testing; and in demonstrations of pH indicators.

Technical Specifications

Chemical Name Phenolphthalein, 1% solution in isopropyl alcohol
CAS Numbers 77-09-8 (phenolphthalein); 67-63-0 (isopropyl alcohol)
Synonyms (dye) 3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone
Formula (dye) C20H14O4
Molecular Weight (dye) 318.32 g/mol
Concentration 1% phenolphthalein
Solvent Isopropyl alcohol
Transition Range pH 8.2 (colorless) to about 10 (pink to fuchsia)
Typical Endpoint First persistent faint pink
Appearance Clear, colorless liquid
Flash Point (IPA solvent) About 12 °C
Typical Dose 2 to 3 drops per titration
Hazard Profile Flammable liquid; phenolphthalein is a suspected carcinogen (confirm on SDS)
DOT Confirm on SDS (flammable IPA-based solution)
Package Sizes 1 pint; 20 L

Available Variants

  • ZP0523-16: 1 pint for teaching labs and benchtop titration.
  • ZP0523-640: 20 L for QC labs and high-volume testing.

Applications / Common Uses

  • Acid-base titration: Indicates strong-base titration endpoints.
  • NaOH standardization: Signals the KHP standardization endpoint.
  • Acid value of oils: Indicates free fatty acid titrations.
  • Water alkalinity: Marks the phenolphthalein alkalinity endpoint.
  • Concrete carbonation: Shows carbonated (colorless) versus alkaline (pink) concrete.

Storage, Handling & Shipping

Caution: This solution is flammable because it contains isopropyl alcohol. Phenolphthalein is a suspected carcinogen. Keep away from heat and flames; avoid ingestion and skin contact; wear safety glasses and gloves.

Store tightly closed in a cool, well-ventilated flammables area away from heat, sparks, open flames, and oxidizers. Dispense small amounts into a dropper vessel for use, and never return used indicator to stock.

  • Incompatible materials: Strong oxidizers and strong bases.
  • Personal protection: Safety glasses and gloves.
  • Spill response: Remove ignition sources and absorb with non-combustible material.
  • First aid: Eyes: rinse for several minutes. Skin: wash with soap and water. Ingestion: seek medical advice.

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FAQs

What color is phenolphthalein in acid and base?

Phenolphthalein is colorless in acidic and neutral solutions and turns pink to fuchsia above about pH 8.2 to 10. In strongly basic solutions, it slowly fades back to colorless, so titrate promptly and record the first persistent faint pink as the endpoint. Judge it against a white background.

Why is phenolphthalein dissolved in isopropyl alcohol?

Phenolphthalein dissolves poorly in water but readily in alcohols. A 1% solution in isopropyl alcohol stays clear and stable, and it mixes quickly into the sample. The alcohol makes the solution flammable, so keep it away from heat and open flames. Store it in a flammable area.

What titrations use phenolphthalein?

It is used to titrate acids with strong bases, standardize sodium hydroxide with potassium hydrogen phthalate, measure acetic acid in vinegar, test acid value and free fatty acids in oils, and determine phenolphthalein alkalinity in water. Its endpoint suits weak acids titrated with strong bases.

Is phenolphthalein safe to use?

At indicator strength in small drops, exposure is low, but phenolphthalein is treated as a suspected carcinogen, and the solvent is flammable. Wear gloves and safety glasses, avoid ingestion and skin contact, and use it away from heat. It was once a laxative but was withdrawn over safety concerns.

Which size should I choose?

Choose the 1 pint for teaching labs and benchtop titration, where it is used up while fresh. Choose the 20 L for QC labs and production testing with high titration volumes, dispensing smaller working amounts into dropper vessels for daily use. Both sizes contain the same solution.