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Phenolphthalein Omslag

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Understanding Phenolphthalein's Colour Change: A Deep Dive into its pH Indicator Properties



Phenolphthalein, a common laboratory chemical, is renowned for its dramatic colour change, a phenomenon often referred to as the "phenolphthalein omslag" (omslag being Dutch for "change" or "transition"). This article aims to explore this fascinating characteristic in detail, providing a comprehensive understanding of phenolphthalein's behaviour as a pH indicator, its chemical structure, its applications, and limitations.

1. The Chemical Structure and its Impact on Colour Change



Phenolphthalein's unique colour-changing properties stem from its complex organic structure. It exists in three primary forms, each exhibiting a distinct colour:

Colourless Lactone Form (Acidic pH): In acidic solutions (pH below 8.2), phenolphthalein exists primarily as a colourless lactone. This cyclic structure is relatively stable and doesn't absorb visible light in the range that our eyes perceive as colour.

Pink Carboxylate Ion Form (Basic pH): As the pH increases, hydroxide ions (OH⁻) from the base react with phenolphthalein, opening the lactone ring and forming a negatively charged carboxylate ion. This ion exhibits a quinoid structure, which is conjugated and thus absorbs light in the visible spectrum, resulting in a pink colour. The intensity of the pink colour increases with increasing pH.

Red Carboxylate Ion Form (Highly Basic pH): At extremely high pH values (above 12), phenolphthalein undergoes further changes and can exhibit a faint red or colourless form. This is due to a further change in the structure of the carboxylate ion.

The transition between these forms is what constitutes the phenolphthalein omslag, a sharp colour change from colourless to pink, typically occurring within a narrow pH range of approximately 8.2 to 10.0. This specific pH range makes it particularly useful for titrations involving weak acids and strong bases.

2. Phenolphthalein as a pH Indicator in Titrations



Titration is a crucial technique in analytical chemistry for determining the concentration of an unknown solution. Phenolphthalein's colour change serves as a visual indicator of the equivalence point – the point at which the acid and base have completely reacted.

Example: Titrating a solution of acetic acid (a weak acid) with sodium hydroxide (a strong base). Initially, the solution is colourless. As NaOH is added dropwise, the pH gradually increases. Once the equivalence point is reached (pH approximately 8.2-10.0), a single drop of NaOH can cause the solution to abruptly turn pink, signifying the completion of the reaction.

3. Applications Beyond Titrations



While titrations represent the most common application, phenolphthalein finds utility in other areas:

pH measurement: Though less precise than electronic pH meters, phenolphthalein can provide a rough estimate of pH within its sensitive range.

Laboratory demonstrations: Its dramatic colour change makes it an excellent tool for visually demonstrating acid-base reactions to students.

Medical applications (Historically): While largely obsolete, phenolphthalein was once used as a laxative due to its mild irritant properties on the intestinal tract. However, concerns regarding potential carcinogenic effects have led to its discontinuation for this use.

4. Limitations of Phenolphthalein



Despite its widespread use, phenolphthalein does have limitations:

Narrow pH range: Its colour change is limited to a specific pH range (8.2-10.0), making it unsuitable for titrations involving very weak acids or bases.

Slow response time in some cases: The colour change might not be instantaneous, especially in dilute solutions.

Sensitivity to temperature and solvent: The exact pH range of the colour change can slightly vary depending on temperature and the solvent used.


5. Conclusion



The phenolphthalein omslag, the distinctive colour change of phenolphthalein, is a crucial aspect of its functionality as a pH indicator. Its ability to visually signal the completion of acid-base reactions makes it indispensable in various analytical and educational contexts. While possessing limitations, the understanding of its chemical structure and behaviour provides a deeper appreciation for its applications and value in the scientific community.


FAQs



1. Is phenolphthalein toxic? While generally considered low toxicity, high concentrations can cause skin irritation. Appropriate safety precautions should always be followed when handling phenolphthalein.

2. Can phenolphthalein be used with all types of acids and bases? No, it's most effective with strong bases and weak to moderately strong acids. For very weak acids or bases, other indicators are more suitable.

3. Why does the colour change occur so abruptly near the equivalence point? The abrupt change is due to the rapid increase in pH at the equivalence point during a titration.

4. What are some alternative pH indicators? Methyl orange, bromothymol blue, and litmus paper are examples of alternative pH indicators with different pH ranges.

5. Where can I purchase phenolphthalein? Phenolphthalein is available from most chemical suppliers, but purchasing may require adherence to relevant regulations depending on your location and intended use.

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Phenolphthalein ACS reagent 77-09-8 - MilliporeSigma Phenolphthalein is an indicator for acid-base titration reactions. It changes from colorless to violet-red between pH 8.3-9.8, it is red in extremely acidic solutions, and colorless in extremely alkaline solutions. It is present as a nonionic, lipophilic lactone in aqueous neutral solutions.

Phenolphthalein | 77-09-8 - ChemicalBook 27 Jan 2025 · Phenolphthalein (CAS 77-09-8) information, including chemical properties, structure, melting point, boiling point, density, formula, molecular weight, uses, prices, suppliers, SDS and more, available at Chemicalbook.

Phenolphthalein: From Invisible Molecules to Visible Marvels Phenolphthalein is a chemical compound, often used as an indicator in titrations and its formula is C20H14O4. It is a weak acid that is partially soluble in water and is usually dissolved in alcohol for experimental applications.

Phenolphthalein Indicator: Working, Making & Colour - Infinity Learn The phenolphthalein indicator is a pH indicator solution that appears colorless in acidic and very alkaline conditions but turns fuchsia pink in normal alkaline conditions. This guide covers the colors seen at different pH levels, the chemical process behind the color change, how to create a phenolphthalein indicator, and its various uses.

Phenolphthalein - Kemi - Studieportalen.dk Hvordan kan det være at man bruger phenolphthalein ved stærk syre + stærk base (neutralisationsreaktionen)? Den har omslag fra 8,2 til 10, men ækvivalenspunktet er jo i 7,0 ?

Phenolphthalein - Structure, Properties, Synthesis and Uses Phenolphthalein is an indicator, based on whether it reaches an acid or a base, a chemical that changes colour. If it meets something basic, such as ammonia, it turns purple; if it meets an acid like vinegar or a neutral material like water, it remains colourless.

Phenolphthalein Indicator - Science Notes and Projects 19 Jan 2022 · Phenolphthalein indicator is a pH indicator solution that is colorless under acidic and extremely alkaline conditions and fuchsia pink under ordinary alkaline conditions. Here is a look at the colors at different pH ranges, the chemistry of the color change, how to make phenolphthalein indicator, and uses of the chemical.

Phenolphthalein - Wikipedia Phenolphthalein (/ f ɛ ˈ n ɒ l (f) θ ə l iː n / [citation needed] feh-NOL(F)-thə-leen) is a chemical compound with the formula C 20 H 14 O 4 and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations.

Phenolphthalein | C20H14O4 | CID 4764 - PubChem Phenolphthalein | C20H14O4 | CID 4764 - structure, chemical names, physical and chemical properties, classification, patents, literature, biological activities, safety/hazards/toxicity information, supplier lists, and more.

Phenolphthalein Indicator: Synthesis, Uses, Properties, Preparation 10 Feb 2023 · Phenolphthalein is an organic compound that serves as a laboratory reagent and pH indicator. It stimulates the intestinal mucosa and constricts smooth muscles, causing laxative effects. The fact that phenolphthalein may be carcinogenic, however, has led to …

Phenolphthalein - an overview | ScienceDirect Topics Phenolphthalein is widely used as an acid-base indicator. It is a definite chemical compound, colorless in acid solutions and red or pink in alkaline liquids. • While phenolphthalein undergoes photodegradation in the air and is not considered dangerous for the ozone layer, it is a severe water pollutant. •

FAM-LAX PHENOLPHTHALEIN TABLETS - Patient info Phenolphthalein is a diphenylmethane stimulant laxative. Up to 15% of phenolphthalein given by mouth is absorbed. Enterohepatic circulation occurs and the active glucuronide is excreted in the bile. Some excretion occurs in the urine.

Phenolphthalein - Chemistry Online 22 Apr 2024 · Phenolphthalein (molecular formula C 20 H 14 O 4) is a pH indicator. In acidic solutions it remains colorless, but in the presence of basic solutions it takes on a pinkish color with a turning point between pH = 8.0 (colorless) to pH = 9.8 ( magenta or pinkish ).

Phenolphthalein: Uses, Interactions, Mechanism of Action 11 Sep 2007 · Phenolphthalein is a drug used for symptomatic relief of constipation and bowel cleansing prior to medical procedures. Generic Name Phenolphthalein DrugBank Accession Number DB04824 Background. Phenolphthalein was withdrawn in Canada due to concerns with carcinogenicity in 1997. Type Small Molecule Groups

Phenolphthalein | Magnificent molecules - RSC Education 24 Dec 2018 · Painting on a solution of phenolphthalein is an easy way to check for the extent of carbonation inside a concrete slab: pink areas are alkaline and uncarbonated while carbonated areas will remain unstained, suggesting there is a problem.

Phenolphthalein - Structure, Properties, Uses of C20H14O4 Phenolphthalein, an organic compound with the chemical formula C20H14O4, is a weak acid which can be used as an indicator for acid-base titrations. In acidic solutions, the compound is colourless. It is pinkish in simple solutions (with the transition occurring around pH 9).

Phenolphthalein - chemeurope.com Phenolphthalein is synthesized by condensation of phthalic anhydride with two equivalents of phenol under acidic conditions (hence the name). It was discovered in 1871 by Adolf von Baeyer. Uses. Phenolphthalein has been used for over a century as a laxative, but is now being removed from the market because of concerns over carcinogenicity ...

Phenolphthalein – Structure and Why it Changes Color? - Toppr Phenolphthalein is naturally colourless and works differently then litmus paper. Also, it turns in pink colour in an alkaline solution or base. Moreover, the compound remains colourless in acids but starts to turn pink on pH 8.2 and continues to turn bright purple in strong bases.

Phenolphthalein: Structure, Properties, pH Indicator and Uses ... 6 Feb 2024 · Phenolphthalein (C20H14O4) is an organic chemical compound often used as an indicator in acid-base titrations. Learn more about phenolpththalein and how is it used as indicator in detail in this article

Phenolphthalein Omslag The phenolphthalein omslag, the distinctive colour change of phenolphthalein, is a crucial aspect of its functionality as a pH indicator. Its ability to visually signal the completion of acid-base reactions makes it indispensable in various analytical and educational contexts.