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Phenolphthalein is used in toys, for example as a component of disappearing inks, or disappearing dye on the "Hollywood Hair" Barbie hair. In the ink, it is mixed with sodium hydroxide, which reacts with carbon dioxide in the air. This reaction leads to the pH falling below the color change threshold as hydrogen ions are released by the reaction:
In order to generate the intense pink color indicative of a positive test, the reduced phenolphthalein must be oxidized back to its normal, colored form. In the relevant reaction, hydrogen peroxide reacts with the hemoglobin in the blood. Phenolphthalein does not directly participate in this process; instead, it acts as an external source of ...
Colorimetric analysis is a method of determining the concentration of a chemical element or chemical compound in a solution with the aid of a color reagent.It is applicable to both organic compounds and inorganic compounds and may be used with or without an enzymatic stage.
Since phenolphthalein molecules are surrounded by the polymers and thus left on the surface even after another rinse, the test strip turns red when a base is added. (Figure 1d) On the other hand, if the patient’s sample does not include any targeted antigens, the sandwiched binding complexes on the surface will not be formed, which leads to ...
In a titration of a weak acid with a strong base the pH rises more steeply as the end-point is approached. At the end-point, the slope of the curve of pH with respect to amount of titrant is a maximum. Since the end-point occurs at pH greater than 7, the most suitable indicator to use is one, like phenolphthalein, that changes color at high pH. [2]
As with all presumptive tests, this technique can produce false positive results due to metals and strong chemicals, such as bleach, that will also react. Another common presumptive test is the Kastle-Meyer or Phenolphthalein test. This is a catalytic test that detects the heme group in blood that transports oxygen and carbon dioxide. [5]
As we wait to see what 2025 has in store, it's clear that climate change has taken its toll already. Scroll through the images below to see what we consider the most impactful weather photos of 2024.
A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. [1] It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex. Complexometric indicators are also known as pM indicators.