Theories of Acid Base Indicators| Acid Base Titrations| Pharmaceutical Analysis(unit-2)| Pharma Hub+ скачать в хорошем качестве

Theories of Acid Base Indicators| Acid Base Titrations| Pharmaceutical Analysis(unit-2)| Pharma Hub+

Hello friends, welcome to the channel Pharma Hub + I'm Krishna Agrahari & I'll start the 2nd unit of Pharmaceutical Analysis that is Acid Base Titration. In this video you will get to know the theories of acid base indicators. Indicators are the substance used in a reaction to determine the endpoint of the reaction by changing their colors. They change their color between a certain pH range. For example Phenolphthalein is a colourless weak acid, has a pH range of 8.0 - 9.5. In the solutions having pH less than 8.0 the phenolphthalein will remain colourless when added to the solution & If the solution has a pH more than 9.5, it changes its color into pink. There are two theories that tell how indicators behave i.e., how the change their color 1. Ostwald Theory 2. Quinonoid Theory 1. Ostwald theory According to this theory, acid base indicator is either a weak acid and or a weak base. The unionised molecules of the indicators in the solution are of one color and the ions obtained by their separation are of another color. for example- phenolphthalein is a weak acid. It is colourless. On dissolving it in water, it is ionised into colourless H+ ions and pink anions. In the presence of H ions in acidic medium, the ionisation of HPh is very low due to the common ion effect, that is, the concentration of Ph- is very low and the solution remains colourless. In alkaline medium, OH- ion obtained from the base combines with H+  ions obtained from HPh to form water. Water is a weak electrolyte and its ionisation is very small. This theory also clears that phenolphthalein is not a good indicator for the titration of strong acids and weak bases. 2. Quinonoid Theory This theory is a modern theory to explain the working of indicators. According to this theory, indicator aromatic carbonic compounds used in acid base titrations are. They are a mixture of at least two movable forms. Among these, one form is in acidic medium and the other form in alkaline medium in greater proportion. These two forms are called benzenoid and quinonoid forms. Both these forms have different colors. The color of the quinonoid form is darker than the color of the benzenoid form. Therefore, when the pH value of a solution changes, there is a change in the benzenoid form to the quinonoid form or the quinonoid form to the benzenoid form causing a change in color. Thank you for watching stay tune with us !! +++++++++++++++++++++++++++++++++++++++++ Like our Facebook Page   / hubofpharma   Join our Facebook Group https://www.facebook.com/groups/90660... +++++++++++++++++++++++++++++++++++++++++ #theoriesofacidbaseindicators #acidbasetitration #ostwaldtheory #quinonoidtheory #pharmaceuticalanalysis #pharmahub+ #krishnaagrahari #phenolphthaleincolorchange