Question

Does Phenopthalein or methyl orange makes any chemical changes in a reaction.?

Answer 1

Yes, they have different structure in acidic and in basic medium.

Phenolphthalein is a chemical compound (formula of C₂₀ H₁₄O₄). It is colourless but it turns pink in alkaline solutions. It happens because it undergoes ionization on addition/removal of positively (H⁺) or negatively charged ions (OH^-), which converts the molecule into ions. When phenolphthalein molecule contains H⁺ ions it is naturally colourless. When exposed to an alkaline solution, these hydrogen ions are removed, and phenolphthalein molecule gets ionized and the solution turns pink. The stronger is the alkali solution, more hydrogen ions removed and stronger pink colour of the phenolphthalein solution.

Methyl orange is a halochromic (changes colour with change in pH of solution) substance, with molecular formula C₁₄H₁₄N₃NaO₃S. When it binds to existing H⁺ and OH^- ions in solution, which causes changes in the flow of electrons, and thus it affects the amount of light absorbed. This colour change is visible through naked eye as a colour change in the solution.