Question

Version 1 12. Methyl red is a common acid-base indicator. It has a Ka equal to 6.3 x 10-. Its un-ionized form 7.82 is red and its anionic form is yellow. What color would a methyl red solution have at pH A) violet B) yellow C) green D) blue E) red 13 Assuming egual concentrations of conllgate hase and acid uhich one of tho f uolu, n a
How do you get the answer just a little confused

Answer 1

Ans:- B option i.e Yellow

Methyl red( C15H15N3O2) is a weak acid as well as a weak electrolyte , in water it is partially dissociated into its conjugate base i.e C15H14N3O2^- ( anion ) and H3O^+ or H^+ ion ( obtained from COOH gp of methyl red).

e.g C15H15N3O2 + H2O <----> C15H14N3O2^- + H3O^+

Now, at pH = 7.8 means slightly basic conditions , concentration of H3O^+ (product side) in equilibrium mixture decreases, because concentration of OH^- increases, therefore according to Le Chatelier's principle, equilibrium will shifts in forward(product side) direction and therefore yellow colour of anionic form of Methyl red starts appears.