In a volumetric estimation of HCl, a suitable base is used to titrate the acid. The choice of base is important as it can affect the accuracy of the results. Phenolphthalein is a commonly used indicator in acid-base titrations as it changes color from colorless to pink at a pH of around 8.2.


The following bases are suitable for HCl titration with phenolphthalein indicator:

• Sodium hydroxide (NaOH)


• Potassium hydroxide (KOH)


• Rubidium hydroxide (RbOH)


• Ammonium hydroxide (NH4OH)

Out of the four bases mentioned above, ammonium hydroxide (NH4OH) is unsuitable for HCl titration with phenolphthalein indicator.


Ammonium hydroxide is a weak base and its dissociation in water is as follows:
NH4OH ⇌ NH4+ + OH-

In the titration of HCl with NH4OH, the following reaction takes place:
HCl + NH4OH → NH4Cl + H2O

However, since NH4OH is a weak base, its reaction with HCl will not be complete. This means that at the equivalence point, not all of the HCl will have reacted with NH4OH, and some of the HCl will remain unreacted. As a result, the pH of the solution will not be high enough to cause phenolphthalein to change color from colorless to pink. Therefore, the endpoint of the titration will not be accurately determined using phenolphthalein indicator.


In conclusion, ammonium hydroxide (NH4OH) is unsuitable for HCl titration with phenolphthalein indicator as it is a weak base and its reaction with HCl will not be complete. The other three bases mentioned above, namely sodium hydroxide (NaOH), potassium hydroxide (KOH), and rubidium hydroxide (RbOH) are suitable for HCl titration with phenolphthalein indicator.

Explanation:Hph work on strong base.

Phenolphthalein use as indicators .

It is pink colour in basic medium and colourless in acidic medium,

So , in this NaOH,KOH,RbOH are strong base

And NH4OH Is weak base and it is correct answer