Question

Phenophthalein cannot be used as an indicator in nh4oh against HCl?​

Answer 1

Answer

The best indicator for titrating HCl

with NH4OH is –

Let us first understand the characteristics of indicators. Indicators are generally used to detect the end point of titration. They change color in response to the chemical change occurring. They are usually weak acid or bases but their conjugate base or acid forms have different color due to difference in the absorption spectra. There are many different indicators used for various acid base titrations.

Here, in the question HCl

which is a strong acid is titrated against NH4OH which is a weak base. The reaction between the two leads to formation of NH4Cl salt. The reaction involved is-

HCl+NH4OH→NH4Cl+H2O

Due to the hydrolysis of the salt, the pH lies in the acid range. pH at the end point lies between 6 to 4. The methyl orange is best suited for the purpose.

Explanation: