Imagine that

Question

you needed to choose an indicator for the titration of a strong base (like NaOH) with a strong acid
(like HNO3). You have the indicators in Table 1 available. Which indicator would you choose? Why?

Indicator [HIn] [ In] pKa
Maryland Red- Red Blue 4.3
Terrapin Yellow -Red Yellow 7.4
Terpel Purple - Blue Red 10.5

I think terrapin yellow would be the best choice because the pH of the equivalance point in a titration of strong base with a strong acid would be pH 7.

Answer 1

I agree with you.
The equivalence point for a strong acid/strong base titration is 7.0; therefore you want an indicator with pKa of 7 +/- 1 or 6 as a low value and 8 has a high value. 7.4 is the only one within that range.