An acid-base indicator has a dissociation constant . The acid form of the indicator is red and the b — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

The dissociation of the indicator is $HIn \rightleftharpoons H^+ + In^-$. The pH is given by the Henderson-Hasselbalch equation: $pH = pK_{In} + \log\frac{[In^-]}{[HIn]}$. For 80% red (acid form), $pH_1 = 5 + \log(20/80) = 5 - 0.60 = 4.40$. For 80% blue (basic form), $pH_2 = 5 + \log(80/20) = 5 + 0.60 = 5.60$. The required pH change is $\Delta pH = 5.60 - 4.40 = 1.20$.