Question

An indicator is a weak acid and $pH$ range is $4.0$ to $6.0$. If the indicator is $50\text{\%}$ ionized in a given solution then what is the ionization constant of the acid?

• A. ${10}^{-4}$
• B. ${10}^{-5}$
• C. ${10}^{-6}$
• D. None of these

Answer 1

The correct option is B ${10}^{-5}$

As we know,
$pH$ range is $p{K}_{In}\pm 1$ and here, it is 4 to 6 means $5-1$ to $5+1$ so, $p{K}_{In}=5$ and $K_{In}={10}^{-5}$