Question

The structure of aspartic acid is given below.

(A) The $p K_{ a _{1}}, p _{ a _{2}}$, and $p K_{ a _{3}}$ of $( A )$, respectively, are: $1.88,3.65$, and $9.60.p _{ a _{1}}$ corresponds to the ionisation of the $COOH$ group, of

$pK _{2}$ corresponds to the ionisation of $\left( NH _{3}\right)$ (ammonium ion). What is the $pH$ at isoelectric points (pI)?

• A. $\frac{ p K_{ a _{1}}+ p K_{ a _{2}}}{2}$
• B. $\frac{ p K_{ a _{1}}+ p K_{ a _{3}}}{2}$
• C. $\frac{ p K_{ a _{2}}+ p K_{ a _{3}}}{2}$
• D. $\frac{ p K_{ a _{1}}+ p K_{ a _{2}}+ p K_{ a _{3}}}{3}$

Answer 1

Answer: (A)

Correct answer is (a) $\frac{ p K_{ a _{1}}+ p K_{ a _{2}}}{2}$