Question

For molecules with multiple ionizable groups, such as glycine, which of the following statements is true?1. At a pH near the pI, nearly all the molecules carry a net positive charge.2. At pH near the pI, nearly all the molecules carry no net charge.3. At a pH near the pI, nearly all the molecules carry a net negative charge.4. When the pH is near the pI, the solution is near its

Answer 1

2. At pH near the pI, nearly all the molecules carry no net charge

Step-by-step explanation:

The general equilibrium for a molecule with multiple ionizable groups could be:

H₃A⁺ ⇄ H₂A + H⁺ ⇄HA⁻ + H⁺⇄A²⁻ + H⁺

Where each equilibrium has its own pKa

The equilibriums in which H₂A are involved (The neutral molecule), are used to determine the isoelectrical point.

The isoelectrical point is defined as the value of pH in which the molecule has no net charge.

Thus, true option is:

2. At pH near the pI, nearly all the molecules carry no net charge