Chapter 11, Problem 125CP

Interpretation Introduction

Interpretation:The value of $K_a$ for weak acid $\text{HA}$ present in hydrogen compartment is to be calculated.

Concept introduction:Cell potential expression can be evaluated by expression as follows:

  $E_{\text{cell}}^{°}=E_{\text{oxidation}}^{°}+E_{\text{reduction}}^{°}$

The expression to evaluate the $E_{\text{cell}}$ as per the Nernst equation is given as follows:

  $E_{\text{cell}}=E_{\text{cell}}^{°}-\frac{0.0592}{n}\log \frac{\left[P\right]}{\left[R\right]}$

Where,

• $E_{\text{cell}}$ denotesoverall cell potential.
• $E_{\text{cell}}^{°}$ denotes standard cell potential.
• $n$ is the number of moles of electrons transferred in the reaction.
• $\left[P\right]$ denotes concentration of product.
• $\left[R\right]$ denotes concentration of reactant.

The equation corresponding to the equilibrium constant $\left(K_{\text{A}}\right)$ of weak acid $\text{HA}$ is given as,

  $K_a=\frac{\left[{\text{H}}^{+}\right]\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$

Where,

• $\left[{\text{H}}^{+}\right]$ concentration of ${\text{H}}^{+}$ ions.
• $\left[{\text{A}}^{-}\right]$ represents concentration of ${\text{A}}^{-}$ ions.
• $\left[\text{HA}\right]$ represents concentration of $\text{HA}$ .