Chapter 11, Problem 11.39P

Interpretation Introduction

Interpretation:

Chemical formula of  compound with negative $p{K}_a$ has to be written.

Concept Introduction:

Strong acids completely dissociates into ions in solvent.  This process releases proton and the solution is termed acidic.  Conversely the weak acids don’t dissociate completely into individual ions in solution.  Thus the solution of weak acid has both dissociated and non-dissociated forms of the acid existing in equilibrium.  The dissociation constant of weak acids is represented by $K_a.$

The $K_a$ value actually measures the strength of the acid – how readily it could release a proton or how readily a substance exhibit its acidic behavior.  The weak acids have lower $K_a$ value indicating that they don’t lose proton easily that they are not completely dissociated.  But indicating the acidic strength of weak acids merely by $K_a$ is not appropriate and applicable all the time that the value corresponding to the negative logarithm of $K_a$ value is considered as the expression for the acidity of weak acids.  Mathematically we could write,

$p{K}_a={\text{ - log}}_{10}{\text{K}}_a$

$K_a{\text{ and pK}}_a$ values are inversely proportional to each other.  Weaker acids having lower $K_a$ value have higher $p{K}_a$ value.  Stronger acids having higher $K_a$ value will have lower $p{K}_a$ value.