Chapter 15, Problem 92QRT

(a)

Interpretation Introduction

Interpretation:

The $\text{pH}$ of the solution of $\text{HF}$ with $0.050\text{M}$ molarity has to be calculated.

Concept Introduction:

According to Arrhenius's theory, “an acid is defined as a species which donates a proton”.  The weak acid that dissociates partially $\left(\sim 1\%\right)$ in water and the strong acid dissociates completely $\left(\sim 100\%\right)$ in water.  Acid releases proton in water.  The number of ${\text{H}}^{+}$ ions produced by a weak acid is less than that produced by a strong acid of the same molarity.

(b)

Interpretation Introduction

Interpretation:

The $\text{pH}$ of the solution formed by $1.58\text{g}$ $\text{NaF}$ and $250\text{mL}$ of $0.050\text{M}$ $\text{HF}$ has to be calculated.

Concept Introduction:

The buffer is a solution that resists any change in pH on addition of ${\text{H}}^{+}$ and ${\text{OH}}^{-}$.  An acidic buffer is made up of a weak acid and its salt.  A basic buffer is made up of a weak base and its salt.  The formula to calculate the $\text{pH}$ of the buffer is shown below.

  $\text{pH}=\text{p}{K}_{\text{a}}+\log \frac{\left[{\text{A}}^{-}\right]}{\left[\text{HA}\right]}$