Calculate the pH of the following acid-base buffers a. 100 mL of 0.025 M formic acid and 0.015

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Calculate the pH of the following acid-base buffers a. 100...

Calculate the $\mathrm{pH}$ of the following acid-base buffers a. $100 \mathrm{~mL}$ of $0.025 \mathrm{M}$ formic acid and $0.015 \mathrm{M}$ sodium formate b. $50.00 \mathrm{~mL}^2 0.12 \mathrm{M} \mathrm{NH}_3$ and $3.50 \mathrm{~mL}$ of $1.0 \mathrm{M} \mathrm{HCl}$ c. $5.00 \mathrm{~g}$ of $\mathrm{Na}_2 \mathrm{CO}_3$ and $5.00 \mathrm{~g}$ of $\mathrm{NaHCO}_3$ in $0.100 \mathrm{~L}$

Calculate the $\mathrm{pH}$ of the following acid-base buffers
a. $100 \mathrm{~mL}$ of $0.025 \mathrm{M}$ formic acid and $0.015 \mathrm{M}$ sodium formate
b. $50.00 \mathrm{~mL}^2 0.12 \mathrm{M} \mathrm{NH}_3$ and $3.50 \mathrm{~mL}$ of $1.0 \mathrm{M} \mathrm{HCl}$
c. $5.00 \mathrm{~g}$ of $\mathrm{Na}_2 \mathrm{CO}_3$ and $5.00 \mathrm{~g}$ of $\mathrm{NaHCO}_3$ in $0.100 \mathrm{~L}$

Key Concepts

Calculation of pKa and pKb Values

The pKa and pKb values are measures of the strength of a weak acid and a weak base, respectively. These values are logarithmic representations of the acid dissociation constant (Ka) or the base dissociation constant (Kb). They are vital in buffer calculations as they are directly used in the Henderson–Hasselbalch equation to link the concentrations of the conjugate pair with the pH of the buffer system.

Acid-Base Reaction Stoichiometry

Acid-base reaction stoichiometry involves quantitatively analyzing the moles of acid and base present and how they react with each other. In buffer preparation, especially when a strong acid or base is added to a solution containing a weak base or acid, stoichiometric calculations are essential to determine the final concentrations of the buffering components, which then influence the pH of the resulting solution.

Conjugate Acid-Base Pairs

Conjugate acid-base pairs consist of two species that differ by one proton. In a buffer solution, the weak acid and its conjugate base (or the weak base and its conjugate acid) work together to moderate pH fluctuations. Understanding these pairs is fundamental to predicting how a solution will respond to the addition of an acid or a base, as the equilibrium between the pair is key to the buffer's function.

Henderson–Hasselbalch Equation

The Henderson–Hasselbalch equation provides a simplified way to calculate the pH of a buffer solution. It relates the pH to the pKa (or pKb) of the weak acid (or base) and the ratio of the concentrations of the conjugate base to the acid. This equation is especially useful because it allows for quick calculation of pH in buffer systems without solving equilibrium expressions in detail.

Buffer Solutions

Buffer solutions are mixtures of a weak acid and its conjugate base or a weak base and its conjugate acid that resist changes in pH when small amounts of strong acid or base are added. They work by neutralizing added acids or bases through the reversible reaction between the weak acid/base and its conjugate, thereby maintaining a relatively stable pH, which is crucial in many chemical and biological processes.

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