Determine the pH of the following buffer solutions. (a) 20.0 mL of 0.050 M HCN(a q) is mixed wit

step 1 To calculate the pH of a solution that contains sodium cyanide and hydrocyanic acid, we simply n

Determine the pH of the following buffer solutions. (a) 20.0...

Determine the pH of the following buffer solutions. (a) $20.0 \mathrm{mL}$ of $0.050 \mathrm{M} \mathrm{HCN}(a q)$ is mixed with $80.0 \mathrm{mL}$ of $0.030 \mathrm{M} \mathrm{NaCN}(a q),$ where the $\mathrm{p} K_{\mathrm{a}}$ of HCN is equal to 9.31. (b) $40.0 \mathrm{mL}$ of $0.30 \mathrm{MPIPES}$ acid is reacted with $60.0 \mathrm{mL}$ of $0.15 \mathrm{MPIPES}$ base.

Determine the pH of the following buffer solutions.
(a) $20.0 \mathrm{mL}$ of $0.050 \mathrm{M} \mathrm{HCN}(a q)$ is mixed with $80.0 \mathrm{mL}$ of $0.030 \mathrm{M} \mathrm{NaCN}(a q),$ where the $\mathrm{p} K_{\mathrm{a}}$ of
HCN is equal to 9.31.
(b) $40.0 \mathrm{mL}$ of $0.30 \mathrm{MPIPES}$ acid is reacted with $60.0 \mathrm{mL}$ of $0.15 \mathrm{MPIPES}$ base.

Key Concepts

Stoichiometric Calculations

Stoichiometric calculations are crucial when preparing buffer solutions because they involve determining the actual number of moles of the acid and conjugate base present after mixing different solutions. These calculations account for the initial concentrations and volumes, enabling precise determination of the ratio required for applying the Henderson-Hasselbalch equation.

Buffer Solutions

A buffer solution is a mixture that resists significant changes in its pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base, or a weak base and its conjugate acid, working together to neutralize any added acids or bases while maintaining a relatively constant pH.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a formula used to estimate the pH of a buffer solution. It relates the pH of the solution to the pKa (acid dissociation constant) of the weak acid and the logarithm of the ratio of the concentrations (or moles) of the conjugate base to the acid, making it a cornerstone for buffer pH calculations.

pKa and Acid-Base Equilibrium

The pKa value of a weak acid is a quantitative measure of its acid strength, indicating the pH at which the acid is half dissociated. In the context of buffer solutions, understanding the acid-base equilibrium, including the role of pKa, is fundamental for predicting how the acid and its conjugate base will interact to stabilize the pH.

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