Find the pH of each mixture of acids. a. 0.115 M in HBr and 0.125 M in HCHO2 b. 0.150 M in HNO2

step 1 To find the pH of these solutions that contain a mixture of acids, we need to focus on the stron

Find the pH of each mixture of acids. a. 0.115 M in HBr and...

Find the $\mathrm{pH}$ of each mixture of acids. a. 0.115 $\mathrm{M}$ in HBr and 0.125 $\mathrm{M}$ in $\mathrm{HCHO}_{2}$ b. 0.150 $\mathrm{M}$ in $\mathrm{HNO}_{2}$ and 0.085 $\mathrm{M}$ in $\mathrm{HNO}_{3}$ c. 0.185 $\mathrm{M}$ in $\mathrm{HCHO}_{2}$ and 0.225 $\mathrm{M}$ in $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}$ d. 0.050 $\mathrm{M}$ in acetic acid and 0.050 $\mathrm{M}$ in hydrocyanic acid

Find the $\mathrm{pH}$ of each mixture of acids.
a. 0.115 $\mathrm{M}$ in HBr and 0.125 $\mathrm{M}$ in $\mathrm{HCHO}_{2}$
b. 0.150 $\mathrm{M}$ in $\mathrm{HNO}_{2}$ and 0.085 $\mathrm{M}$ in $\mathrm{HNO}_{3}$
c. 0.185 $\mathrm{M}$ in $\mathrm{HCHO}_{2}$ and 0.225 $\mathrm{M}$ in $\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}$
d. 0.050 $\mathrm{M}$ in acetic acid and 0.050 $\mathrm{M}$ in hydrocyanic acid

Key Concepts

Acid Dissociation Constant (Ka)

The acid dissociation constant (Ka) is a measure of the strength of a weak acid and quantifies the extent to which an acid can donate protons in solution. It is central to setting up the equilibrium expression for weak acid dissociation, enabling the calculation of hydrogen ion concentration and thereby the pH.

pH Calculation

pH is determined by calculating the total concentration of hydrogen ions [H+] in solution, and then applying the formula pH = –log[H+]. In mixtures of acids, this involves summing up the contributions of hydrogen ions from each acid source, with careful consideration of whether the acids are strong (fully dissociating) or weak (partially dissociating).

Strong Acids

Strong acids completely ionize in water, meaning that their molar concentration directly equals the concentration of hydrogen ions they provide. This property allows for straightforward pH calculations, as the contribution from a strong acid is simply its concentration, unaffected by equilibrium considerations.

Weak Acids

Weak acids do not fully dissociate in solution. Their extent of ionization is governed by an equilibrium characterized by their acid dissociation constant (Ka). Computing the pH in the presence of a weak acid requires setting up and solving the equilibrium expression, which often involves approximations or quadratic solutions to determine the concentration of hydrogen ions.

Mixtures of Acids

When multiple acids are present, particularly a mix of strong and weak acids, the overall pH is primarily determined by the acid(s) that contribute the most to the hydrogen ion concentration. In mixtures with strong acids, their complete dissociation often dominates, while mixtures only containing weak acids require evaluating the contribution from each acid using their respective Ka values.

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