Acid–Base Equilibria (5A) - MCAT Chemical and Physical Foundations of Biological Systems
Card 1 of 25
What is the Lewis definition of an acid?
What is the Lewis definition of an acid?
Tap to reveal answer
An electron pair acceptor. Lewis theory defines acids as species that accept electron pairs to form coordinate bonds.
An electron pair acceptor. Lewis theory defines acids as species that accept electron pairs to form coordinate bonds.
← Didn't Know|Knew It →
What is the Lewis definition of a base?
What is the Lewis definition of a base?
Tap to reveal answer
An electron pair donor. Lewis theory defines bases as species that donate electron pairs to form coordinate bonds.
An electron pair donor. Lewis theory defines bases as species that donate electron pairs to form coordinate bonds.
← Didn't Know|Knew It →
What is the conjugate base of the acid $\text{HA}$?
What is the conjugate base of the acid $\text{HA}$?
Tap to reveal answer
$\text{A}^-$. The conjugate base forms by removing a proton from the acid HA.
$\text{A}^-$. The conjugate base forms by removing a proton from the acid HA.
← Didn't Know|Knew It →
What is the conjugate acid of the base $\text{B}$?
What is the conjugate acid of the base $\text{B}$?
Tap to reveal answer
$\text{BH}^+$. The conjugate acid forms by adding a proton to the base B.
$\text{BH}^+$. The conjugate acid forms by adding a proton to the base B.
← Didn't Know|Knew It →
What is the relationship between $pK_a$ and $K_a$?
What is the relationship between $pK_a$ and $K_a$?
Tap to reveal answer
$pK_a=-\log(K_a)$. pKa is the negative logarithm of Ka, indicating acid strength inversely.
$pK_a=-\log(K_a)$. pKa is the negative logarithm of Ka, indicating acid strength inversely.
← Didn't Know|Knew It →
What is the Brønsted–Lowry definition of a base?
What is the Brønsted–Lowry definition of a base?
Tap to reveal answer
A proton ($\text{H}^+$) acceptor. Brønsted–Lowry theory defines bases as species that accept protons from acids.
A proton ($\text{H}^+$) acceptor. Brønsted–Lowry theory defines bases as species that accept protons from acids.
← Didn't Know|Knew It →
What is the formula for $K_a$ for $\text{HA} + \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{A}^-$?
What is the formula for $K_a$ for $\text{HA} + \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{A}^-$?
Tap to reveal answer
$K_a=\frac{[\text{H}_3\text{O}^+][\text{A}^-]}{[\text{HA}]}$. Ka expresses the equilibrium constant for weak acid dissociation, excluding water as a pure liquid.
$K_a=\frac{[\text{H}_3\text{O}^+][\text{A}^-]}{[\text{HA}]}$. Ka expresses the equilibrium constant for weak acid dissociation, excluding water as a pure liquid.
← Didn't Know|Knew It →
What is the relationship between conjugates: $pK_a(\text{HA})+pK_b(\text{A}^-)$ at $25,^{\circ}\text{C}$?
What is the relationship between conjugates: $pK_a(\text{HA})+pK_b(\text{A}^-)$ at $25,^{\circ}\text{C}$?
Tap to reveal answer
$pK_a+pK_b=14$. For conjugate pairs, pKa + pKb equals pKw = 14 at 25°C.
$pK_a+pK_b=14$. For conjugate pairs, pKa + pKb equals pKw = 14 at 25°C.
← Didn't Know|Knew It →
At $25,^{\circ}\text{C}$, what is $[\text{H}^+]$ in pure water?
At $25,^{\circ}\text{C}$, what is $[\text{H}^+]$ in pure water?
Tap to reveal answer
$[\text{H}^+]=1.0\times10^{-7},\text{M}$. In pure water at 25°C, [H+] = [OH-] from autoionization, yielding neutral pH 7.
$[\text{H}^+]=1.0\times10^{-7},\text{M}$. In pure water at 25°C, [H+] = [OH-] from autoionization, yielding neutral pH 7.
← Didn't Know|Knew It →
What is the formula for $K_b$ for $\text{B} + \text{H}_2\text{O} \rightleftharpoons \text{BH}^+ + \text{OH}^-$?
What is the formula for $K_b$ for $\text{B} + \text{H}_2\text{O} \rightleftharpoons \text{BH}^+ + \text{OH}^-$?
Tap to reveal answer
$K_b=\frac{[\text{BH}^+][\text{OH}^-]}{[\text{B}]}$. Kb expresses the equilibrium constant for weak base protonation, excluding water as a pure liquid.
$K_b=\frac{[\text{BH}^+][\text{OH}^-]}{[\text{B}]}$. Kb expresses the equilibrium constant for weak base protonation, excluding water as a pure liquid.
← Didn't Know|Knew It →
What is the relationship between $pK_b$ and $K_b$?
What is the relationship between $pK_b$ and $K_b$?
Tap to reveal answer
$pK_b=-\log(K_b)$. pKb is the negative logarithm of Kb, indicating base strength inversely.
$pK_b=-\log(K_b)$. pKb is the negative logarithm of Kb, indicating base strength inversely.
← Didn't Know|Knew It →
At $25,^{\circ}\text{C}$, what is the relationship between $pH$ and $pOH$?
At $25,^{\circ}\text{C}$, what is the relationship between $pH$ and $pOH$?
Tap to reveal answer
$pH+pOH=14$. At 25°C, pH + pOH equals pKw = 14 from water's ion product.
$pH+pOH=14$. At 25°C, pH + pOH equals pKw = 14 from water's ion product.
← Didn't Know|Knew It →
What is the value of $K_w$ at $25,^{\circ}\text{C}$?
What is the value of $K_w$ at $25,^{\circ}\text{C}$?
Tap to reveal answer
$K_w=1.0\times10^{-14}$. Kw is the ion product of water, constant at 25°C due to autoionization equilibrium.
$K_w=1.0\times10^{-14}$. Kw is the ion product of water, constant at 25°C due to autoionization equilibrium.
← Didn't Know|Knew It →
What is the relationship between $pH$ and $[\text{H}^+]$?
What is the relationship between $pH$ and $[\text{H}^+]$?
Tap to reveal answer
$pH=-\log([\text{H}^+])$. pH measures acidity as the negative logarithm of hydrogen ion concentration.
$pH=-\log([\text{H}^+])$. pH measures acidity as the negative logarithm of hydrogen ion concentration.
← Didn't Know|Knew It →
What is the Brønsted–Lowry definition of an acid?
What is the Brønsted–Lowry definition of an acid?
Tap to reveal answer
A proton ($\text{H}^+$) donor. Brønsted–Lowry theory defines acids as species that donate protons in reactions with bases.
A proton ($\text{H}^+$) donor. Brønsted–Lowry theory defines acids as species that donate protons in reactions with bases.
← Didn't Know|Knew It →
What is the relationship between conjugates: $K_a(\text{HA})K_b(\text{A}^-)$ at $25,^{\circ}\text{C}$?
What is the relationship between conjugates: $K_a(\text{HA})K_b(\text{A}^-)$ at $25,^{\circ}\text{C}$?
Tap to reveal answer
$K_aK_b=K_w$. For conjugate pairs, the product of Ka and Kb equals Kw at 25°C.
$K_aK_b=K_w$. For conjugate pairs, the product of Ka and Kb equals Kw at 25°C.
← Didn't Know|Knew It →
Which side is favored for $\text{HA}+\text{B}^-\rightleftharpoons \text{A}^-+\text{HB}$ when $pK_a(\text{HB})>pK_a(\text{HA})$?
Which side is favored for $\text{HA}+\text{B}^-\rightleftharpoons \text{A}^-+\text{HB}$ when $pK_a(\text{HB})>pK_a(\text{HA})$?
Tap to reveal answer
Products (equilibrium favors the weaker acid). When pKa(HB) > pKa(HA), HB is weaker, so equilibrium shifts to the weaker acid side.
Products (equilibrium favors the weaker acid). When pKa(HB) > pKa(HA), HB is weaker, so equilibrium shifts to the weaker acid side.
← Didn't Know|Knew It →
What is the Henderson–Hasselbalch equation for a buffer of $\text{HA}/\text{A}^-$?
What is the Henderson–Hasselbalch equation for a buffer of $\text{HA}/\text{A}^-$?
Tap to reveal answer
$pH=pK_a+\log!\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$. The equation relates buffer pH to pKa and the ratio of conjugate base to acid.
$pH=pK_a+\log!\left(\frac{[\text{A}^-]}{[\text{HA}]}\right)$. The equation relates buffer pH to pKa and the ratio of conjugate base to acid.
← Didn't Know|Knew It →
In a buffer, what is $pH$ when $[\text{A}^-]=[\text{HA}]$?
In a buffer, what is $pH$ when $[\text{A}^-]=[\text{HA}]$?
Tap to reveal answer
$pH=pK_a$. Equal concentrations give log(1) = 0, so pH equals pKa at half-equivalence.
$pH=pK_a$. Equal concentrations give log(1) = 0, so pH equals pKa at half-equivalence.
← Didn't Know|Knew It →
What is the relationship between $pOH$ and $[\text{OH}^-]$?
What is the relationship between $pOH$ and $[\text{OH}^-]$?
Tap to reveal answer
$pOH=-\log([\text{OH}^-])$. pOH measures basicity as the negative logarithm of hydroxide ion concentration.
$pOH=-\log([\text{OH}^-])$. pOH measures basicity as the negative logarithm of hydroxide ion concentration.
← Didn't Know|Knew It →
What is the approximate buffer range (in pH units) around $pK_a$ for effective buffering?
What is the approximate buffer range (in pH units) around $pK_a$ for effective buffering?
Tap to reveal answer
$pK_a\pm^1$. Effective buffering occurs when [A-]/[HA] is between 0.1 and 10, spanning pKa ±1.
$pK_a\pm^1$. Effective buffering occurs when [A-]/[HA] is between 0.1 and 10, spanning pKa ±1.
← Didn't Know|Knew It →
What is the formula for percent ionization of a weak acid $\text{HA}$ in terms of $[\text{H}^+]$ and $[\text{HA}]_0$?
What is the formula for percent ionization of a weak acid $\text{HA}$ in terms of $[\text{H}^+]$ and $[\text{HA}]_0$?
Tap to reveal answer
$%\text{ionization}=\frac{[\text{H}^+]}{[\text{HA}]_0}\times100%$. Percent ionization quantifies dissociation extent using equilibrium [H+] over initial [HA].
$%\text{ionization}=\frac{[\text{H}^+]}{[\text{HA}]_0}\times100%$. Percent ionization quantifies dissociation extent using equilibrium [H+] over initial [HA].
← Didn't Know|Knew It →
Identify the major species at $pH=pK_a+2$ for a monoprotic acid system $\text{HA}/\text{A}^-$.
Identify the major species at $pH=pK_a+2$ for a monoprotic acid system $\text{HA}/\text{A}^-$.
Tap to reveal answer
$\text{A}^-$ predominates. At pH = pKa + 2, [A-]/[HA] = 100, so the deprotonated form is major.
$\text{A}^-$ predominates. At pH = pKa + 2, [A-]/[HA] = 100, so the deprotonated form is major.
← Didn't Know|Knew It →
Identify the major species at $pH=pK_a-2$ for a monoprotic acid system $\text{HA}/\text{A}^-$.
Identify the major species at $pH=pK_a-2$ for a monoprotic acid system $\text{HA}/\text{A}^-$.
Tap to reveal answer
$\text{HA}$ predominates. At pH = pKa - 2, [A-]/[HA] = 0.01, so the protonated form is major.
$\text{HA}$ predominates. At pH = pKa - 2, [A-]/[HA] = 0.01, so the protonated form is major.
← Didn't Know|Knew It →
What is the net ionic equation for neutralization of a strong acid by a strong base in water?
What is the net ionic equation for neutralization of a strong acid by a strong base in water?
Tap to reveal answer
$\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}$. Strong acid-base neutralization produces water by complete reaction of H+ and OH- ions.
$\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}$. Strong acid-base neutralization produces water by complete reaction of H+ and OH- ions.
← Didn't Know|Knew It →