AP Chemistry Flashcards: Weak Acid And Base Equilibria

What this deck covers

This deck focuses on Weak Acid And Base Equilibria, giving you a quick way to review the definitions, rules, and examples that matter most for AP Chemistry.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Find $K_a$ given $pK_a = 4.76$.

Answer: $K_a = 1.74 \times 10^{-5}$. Use $K_a = 10^{-pK_a} = 10^{-4.76} = 1.74 \times 10^{-5}$.

Flashcard 2: What is the $pH$ of a neutral solution at $25^\text{o}$C?

Answer: $pH = 7$. Equal concentrations of $H^+$ and $OH^-$ at equilibrium.

Flashcard 3: Identify the relationship between $K_w$, $K_a$, and $K_b$ for conjugate acid-base pairs.

Answer: $K_w = K_a \times K_b$. For conjugate acid-base pairs, their equilibrium constants multiply to give $K_w$.

Flashcard 4: What is the expression for the equilibrium constant $K_b$ of a weak base?

Answer: $K_b = \frac{[\text{BH}^+][\text{OH}^-]}{[\text{B}]}$. Shows equilibrium between weak base and its protonation products.

Flashcard 5: How is $pK_b$ calculated from $K_b$?

Answer: $pK_b = -\text{log}(K_b)$. Negative logarithm converts base constant to pK scale.

Flashcard 6: What is the expression for the equilibrium constant $K_b$ of a weak base?

Answer: $K_b = \frac{[\text{BH}^+][\text{OH}^-]}{[\text{B}]}$. Shows equilibrium between weak base and its protonation products.

Flashcard 7: What does a smaller $K_b$ value indicate about the strength of a base?

Answer: The base is weaker. Lower $K_b$ means less dissociation and weaker base.

Flashcard 8: Determine the $pH$ of a solution if $[H^+] = 1 \times 10^{-3}$ M.

Answer: $pH = 3$. Use $pH = -\log(1 \times 10^{-3}) = 3$.

Flashcard 9: What does a larger $K_a$ value indicate about the strength of an acid?

Answer: The acid is stronger. Higher $K_a$ means greater dissociation and stronger acid.

Flashcard 10: How do you find $[OH^-]$ from $pOH$?

Answer: $[OH^-] = 10^{-pOH}$. Inverse logarithm converts pOH back to concentration.

Flashcard 11: What is the Bronsted-Lowry definition of a base?

Answer: A base is a proton acceptor. Accepts protons from acids in chemical reactions.

Flashcard 12: What is the general expression for the equilibrium constant $K_a$ of a weak acid?

Answer: $K_a = \frac{[\text{H}^+][\text{A}^-]}{[\text{HA}]}$. Shows equilibrium between weak acid and its dissociation products.

Flashcard 13: What is the $pH$ of a neutral solution at $25^\text{o}$C?

Answer: $pH = 7$. Equal concentrations of $H^+$ and $OH^-$ at equilibrium.

Flashcard 14: What is the expression for the percent ionization of a weak acid?

Answer: Percent ionization = \frac{[\text{H}^+]}{[\text{HA}]_0} \times 100\text{%}. Ratio of ionized acid to initial concentration times 100%.

Flashcard 15: What is the relationship between $pK_a$ and the strength of an acid?

Answer: Lower $pK_a$ means stronger acid. Lower $pK_a$ corresponds to larger $K_a$ and stronger acid.

Flashcard 16: What is the formula for the autoionization of water?

Answer: $2 \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{OH}^-$. Water molecules exchange protons to form ions.

Flashcard 17: What is the formula for the autoionization of water?

Answer: $2 \text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{OH}^-$. Water molecules exchange protons to form ions.

Flashcard 18: Calculate the $pH$ for $[OH^-] = 4 \times 10^{-5}$ M.

Answer: $pH = 9.6$. Find $pOH = 4.4$, then $pH = 14 - 4.4 = 9.6$.

Flashcard 19: Which is stronger: an acid with $K_a = 1.0 \times 10^{-4}$ or $K_a = 1.0 \times 10^{-6}$?

Answer: The acid with $K_a = 1.0 \times 10^{-4}$ is stronger. Larger $K_a$ value indicates greater acid dissociation.

Flashcard 20: What is the $pH$ of a $0.01$ M sulfuric acid solution assuming complete dissociation?

Answer: $pH = 2$. Diprotic acid: $[H^+] = 0.02$ M, so $pH = -\log(0.02) = 2$.

Flashcard 21: Identify the relationship between $K_w$, $K_a$, and $K_b$ for conjugate acid-base pairs.

Answer: $K_w = K_a \times K_b$. For conjugate acid-base pairs, their equilibrium constants multiply to give $K_w$.

Flashcard 22: Identify the Lewis definition of an acid.

Answer: An acid is an electron pair acceptor. Accepts electron pairs from Lewis bases.

Flashcard 23: Calculate the $pOH$ of a solution with $[OH^-] = 2 \times 10^{-3}$ M.

Answer: $pOH = 2.7$. Use $pOH = -\log(2 \times 10^{-3}) = 2.7$.

Flashcard 24: State the formula for calculating $pH$ from $[H^+]$ concentration.

Answer: $pH = -\text{log}([H^+])$. Negative logarithm converts concentration to pH scale.

Flashcard 25: How is $[H^+]$ calculated from $pH$?

Answer: $[H^+] = 10^{-pH}$. Inverse logarithm converts pH back to concentration.

Flashcard 26: What is the relationship between $pH$ and $pOH$ at $25^\text{o}$C?

Answer: $pH + pOH = 14$. Sum of pH and pOH equals 14 at standard temperature.

Flashcard 27: What is the value of $K_w$ at $25^\text{o}$C?

Answer: $K_w = 1.0 \times 10^{-14}$. Ion product of water at standard temperature.

Flashcard 28: How do you find $[OH^-]$ from $pOH$?

Answer: $[OH^-] = 10^{-pOH}$. Inverse logarithm converts pOH back to concentration.

Flashcard 29: What is the effect of temperature on the value of $K_w$?

Answer: $K_w$ increases with temperature. Higher temperature increases water dissociation.

Flashcard 30: What is the conjugate base of the bicarbonate ion, $HCO_3^{-}$?

Answer: $CO_3^{2-}$. Loses another proton to form carbonate ion.

Flashcard 31: What is the conjugate acid of ammonia, NH₃?

Answer: NH₄^+. Gains a proton to form the conjugate acid.

Flashcard 32: What is the expression for the percent ionization of a weak acid?

Answer: Percent ionization = $\frac{[\text{H}^+]}{[\text{HA}]_0} \times 100\%$. Ratio of ionized acid to initial concentration times 100%.

Flashcard 33: Which is stronger: an acid with $K_a = 1.0 \times 10^{-4}$ or $K_a = 1.0 \times 10^{-6}$?

Answer: The acid with $K_a = 1.0 \times 10^{-4}$ is stronger. Larger $K_a$ value indicates greater acid dissociation.

Flashcard 34: Find the $pK_a$ given $K_a = 1.8 \times 10^{-5}$.

Answer: $pK_a = 4.74$. Use $pK_a = -\log(K_a) = -\log(1.8 \times 10^{-5}) = 4.74$.

Flashcard 35: Identify the Lewis definition of an acid.

Answer: An acid is an electron pair acceptor. Accepts electron pairs from Lewis bases.

Flashcard 36: How does $pH$ change when a weak acid is diluted?

Answer: $pH$ increases slightly. Dilution reduces concentration but increases degree of ionization.

Flashcard 37: What is the relationship between $pH$ and $pOH$ at $25^\text{o}$C?

Answer: $pH + pOH = 14$. Sum of pH and pOH equals 14 at standard temperature.

Flashcard 38: Calculate the $pOH$ of a solution with $[OH^-] = 2 \times 10^{-3}$ M.

Answer: $pOH = 2.7$. Use $pOH = -\log(2 \times 10^{-3}) = 2.7$.

Flashcard 39: What is the $pH$ of a $0.01$ M sulfuric acid solution assuming complete dissociation?

Answer: $pH = 2$. Diprotic acid: $[H^+] = 0.02$ M, so $pH = -\log(0.02) = 2$.

Flashcard 40: How is $pK_b$ calculated from $K_b$?

Answer: $pK_b = -\text{log}(K_b)$. Negative logarithm converts base constant to pK scale.

Flashcard 41: Find $K_a$ given $pK_a = 4.76$.

Answer: $K_a = 1.74 \times 10^{-5}$. Use $K_a = 10^{-pK_a} = 10^{-4.76} = 1.74 \times 10^{-5}$.

Flashcard 42: Identify the effect of dilution on the $pH$ of a weak acid solution.

Answer: Dilution increases $pH$ slightly. Equilibrium shifts right, increasing ionization and pH.

Flashcard 43: What is the conjugate acid of ammonia, NH₃?

Answer: NH₄^+. Gains a proton to form the conjugate acid.

Flashcard 44: What is the Bronsted-Lowry definition of a base?

Answer: A base is a proton acceptor. Accepts protons from acids in chemical reactions.

Flashcard 45: How is $[H^+]$ calculated from $pH$?

Answer: $[H^+] = 10^{-pH}$. Inverse logarithm converts pH back to concentration.

Flashcard 46: Determine the $pH$ of a $0.1$ M NaOH solution.

Answer: $pH = 13$. Strong base: $[OH^-] = 0.1$ M, so $pOH = 1$, $pH = 13$.

Flashcard 47: How does $pH$ change when a weak acid is diluted?

Answer: $pH$ increases slightly. Dilution reduces concentration but increases degree of ionization.

Flashcard 48: What is the general expression for the equilibrium constant $K_a$ of a weak acid?

Answer: $K_a = \frac{[\mathrm{H}^{+}] [\mathrm{A}^{-}]}{[\text{HA}]}$. Shows equilibrium between weak acid and its dissociation products.

Flashcard 49: What is the $pH$ of a $0.05$ M hydrochloric acid solution?

Answer: $pH = 1.3$. Strong acid completely dissociates: $pH = -\log(0.05) = 1.3$.

Flashcard 50: What is the conjugate base of the bicarbonate ion, $HCO_3^{-}$?

Answer: $CO_3^{2-}$ $. Loses another proton to form carbonate ion.

Flashcard 51: Determine the $pK_b$ given $K_b = 4.5 \times 10^{-4}$.

Answer: $pK_b = 3.35$. Use $pK_b = -\log(4.5 \times 10^{-4}) = 3.35$.

Flashcard 52: What is the effect of temperature on the value of $K_w$?

Answer: $K_w$ increases with temperature. Higher temperature increases water dissociation.

Flashcard 53: What does a larger $K_a$ value indicate about the strength of an acid?

Answer: The acid is stronger. Higher $K_a$ means greater dissociation and stronger acid.

Flashcard 54: Identify the effect of dilution on the $pH$ of a weak acid solution.

Answer: Dilution increases $pH$ slightly. Equilibrium shifts right, increasing ionization and pH.

Flashcard 55: What does a smaller $K_b$ value indicate about the strength of a base?

Answer: The base is weaker. Lower $K_b$ means less dissociation and weaker base.

Flashcard 56: Determine the $pK_b$ given $K_b = 4.5 \times 10^{-4}$.

Answer: $pK_b = 3.35$. Use $pK_b = -\log(4.5 \times 10^{-4}) = 3.35$.

Flashcard 57: Find the $pK_a$ given $K_a = 1.8 \times 10^{-5}$.

Answer: $pK_a = 4.74$. Use $pK_a = -\log(K_a) = -\log(1.8 \times 10^{-5}) = 4.74$.

Flashcard 58: Determine the $pH$ of a $0.1$ M NaOH solution.

Answer: $pH = 13$. Strong base: $[OH^-] = 0.1$ M, so $pOH = 1$, $pH = 13$.

Flashcard 59: What is the $pH$ of a $0.05$ M hydrochloric acid solution?

Answer: $pH = 1.3$. Strong acid completely dissociates: $pH = -\log(0.05) = 1.3$.

Flashcard 60: What is the conjugate base of acetic acid, CH₃COOH?

Answer: CH₃COO⁻. Loses a proton to form the conjugate base.

Flashcard 61: What does a $pH$ greater than $7$ indicate?

Answer: The solution is basic. pH above 7 means hydroxide concentration exceeds hydronium.

Flashcard 62: Determine the $pH$ of a solution if $[H^+] = 1 \times 10^{-3}$ M.

Answer: $pH = 3$. Use $pH = -\log(1 \times 10^{-3}) = 3$.

Flashcard 63: State the formula for calculating $pH$ from $[H^+]$ concentration.

Answer: $pH = -\text{log}([H^+])$. Negative logarithm converts concentration to pH scale.

Flashcard 64: What does a $pH$ greater than $7$ indicate?

Answer: The solution is basic. pH above 7 means hydroxide concentration exceeds hydronium.

Flashcard 65: Calculate the $pH$ for $[OH^-] = 4 \times 10^{-5}$ M.

Answer: $pH = 9.6$. Find $pOH = 4.4$, then $pH = 14 - 4.4 = 9.6$.

Flashcard 66: What is the value of $K_w$ at $25^\text{o}$C?

Answer: $K_w = 1.0 \times 10^{-14}$. Ion product of water at standard temperature.

Flashcard 67: What is the relationship between $pK_a$ and the strength of an acid?

Answer: Lower $pK_a$ means stronger acid. Lower $pK_a$ corresponds to larger $K_a$ and stronger acid.

Flashcard 68: What is the conjugate base of acetic acid, CH₃COOH?

Answer: CH₃COO⁻. Loses a proton to form the conjugate base.