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: 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 2: 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 3: 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 4: 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 5: 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 6: How do you find $[OH^-]$ from $pOH$?

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

Flashcard 7: What is the Bronsted-Lowry definition of a base?

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

Flashcard 8: 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 9: 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 10: 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 11: 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 12: 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 13: 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 14: 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 15: 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 16: What is the effect of temperature on the value of $K_w$?

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

Flashcard 17: What is the conjugate base of the bicarbonate ion, $HCO_3^{-}$?

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

Flashcard 18: What is the conjugate acid of ammonia, NH₃?

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

Flashcard 19: 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 20: Identify the Lewis definition of an acid.

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

Flashcard 21: How does $pH$ change when a weak acid is diluted?

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

Flashcard 22: 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 23: How is $pK_b$ calculated from $K_b$?

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

Flashcard 24: 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 25: 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 26: How is $[H^+]$ calculated from $pH$?

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

Flashcard 27: 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 28: 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 29: 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 30: What does a $pH$ greater than $7$ indicate?

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

Flashcard 31: 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 32: State the formula for calculating $pH$ from $[H^+]$ concentration.

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

Flashcard 33: 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 34: What is the conjugate base of acetic acid, CH₃COOH?

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