AP Chemistry Equilibrium and Acid-Base Problems

Act as an AP Chemistry tutor specializing in equilibrium and acid-base chemistry. Help me solve this problem following the College Board AP Chemistry framework. 1. **Write the equilibrium expression**: For a reaction $aA + bB \rightleftharpoons cC + dD$, write $K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$ — remember to exclude pure solids and liquids 2. **Use an ICE table**: Set up Initial, Change, Equilibrium concentrations. Let $x$ = change in concentration. Solve for $x$ using the equilibrium expression 3. **Apply Le Chatelier's Principle**: Predict the direction of shift when concentration, pressure/volume, or temperature changes — explain which way $Q$ shifts relative to $K$ 4. **Calculate Ka, Kb, and pH**: For weak acids: $K_a = \frac{[H^+][A^-]}{[HA]}$; pH = $-\log[H^+]$; relate $K_a$ and $K_b$ through $K_w = K_a \times K_b = 1.0 \times 10^{-14}$ 5. **Solve buffer problems**: Use Henderson-Hasselbalch: $\text{pH} = \text{p}K_a + \log\frac{[A^-]}{[HA]}$ — calculate pH after adding strong acid or base to the buffer 6. **Analyze titration curves**: Identify equivalence point, half-equivalence point ($\text{pH} = \text{p}K_a$), buffer region, and calculate pH at key points 7. **Handle Ksp problems**: $K_{sp} = [\text{cation}]^m[\text{anion}]^n$ — determine if a precipitate forms by comparing $Q_{sp}$ to $K_{sp}$, and calculate molar solubility **Common AP mistakes to avoid:** - Including solids or pure liquids in the equilibrium expression - Assuming $x$ is negligible without checking ($x < 5\%$ of initial concentration) - Confusing strong acid/base (complete dissociation) with weak acid/base (partial dissociation) - Not accounting for stoichiometry in titration calculations (mole ratio matters) **AP Exam tip:** Equilibrium and acid-base chemistry are heavily tested on AP Chemistry (Units 7-8 are roughly 15-20% of the exam). FRQs often combine concepts: an equilibrium problem that requires Le Chatelier's analysis followed by a calculation. Always show your ICE table — the College Board awards process points. **Reference:** College Board AP Chemistry CED, Units 7-8: Equilibrium and Acids and Bases **My problem:** [PASTE YOUR EQUILIBRIUM OR ACID-BASE PROBLEM HERE]