AP Chemistry Flashcards: Common Ion Effect

What this deck covers

This deck focuses on Common Ion Effect, 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: For $CaF_2(s)$, what happens to solubility when $NaF(aq)$ is added?

Answer: Solubility decreases (common ion $F^-$). Added fluoride shifts dissolution equilibrium left.

Flashcard 2: Which ion is the common ion when $\text{CH}_3\text{COOH}(aq)$ is mixed with $\text{CH}_3\text{COONa}(aq)$?

Answer: $\text{CH}_3\text{COO}^-$. Both solutions contain the acetate ion.

Flashcard 3: For $AgCl(s)$, what happens to solubility when $NaCl(aq)$ is added?

Answer: Solubility decreases (common ion $Cl^-$). Added chloride shifts dissolution equilibrium left.

Flashcard 4: In $\text{AgCl}(s) \rightleftharpoons \text{Ag}^+ + \text{Cl}^-$, what happens to $[\text{Ag}^+]$ when $[\text{Cl}^-]$ is increased?

Answer: $[\text{Ag}^+]$ decreases. To maintain constant $K_{sp}$, $[\text{Ag}^+]$ must decrease.

Flashcard 5: Which ion is the common ion when $NH_4Cl$ is added to a solution containing $NH_3$?

Answer: $NH_4^+$. Both $NH_4Cl$ and protonated $NH_3$ contain ammonium ion.

Flashcard 6: What is the solubility-product expression for $\text{MX}(s) \rightleftharpoons \text{M}^+ + \text{X}^-$?

Answer: $K_{sp}=[\text{M}^+][\text{X}^-]$. Product of ion concentrations at equilibrium.

Flashcard 7: Assuming $[\text{F}^-]_{\text{initial}} \gg 2s$, what is $s$ for $\text{CaF}_2$ in $[\text{F}^-]$ using $K_{sp}$?

Answer: $s\approx\frac{K_{sp}}{[\text{F}^-]^2}$. When common ion dominates, solve $K_{sp}$ for cation concentration.

Flashcard 8: What is the solubility product expression for $MX(s)\rightleftharpoons M^+ + X^-$?

Answer: $K_{sp}=[M^+][X^-]$. Product of ion concentrations for 1:1 salt dissolution.

Flashcard 9: Identify the direction of shift when $NaOH$ is added to $NH_3(aq)$.

Answer: Shift left; $NH_3$ forms less $NH_4^+$. Added $OH^-$ shifts ammonia-water equilibrium left.

Flashcard 10: What happens to $pH$ when $A^-$ (the conjugate base) is added to a buffer of $HA/A^-$?

Answer: $pH$ increases. More conjugate base consumes $H^+$, raising pH.

Flashcard 11: Identify the direction of shift when $CH_3COONa$ is added to $CH_3COOH(aq)$.

Answer: Shift left; $CH_3COOH$ ionizes less. Added acetate ion suppresses acetic acid dissociation.

Flashcard 12: State the equilibrium expression for a weak base $B$ with $K_b$.

Answer: $K_b=\frac{[BH^+][OH^-]}{[B]}$. Products over reactants for weak base protonation equilibrium.

Flashcard 13: Which relationship is correct for a conjugate pair: $K_a$ and $K_b$ at $25^\circ C$?

Answer: $K_aK_b=K_w=1.0\times 10^{-14}$. Conjugate acid-base pairs multiply to water's ion product.

Flashcard 14: What is the net effect on $[\text{OH}^-]$ when $\text{BHCl}$ is added to a solution of weak base $\text{B}$?

Answer: $[\text{OH}^-]$ decreases. Added $\text{BH}^+$ shifts equilibrium left, reducing base ionization.

Flashcard 15: Identify the common ion when $\text{CaF}_2(s)$ is placed in a solution of $\text{NaF}(aq)$.

Answer: $\text{F}^-$. Fluoride ion is present in both the solid and added salt.

Flashcard 16: Which ion is the common ion when $NaF$ is added to a solution containing $HF$?

Answer: $F^-$. Both $NaF$ and $HF$ contain fluoride ion in solution.

Flashcard 17: What is the net ionic equation for common-ion suppression of $HA$ by adding $A^-$?

Answer: $HA(aq)\rightleftharpoons H^+(aq)+A^-(aq)$ shifts left. Added $A^-$ drives equilibrium toward undissociated $HA$.

Flashcard 18: State the equilibrium expression for a weak acid $HA$ with $K_a$.

Answer: $K_a=\frac{[H^+][A^-]}{[HA]}$. Products over reactants for weak acid dissociation equilibrium.

Flashcard 19: What is the buffer relationship between conjugate pairs: $\text{HA}$ and $\text{A}^-$, in terms of the common-ion effect?

Answer: $\text{A}^-$ suppresses ionization of $\text{HA}$. Conjugate base reduces conjugate acid ionization.

Flashcard 20: What is the net ionic equation for common-ion suppression of $B$ by adding $BH^+$?

Answer: $B(aq)+H_2O(l)\rightleftharpoons BH^+(aq)+OH^-(aq)$ shifts left. Added $BH^+$ drives equilibrium toward unprotonated $B$.

Flashcard 21: Which ion is the common ion when $\text{NH}_3(aq)$ is mixed with $\text{NH}_4\text{Cl}(aq)$?

Answer: $\text{NH}_4^+$. Both solutions contain the conjugate acid of ammonia.

Flashcard 22: What happens to $[OH^-]$ when a strong base is added to a weak base solution?

Answer: $[OH^-]$ increases; weak base ionization decreases. Strong base fully dissociates, suppressing weak base's partial ionization.

Flashcard 23: What is the molar solubility $s$ of $\text{AgCl}$ in pure water in terms of $K_{sp}$?

Answer: $s=\sqrt{K_{sp}}$. For 1:1 salt, $K_{sp}=s^2$ where $s$ is molar solubility.

Flashcard 24: Identify the common ion when $\text{BaSO}_4(s)$ is placed in a solution of $\text{Na}_2\text{SO}_4(aq)$.

Answer: $\text{SO}_4^{2-}$. Sulfate ion is present in both the solid and added salt.

Flashcard 25: What is the equilibrium expression for a weak acid $\text{HA}$: $\text{HA} \rightleftharpoons \text{H}^+ + \text{A}^-$?

Answer: $K_a=\frac{[\text{H}^+][\text{A}^-]}{[\text{HA}]}$. Products over reactants for weak acid dissociation.

Flashcard 26: What happens to $[H^+]$ when a strong acid is added to a weak acid solution?

Answer: $[H^+]$ increases; weak acid ionization decreases. Strong acid fully dissociates, suppressing weak acid's partial ionization.

Flashcard 27: What is the net effect on $[\text{H}^+]$ when $\text{NaA}$ is added to a solution of weak acid $\text{HA}$?

Answer: $[\text{H}^+]$ decreases. Added $\text{A}^-$ shifts equilibrium left, reducing acid dissociation.

Flashcard 28: Which direction does $\text{HA} \rightleftharpoons \text{H}^+ + \text{A}^-$ shift when $[\text{A}^-]$ is increased?

Answer: Left (toward $\text{HA}$). Excess product drives equilibrium toward reactants.

Flashcard 29: What is the effect on molar solubility when a common ion is added to a sparingly soluble salt?

Answer: Molar solubility decreases. Common ion shifts dissolution equilibrium left, reducing dissolved ions.

Flashcard 30: What happens to the molar solubility of $\text{AgCl}(s)$ when $\text{Cl}^-$ is added from $\text{NaCl}$?

Answer: Molar solubility decreases. Common ion shifts dissolution equilibrium left.

Flashcard 31: What is the equilibrium expression for a weak base $\text{B}$: $\text{B}+\text{H}_2\text{O} \rightleftharpoons \text{BH}^+ + \text{OH}^-$?

Answer: $K_b=\frac{[\text{BH}^+][\text{OH}^-]}{[\text{B}]}$. Products over reactants for weak base protonation.

Flashcard 32: What is the common-ion effect in aqueous equilibrium systems?

Answer: Added common ion shifts equilibrium left, reducing dissociation/solubility. Excess product ions drive equilibrium backward per Le Châtelier's principle.

Flashcard 33: What is the molar solubility $s$ of $\text{CaF}_2$ in pure water in terms of $K_{sp}$?

Answer: $s=\left(\frac{K_{sp}}{4}\right)^{\frac{1}{3}}$. For 1:2 salt, $K_{sp}=s(2s)^2=4s^3$.

Flashcard 34: Which direction does $\text{B}+\text{H}_2\text{O} \rightleftharpoons \text{BH}^+ + \text{OH}^-$ shift when $[\text{BH}^+]$ is increased?

Answer: Left (toward $\text{B}$). Excess product drives equilibrium toward reactants.

Flashcard 35: Assuming $[\text{Cl}^-]_{\text{initial}} \gg s$, what is $s$ for $\text{AgCl}$ in $[\text{Cl}^-]$ using $K_{sp}$?

Answer: $s\approx\frac{K_{sp}}{[\text{Cl}^-]}$. When common ion dominates, solve $K_{sp}$ for remaining ion.

Flashcard 36: What is the common-ion effect in aqueous equilibrium systems?

Answer: Adding a shared ion shifts equilibrium left, reducing ionization/solubility. Le Châtelier's principle: system responds to minimize disturbance.

Flashcard 37: What is the solubility product expression for $M(OH)_2(s)\rightleftharpoons M^{2+}+2OH^-$?

Answer: $K_{sp}=[M^{2+}][OH^-]^2$. Includes squared $[OH^-]$ due to stoichiometry coefficient of 2.