Common-Ion Effect - AP Chemistry
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State the equilibrium expression for a weak acid $HA$ with $K_a$.
State the equilibrium expression for a weak acid $HA$ with $K_a$.
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$K_a=\frac{[H^+][A^-]}{[HA]}$. Products over reactants for weak acid dissociation equilibrium.
$K_a=\frac{[H^+][A^-]}{[HA]}$. Products over reactants for weak acid dissociation equilibrium.
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What happens to $[H^+]$ when a strong acid is added to a weak acid solution?
What happens to $[H^+]$ when a strong acid is added to a weak acid solution?
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$[H^+]$ increases; weak acid ionization decreases. Strong acid fully dissociates, suppressing weak acid's partial ionization.
$[H^+]$ increases; weak acid ionization decreases. Strong acid fully dissociates, suppressing weak acid's partial ionization.
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What is the common-ion effect in aqueous equilibrium systems?
What is the common-ion effect in aqueous equilibrium systems?
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Added common ion shifts equilibrium left, reducing dissociation/solubility. Excess product ions drive equilibrium backward per Le Châtelier's principle.
Added common ion shifts equilibrium left, reducing dissociation/solubility. Excess product ions drive equilibrium backward per Le Châtelier's principle.
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For $AgCl(s)$, what happens to solubility when $NaCl(aq)$ is added?
For $AgCl(s)$, what happens to solubility when $NaCl(aq)$ is added?
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Solubility decreases (common ion $Cl^-$). Added chloride shifts dissolution equilibrium left.
Solubility decreases (common ion $Cl^-$). Added chloride shifts dissolution equilibrium left.
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What happens to $pH$ when $A^-$ (the conjugate base) is added to a buffer of $HA/A^-$?
What happens to $pH$ when $A^-$ (the conjugate base) is added to a buffer of $HA/A^-$?
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$pH$ increases. More conjugate base consumes $H^+$, raising pH.
$pH$ increases. More conjugate base consumes $H^+$, raising pH.
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For $CaF_2(s)$, what happens to solubility when $NaF(aq)$ is added?
For $CaF_2(s)$, what happens to solubility when $NaF(aq)$ is added?
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Solubility decreases (common ion $F^-$). Added fluoride shifts dissolution equilibrium left.
Solubility decreases (common ion $F^-$). Added fluoride shifts dissolution equilibrium left.
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Identify the direction of shift when $NaOH$ is added to $NH_3(aq)$.
Identify the direction of shift when $NaOH$ is added to $NH_3(aq)$.
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Shift left; $NH_3$ forms less $NH_4^+$. Added $OH^-$ shifts ammonia-water equilibrium left.
Shift left; $NH_3$ forms less $NH_4^+$. Added $OH^-$ shifts ammonia-water equilibrium left.
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Identify the direction of shift when $CH_3COONa$ is added to $CH_3COOH(aq)$.
Identify the direction of shift when $CH_3COONa$ is added to $CH_3COOH(aq)$.
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Shift left; $CH_3COOH$ ionizes less. Added acetate ion suppresses acetic acid dissociation.
Shift left; $CH_3COOH$ ionizes less. Added acetate ion suppresses acetic acid dissociation.
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Which ion is the common ion when $NH_4Cl$ is added to a solution containing $NH_3$?
Which ion is the common ion when $NH_4Cl$ is added to a solution containing $NH_3$?
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$NH_4^+$. Both $NH_4Cl$ and protonated $NH_3$ contain ammonium ion.
$NH_4^+$. Both $NH_4Cl$ and protonated $NH_3$ contain ammonium ion.
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Which ion is the common ion when $NaF$ is added to a solution containing $HF$?
Which ion is the common ion when $NaF$ is added to a solution containing $HF$?
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$F^-$. Both $NaF$ and $HF$ contain fluoride ion in solution.
$F^-$. Both $NaF$ and $HF$ contain fluoride ion in solution.
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What is the effect on molar solubility when a common ion is added to a sparingly soluble salt?
What is the effect on molar solubility when a common ion is added to a sparingly soluble salt?
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Molar solubility decreases. Common ion shifts dissolution equilibrium left, reducing dissolved ions.
Molar solubility decreases. Common ion shifts dissolution equilibrium left, reducing dissolved ions.
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Which relationship is correct for a conjugate pair: $K_a$ and $K_b$ at $25^\circ C$?
Which relationship is correct for a conjugate pair: $K_a$ and $K_b$ at $25^\circ C$?
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$K_aK_b=K_w=1.0\times 10^{-14}$. Conjugate acid-base pairs multiply to water's ion product.
$K_aK_b=K_w=1.0\times 10^{-14}$. Conjugate acid-base pairs multiply to water's ion product.
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What is the solubility product expression for $M(OH)_2(s)\rightleftharpoons M^{2+}+2OH^-$?
What is the solubility product expression for $M(OH)_2(s)\rightleftharpoons M^{2+}+2OH^-$?
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$K_{sp}=[M^{2+}][OH^-]^2$. Includes squared $[OH^-]$ due to stoichiometry coefficient of 2.
$K_{sp}=[M^{2+}][OH^-]^2$. Includes squared $[OH^-]$ due to stoichiometry coefficient of 2.
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What is the solubility product expression for $MX(s)\rightleftharpoons M^+ + X^-$?
What is the solubility product expression for $MX(s)\rightleftharpoons M^+ + X^-$?
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$K_{sp}=[M^+][X^-]$. Product of ion concentrations for 1:1 salt dissolution.
$K_{sp}=[M^+][X^-]$. Product of ion concentrations for 1:1 salt dissolution.
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What is the net ionic equation for common-ion suppression of $B$ by adding $BH^+$?
What is the net ionic equation for common-ion suppression of $B$ by adding $BH^+$?
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$B(aq)+H_2O(l)\rightleftharpoons BH^+(aq)+OH^-(aq)$ shifts left. Added $BH^+$ drives equilibrium toward unprotonated $B$.
$B(aq)+H_2O(l)\rightleftharpoons BH^+(aq)+OH^-(aq)$ shifts left. Added $BH^+$ drives equilibrium toward unprotonated $B$.
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What is the net ionic equation for common-ion suppression of $HA$ by adding $A^-$?
What is the net ionic equation for common-ion suppression of $HA$ by adding $A^-$?
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$HA(aq)\rightleftharpoons H^+(aq)+A^-(aq)$ shifts left. Added $A^-$ drives equilibrium toward undissociated $HA$.
$HA(aq)\rightleftharpoons H^+(aq)+A^-(aq)$ shifts left. Added $A^-$ drives equilibrium toward undissociated $HA$.
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State the equilibrium expression for a weak base $B$ with $K_b$.
State the equilibrium expression for a weak base $B$ with $K_b$.
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$K_b=\frac{[BH^+][OH^-]}{[B]}$. Products over reactants for weak base protonation equilibrium.
$K_b=\frac{[BH^+][OH^-]}{[B]}$. Products over reactants for weak base protonation equilibrium.
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What happens to $[OH^-]$ when a strong base is added to a weak base solution?
What happens to $[OH^-]$ when a strong base is added to a weak base solution?
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$[OH^-]$ increases; weak base ionization decreases. Strong base fully dissociates, suppressing weak base's partial ionization.
$[OH^-]$ increases; weak base ionization decreases. Strong base fully dissociates, suppressing weak base's partial ionization.
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What is the equilibrium expression for a weak acid $\text{HA}$: $\text{HA} \rightleftharpoons \text{H}^+ + \text{A}^-$?
What is the equilibrium expression for a weak acid $\text{HA}$: $\text{HA} \rightleftharpoons \text{H}^+ + \text{A}^-$?
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$K_a=\frac{[\text{H}^+][\text{A}^-]}{[\text{HA}]}$. Products over reactants for weak acid dissociation.
$K_a=\frac{[\text{H}^+][\text{A}^-]}{[\text{HA}]}$. Products over reactants for weak acid dissociation.
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What is the common-ion effect in aqueous equilibrium systems?
What is the common-ion effect in aqueous equilibrium systems?
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Adding a shared ion shifts equilibrium left, reducing ionization/solubility. Le Châtelier's principle: system responds to minimize disturbance.
Adding a shared ion shifts equilibrium left, reducing ionization/solubility. Le Châtelier's principle: system responds to minimize disturbance.
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What is the molar solubility $s$ of $\text{CaF}2$ in pure water in terms of $K{sp}$?
What is the molar solubility $s$ of $\text{CaF}2$ in pure water in terms of $K{sp}$?
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$s=\left(\frac{K_{sp}}{4}\right)^{\frac{1}{3}}$. For 1:2 salt, $K_{sp}=s(2s)^2=4s^3$.
$s=\left(\frac{K_{sp}}{4}\right)^{\frac{1}{3}}$. For 1:2 salt, $K_{sp}=s(2s)^2=4s^3$.
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Assuming $[\text{F}^-]_{\text{initial}} \gg 2s$, what is $s$ for $\text{CaF}2$ in $[\text{F}^-]$ using $K{sp}$?
Assuming $[\text{F}^-]_{\text{initial}} \gg 2s$, what is $s$ for $\text{CaF}2$ in $[\text{F}^-]$ using $K{sp}$?
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$s\approx\frac{K_{sp}}{[\text{F}^-]^2}$. When common ion dominates, solve $K_{sp}$ for cation concentration.
$s\approx\frac{K_{sp}}{[\text{F}^-]^2}$. When common ion dominates, solve $K_{sp}$ for cation concentration.
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What is the molar solubility $s$ of $\text{AgCl}$ in pure water in terms of $K_{sp}$?
What is the molar solubility $s$ of $\text{AgCl}$ in pure water in terms of $K_{sp}$?
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$s=\sqrt{K_{sp}}$. For 1:1 salt, $K_{sp}=s^2$ where $s$ is molar solubility.
$s=\sqrt{K_{sp}}$. For 1:1 salt, $K_{sp}=s^2$ where $s$ is molar solubility.
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Which direction does $\text{B}+\text{H}_2\text{O} \rightleftharpoons \text{BH}^+ + \text{OH}^-$ shift when $[\text{BH}^+]$ is increased?
Which direction does $\text{B}+\text{H}_2\text{O} \rightleftharpoons \text{BH}^+ + \text{OH}^-$ shift when $[\text{BH}^+]$ is increased?
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Left (toward $\text{B}$). Excess product drives equilibrium toward reactants.
Left (toward $\text{B}$). Excess product drives equilibrium toward reactants.
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Assuming $[\text{Cl}^-]{\text{initial}} \gg s$, what is $s$ for $\text{AgCl}$ in $[\text{Cl}^-]$ using $K{sp}$?
Assuming $[\text{Cl}^-]{\text{initial}} \gg s$, what is $s$ for $\text{AgCl}$ in $[\text{Cl}^-]$ using $K{sp}$?
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$s\approx\frac{K_{sp}}{[\text{Cl}^-]}$. When common ion dominates, solve $K_{sp}$ for remaining ion.
$s\approx\frac{K_{sp}}{[\text{Cl}^-]}$. When common ion dominates, solve $K_{sp}$ for remaining ion.
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In $\text{AgCl}(s) \rightleftharpoons \text{Ag}^+ + \text{Cl}^-$, what happens to $[\text{Ag}^+]$ when $[\text{Cl}^-]$ is increased?
In $\text{AgCl}(s) \rightleftharpoons \text{Ag}^+ + \text{Cl}^-$, what happens to $[\text{Ag}^+]$ when $[\text{Cl}^-]$ is increased?
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$[\text{Ag}^+]$ decreases. To maintain constant $K_{sp}$, $[\text{Ag}^+]$ must decrease.
$[\text{Ag}^+]$ decreases. To maintain constant $K_{sp}$, $[\text{Ag}^+]$ must decrease.
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Which direction does $\text{HA} \rightleftharpoons \text{H}^+ + \text{A}^-$ shift when $[\text{A}^-]$ is increased?
Which direction does $\text{HA} \rightleftharpoons \text{H}^+ + \text{A}^-$ shift when $[\text{A}^-]$ is increased?
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Left (toward $\text{HA}$). Excess product drives equilibrium toward reactants.
Left (toward $\text{HA}$). Excess product drives equilibrium toward reactants.
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What is the buffer relationship between conjugate pairs: $\text{HA}$ and $\text{A}^-$, in terms of the common-ion effect?
What is the buffer relationship between conjugate pairs: $\text{HA}$ and $\text{A}^-$, in terms of the common-ion effect?
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$\text{A}^-$ suppresses ionization of $\text{HA}$. Conjugate base reduces conjugate acid ionization.
$\text{A}^-$ suppresses ionization of $\text{HA}$. Conjugate base reduces conjugate acid ionization.
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Identify the common ion when $\text{BaSO}_4(s)$ is placed in a solution of $\text{Na}_2\text{SO}_4(aq)$.
Identify the common ion when $\text{BaSO}_4(s)$ is placed in a solution of $\text{Na}_2\text{SO}_4(aq)$.
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$\text{SO}_4^{2-}$. Sulfate ion is present in both the solid and added salt.
$\text{SO}_4^{2-}$. Sulfate ion is present in both the solid and added salt.
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Identify the common ion when $\text{CaF}_2(s)$ is placed in a solution of $\text{NaF}(aq)$.
Identify the common ion when $\text{CaF}_2(s)$ is placed in a solution of $\text{NaF}(aq)$.
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$\text{F}^-$. Fluoride ion is present in both the solid and added salt.
$\text{F}^-$. Fluoride ion is present in both the solid and added salt.
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