CFR14 Solubility Equilibria
Page 1: Introduction to CFR
Title: Cardiovascular System, Biological Fluids, Renal Function (CFR)
Focus: Understanding solubility equilibria in biological systems.
Page 2: Chemical Equilibrium
Definition of Equilibrium:
Reactants convert to products and vice versa.
The rate of forward reaction equals the rate of reverse reaction.
Dynamics at Equilibrium:
Both reactions (forward and reverse) are continuously occurring.
Concentrations of reactants and products remain constant over time.
Page 3: Equilibrium Constant
Example Reaction:
2 NH3(g) ⇌ N2(g) + 3 H2(g)
Equilibrium constant expression (K):
K = [N2][H2]^3 / [NH3]^2
Characteristics:
Concentrations of each species raised to the power of their stoichiometric coefficients.
K is unit-less and varies with reaction and temperature.
Page 4: Equilibrium Constant Expressions
Role of Solids:
Solids do not contribute to K since their concentrations are constant (fixed by density).
Example
Reaction: Fe(s) + 5 CO(g) ⇌ Fe(CO)5(g)
K = [Fe(CO)5] / [Fe][(CO)]^5
Important Note:
Only concentrations of gaseous or aqueous species are included in the equilibrium expression.
Page 5: Equilibrium Constant for liquids
Pure Liquids:
Concentration of pure liquids does not change and can be omitted from K.
Example: CH3CO2H(aq) + H2O(l) ⇌ CH3COO-(aq) + H3O+(aq)
K = [CH3CO2-][H3O+] / [CH3CO2H]
Page 6: Relationship Between K and Reaction Direction
Forward and Reverse Reactions Relation:
For the reaction 2 SO2(g) + O2(g) ⇌ 2 SO3(g):
K_forward = [SO3]^2 / [SO2]^2[O2]
K_reverse = [SO2]^2[O2] / [SO3]^2
K_forward and K_reverse are reciprocals of each other.
Page 7: Interpreting Equilibrium Constant
Situations:
K >> 1 indicates more products at equilibrium (favoring products).
K << 1 indicates more reactants at equilibrium (favoring reactants).
Examples:
For CH3CO2H + H2O ⇌ CH3COO- + H3O+, K = 1.8 x 10^-5.
For 2 H2 + O2 ⇌ 2 H2O, K = 3.5 x 10^81.
Page 8: Equilibrium Constant Recap
NH3(g) ⇌ N2(g) + 3 H2(g):
K determination involves raising concentrations to stoichiometric coefficients.
K is specific to the reaction and temperature, unit-less.
Page 9: Solids and K Definition
Solid Phase Contributions:
Not included in the equilibrium constant calculations.
Example: For the reaction, K remains dependent only on reactants and products in solution.
Page 10: Le Chatelier’s Principle
Definition:
A system at equilibrium will shift to minimize the effects of a stress applied to it.
Types of stress:
Change in concentration of reactants or products.
Change in pressure or volume in a gaseous system.
Change in temperature.
Page 11: Effect of Concentration Changes
Reaction: A + B ⇌ C + D
Changes to Consider:
Increase in [A] or [B]: shifts equilibrium to the right (towards products).
Decrease in [A] or [B]: shifts equilibrium to the left (towards reactants).
Increase in [C] or [D]: shifts equilibrium to the left.
Decrease in [C] or [D]: shifts equilibrium to the right.
Page 12: Learning Outcomes
Key Concepts to Understand:
Define the solubility product.
Calculate solubility product from molar solubility.
Understand common ion effects on solubility.
Analyze the impact of pH on solubility.
Recognize applications of the solubility product principle.
Page 13: Solubility Equilibria Phenomena
Example: Precipitation and Dissolution of calcium carbonate (CaCO3):
Process leads to formation of stalactites and stalagmites.
Interactions between Ca2+ and CO32- and their dynamics in dissolution or precipitation.
Page 14: Importance of Solubility
Biological Importance:
Key for absorption of nutrients and mineralization processes.
Significant for drug delivery and diagnostic processes.
Example Reaction: NaCl ⇌ Na+ + Cl-
Page 15: Dynamics in Saturated Solutions
Characteristics of Saturated Solutions:
Dynamic equilibrium exists between undissolved solids and dissolved ions.
Rate of dissolution equals rate of precipitation.
Ion concentrations remain constant.
Page 16: Dissolution of Ionic Solids
Consideration of Equilibrium with Initiation of Dissolution:
Example: CaF2 dissolving into Ca2+ and F-
The process increases ion concentrations and probability of collisions leading to precipitation.
Page 17: Reach Equilibrium in CaF2
Equilibrium Dynamics:
Forward and reverse reactions occur consistently without changing dissolved ion concentrations.
At equilibrium, the solution is saturated with no concentration change.
Page 18: Solubility Product Expression
Basic Formulation:
Ksp = [Ca2+][F-]^2 for CaF2 ⇌ Ca2+ + 2F-
Reflects relationship between solid form and its dissolved ions in saturated solutions.
Page 19: Ksp and Solid Concentration
Understanding absence of solids in Ksp calculations:
More solid increases surface area leading to higher solubility and reforming ion precipitation.
Page 20: Solubility Product Example
Copper Arsenate Reaction:
Cu3(AsO4)2(s) ⇌ 3Cu2+(aq) + 2AsO43-(aq)
Ksp = [Cu2+]^3[AsO43-]^2.
Page 21: Ksp Characteristics
Unique Ksp Values:
Solubility product is constant for a given substance at a specific temperature.
Solubility may vary infinitely under different conditions (pH, common ions).
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Page 23: Molar Solubility Concept
Definition:
Number of moles of a substance that can dissolve in 1 liter of solution at saturation.
Expressed in mol/L and calculable from Ksp and stoichiometric coefficients.
Page 24: Calculating Ksp
Example Calculation with CaF2:
Molar solubility of CaF2 is 3.4 x 10^-4 mol/L.
Ksp = [Ca2+][F-]^2 = [3.4 x 10^-4][2 x 3.4 x 10^-4]^2 = 1.57 x 10^-10.
Page 25: Ksp and Molar Solubility Reliability
Comparison of Ksp and solubility in salts:
Ksp relates to solubility dependent on ionic counts produced:
Salt examples: AgI (Ksp = 1.5 x 10^-16), CuI (Ksp = 5.0 x 10^-12), CaSO4 (Ksp = 6.1 x 10^-5).
General trend: larger Ksp translates to larger molar solubility.
Page 26: Salts with Different Ion Counts
Reliability of Ksp Comparisons:
Ksp cannot directly compare solubility of salts yielding different numbers of ions:
Salts comparison: CuS (Ksp = 8.5 x 10^-45) shows less molar solubility than Bi2S3 (Ksp = 1.1 x 10^-72).
Page 27: Common Ions Influence
Impact of Common Ions on Solubility:
Analyzing Ag2CrO4 in two scenarios with and without common ions affects dissolution.
Le Chatelier’s principle applies to shifts in equilibrium based on common ions.
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Initial conditions tracked for salt dissolution and its equilibrium when in solutions containing common ions.
Page 29: Common Ion Effect Variations
Different scenarios in salt dissolution:
Comparison highlights reduced solubility when common ions present impacting equilibrium concentrations.
Page 30: pH Influence on Solubility
Example with Mg(OH)2:
pH changes influence solubility — Increased pH reduces solubility while decreased pH increases it.
Page 31: Solubility of Ag3PO4
pH interactions:
PO43- reacts with H+ ions; decreased pH increases solubility by decreasing PO43- concentration.
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Page 34: Applications of Solubility
The importance of modifying solubility in drug development and dental health.
Page 35: Low Molar Solubility Use
Clinical Importance of Low Solubility:
Example: Barium sulfate as a radio contrast agent due to its low solubility and toxicity management.
Page 36: Tooth Decay Mechanism
Impact of low pH on tooth enamel:
Hydroxyapatite dissolution leads to cavities; remineralization occurs but is slower under acidic conditions.
Page 37: Fluoridation Benefits
Calcium fluoride enhances remineralization of enamel, creating less soluble fluorapatite, thereby reducing tooth decay.
Page 38: Drug Solubility Alterations
Drug formation through salt modes increases solubility; effects differ by counter ions as well.
Page 39: Salt Form and Solubility
The types of counter ions impact solubility of drugs, specifically in formulations for oral consumption.
Page 40: Doxycycline Common Ion Impact
Doxycycline’s solubility adjustments in acidic versus basic environments highlight its specific ion response behavior.
Page 41: Calculating Molar Solubility of PbI2
Example Calculation Summary:
Ksp = 7.1 x 10^-9; determination from dissociation equations leads to molar solubility outcome.
Page 42: Learning Outcomes Repeat
Reiteration of key concepts in solubility and product calculations details.
Page 43: Contact Information
For more information contact: Dr. Darren Griffith
Email: dgriffith@rcsi.com.