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Questions and Answers
What must the product of ion concentrations satisfy in a saturated solution?
What must the product of ion concentrations satisfy in a saturated solution?
In order to compare the solubilities of two salts using their Ksp values, what condition must be met?
In order to compare the solubilities of two salts using their Ksp values, what condition must be met?
If two salts have Ksp values 7.5 x 10-10 and 3.0 x 10-8 respectively, what can be inferred about their solubilities?
If two salts have Ksp values 7.5 x 10-10 and 3.0 x 10-8 respectively, what can be inferred about their solubilities?
Which of the following salts produces two ions when dissolved?
Which of the following salts produces two ions when dissolved?
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When comparing salts that dissolve to form different numbers of ions, what conclusion can be drawn about their Ksp values?
When comparing salts that dissolve to form different numbers of ions, what conclusion can be drawn about their Ksp values?
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Which of these salts has the lowest solubility based on its Ksp value of 1.1 x 10-73?
Which of these salts has the lowest solubility based on its Ksp value of 1.1 x 10-73?
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Why can't Ksp values be used directly to predict relative solubilities of different salts?
Why can't Ksp values be used directly to predict relative solubilities of different salts?
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What is the relationship between a solute’s molar solubility and Ksp?
What is the relationship between a solute’s molar solubility and Ksp?
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How does the solubility of Mg(OH)2 change in acidic versus basic solutions?
How does the solubility of Mg(OH)2 change in acidic versus basic solutions?
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What effect does adding NH4+ to a solution containing NH3 have on the precipitation of Mg(OH)2?
What effect does adding NH4+ to a solution containing NH3 have on the precipitation of Mg(OH)2?
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Why does the solubility of silver phosphate (Ag3PO4) increase in acidic solutions?
Why does the solubility of silver phosphate (Ag3PO4) increase in acidic solutions?
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How does the pH of a solution influence the solubility of salts containing basic anions?
How does the pH of a solution influence the solubility of salts containing basic anions?
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What is the solubility behavior of silver chloride (AgCl) in acidic solutions?
What is the solubility behavior of silver chloride (AgCl) in acidic solutions?
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What is the primary method used to separate ions in a solution when they can precipitate with the same reagent?
What is the primary method used to separate ions in a solution when they can precipitate with the same reagent?
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Which of the following anions is NOT considered an effective base, potentially increasing salt solubility in acidic solutions?
Which of the following anions is NOT considered an effective base, potentially increasing salt solubility in acidic solutions?
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Which of the following salts is expected to be more soluble in acidic solutions?
Which of the following salts is expected to be more soluble in acidic solutions?
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Which factor directly influences the solubility Product Constant (Ksp) for a salt in solution?
Which factor directly influences the solubility Product Constant (Ksp) for a salt in solution?
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The solubility product constant (Ksp) is best described as:
The solubility product constant (Ksp) is best described as:
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How do weak acids influence the solubility of salts containing their corresponding anions?
How do weak acids influence the solubility of salts containing their corresponding anions?
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In the dissolution of Mg(OH)2, what occurs when hydronium ions are added to the solution?
In the dissolution of Mg(OH)2, what occurs when hydronium ions are added to the solution?
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What is a key characteristic of common anions that are effective bases?
What is a key characteristic of common anions that are effective bases?
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Which statement best conveys the limitations of using Ksp for solubility predictions?
Which statement best conveys the limitations of using Ksp for solubility predictions?
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What is the expected outcome when a solution of AgNO3 is added slowly to a mixture containing CrO42- and Br- ions?
What is the expected outcome when a solution of AgNO3 is added slowly to a mixture containing CrO42- and Br- ions?
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What drives the dissolution of slightly soluble salts like Mg(OH)2 in acidic conditions?
What drives the dissolution of slightly soluble salts like Mg(OH)2 in acidic conditions?
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Study Notes
Solubility Equilibria
- Solubility equilibria describes the dynamic equilibrium between a solid solute and its dissolved ions in a solution.
- A saturated solution exists when the rates of dissolution and crystallization are equal.
- The concentration of a saturated solution is its solubility.
- Solubility varies with temperature.
- A solubility-temperature graph is a solubility curve.
- Most ionic substances' solubility increases with temperature.
- Exceptions include anions such as SO32-, SO42-, AsO43-, and PO43-.
- An unsaturated solution contains less solute than a saturated solution.
- A supersaturated solution contains more solute than a saturated solution. Supersaturated solutions are unstable and will precipitate.
Saturated Solutions
- The concentration of a saturated solution is called its solubility.
- Solubility varies with temperature.
- A solubility-temperature graph is called a solubility curve.
- Solubility for various salts is shown on graphs, each line representing a different substance.
Aqueous Solubility
- Aqueous solubility is the amount of solute that can dissolve in 100 g of water at a given temperature.
- Solubility can be expressed in various ways such as molarities, mass percentages, or grams of solute/100 g of water.
- Points on the solubility curve represent saturated solutions. Areas above the curve represent supersaturated solutions and below unsaturated solutions.
Solubility
- Generally, solubilities of ionic substances increase with increasing temperature.
- Compounds containing anions (SO32-, SO42-, AsO43-, and PO43-) are exceptions.
- Adding solute to a solvent, with less than the amount needed for saturation, can result in an unsaturated solution, which the additional solute will dissolve.
- A saturated solution can be prepared by dissolving the solute at a high temperature and then allowing it to cool slowly.
Supersaturated Solutions
- Usually, excess solute crystallizes from a solution, but occasionally all the excess solute may stay in solution.
- Supersaturated solutions are unstable.
- If crystals of solute are added, the excess solute crystallizes.
Le Châtelier's Principle
- A system at equilibrium subjected to a change will spontaneously shift to counteract the change.
- Adding a product causes the equilibrium to shift to the left (reactants).
- Adding a reactant causes the equilibrium to shift to the right (products).
The Solubility Product Constant, Ksp
- The equilibrium constant for the reaction in which a solid salt dissolves to yield its constituent ions in solution.
- The concentration of the solid is omitted from the equilibrium constant expression because it is in its standard state.
- Example: CaSO4 (s) ⇌ Ca2+(aq) + SO42-(aq).
- Ksp = [Ca2+] [SO42-]
- Ksp = 9.1 × 10−6 (at 25°C)
Solubility vs. Solubility Product
- Solubility is an equilibrium position for a solution; a specific solubility value for a salt at particular temperatures.
- The solubility product, Ksp, is a constant value for a specific salt, at any specific temperature. The solubility product depends on ion activities.
The Relationship Between Solubility and Ksp
- There's a relationship between the solubility product constant (Ksp) and the molar solubility of a solute.
- Molar solubility is a solute's molarity in a saturated aqueous solution.
Relative Solubilities
- Compare Ksp values only for salts that have the same number of ions (e.g., AgCl, Cul).
- The larger the Ksp value, the more soluble the salt.
Fractional Precipitation
- Fractional precipitation is a technique used to separate two or more ions that can be precipitated by the same reagent.
- The rate of reagent addition is controlled to selectively precipitate different ions in a solution.
- The slower the reagent addition, the greater the chance the less soluble of the two products will precipitate first.
Solubility and pH
- The pH of a solution can greatly affect the solubility of a salt.
- This is especially true for salts whose anions are the conjugate bases of weak acids or the base OH⁻ itself.
- An example is Mg(OH)2, which is highly insoluble in water and is a common antacid commonly known as milk of magnesia.
- Hydroxide ions from magnesium hydroxide react with hydronium ions from stomach acid to form water.
- Increasing acidity increases the solubility of salts containing basic anions.
Incomplete Dissociation of Solute into Ions
- In solubility calculations, assume complete dissociation into ions, but this is often not a valid assumption.
- Solute might not be 100% ionic and some may dissolve as molecules or as ion pairs.
Simultaneous Equilibria
- The reversible reaction between a solid solute and its ions in solution, is never the only process.
- Other simultaneous processes occurring include water autoionization and reactions occurring between solute ions and other solution species. These may include acid-base reactions and complex ion formation.
Limitations of Ksp
- Ksp values are often limited to slightly soluble or essentially insoluble solutes.
- When calculating Ksp it is important to consider if other equilibria are occurring simultaneously
- Experimental solubility values can differ from calculated Ksp values, as the calculated ones are based on assuming complete dissociation.
- Molarities are often used in place of activities to simplify calculations.
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