Ksp - Solubility Product Constant
The solubility product constant is a simplified equilibrium constant denoted as Ksp which is defined for equilibrium between a solid and its respective ions in a given solution. Its value shows the degree to which a compound can dissociate in water. The greater the solubility product constant, the more soluble is the compound. The Ksp expression for a given salt is the product of the concentrations of the ions.
Each concentration is raised to a power that is equal to the coefficient of that ion in a balanced equation to get the solubility equilibrium. The solubility product constants are used for describing the saturated solutions of ionic compounds of relatively low solubility. A saturated solution is in a dynamic equilibrium state between the dissolved and dissociated ionic compound and the undissolved solid. In this article, we will learn about what is the solubility product, what is Ksp, the solubility product definition, and some solubility product numerical.
Solubility Product Definition
The definition of the solubility product is given as follows:
Solubility is defined as the property of a substance known as solute to get dissolved in a solvent for the formation of a solution. The solubility of ionic compounds that dissociate and form cations and anions in water varies to a great extent. Some compounds are highly soluble and can even absorb moisture from the atmosphere whereas, on the other hand, the others are highly insoluble.
Solubility Product Constant
Now, let us understand in detail what is the solubility product constant.
The solubility product is a type of equilibrium constant whose value depends on temperature. Ksp usually increases with the increase in temperature because of the increased solubility.
Most ionic compounds which are insoluble would still dissolve in water to a small extent. These insoluble compounds are considered to be strong electrolytes since whatever portion of the compound is dissolved also dissociates. For example, silver chloride dissociates to a small extent in the silver ions and chloride ions when added to water.
\[AgCl (s) \leftrightarrow Ag^{+}(aq) + Cl^{-}(aq)\]
This process is written as an equilibrium since the dissociation occurs only to a smaller extent. Hence, an equilibrium expression is written for the process. You must keep in mind that the solid silver chloride does not have a variable concentration and is therefore not included in the expression. This is the solubility product principle.
\[K_{sp} =[Ag^{+}][cl^{-}] \]
Solubility Product Formula
The solubility product constant is used to describe the saturated solutions of ionic compounds having relatively low solubility. A saturated solution is said to be in a state of dynamic equilibrium between the ionic compound and the undissolved solid.
The Ksp formula is given in the form of the following equation:
\[M_{x}A_{y} (s) \rightarrow xM^{y+}(aq) + yA^{x-}(aq)\]
The general equilibrium constant is written as follows:
\[Kc = [M^{y+}]^{x} [A^{x-}]^{y} \]
Significance of the Solubility Product
The solubility depends on several parameters which include the lattice enthalpy of salt and solvation enthalpy of ions in the solution. These two factors are the most important. Let us learn about the significance of the solubility product in detail.
Whenever a salt is dissolved in a solvent, the strong forces of attraction of solute that are the lattice enthalpy of its ions need to be overcome by the interactions between the ions and the solvent.
The solvation enthalpy of ions is always negative and this means that energy is released during the process.
The nature of the solvent finds the amount of energy that is released during the solvation which is solvation enthalpy.
Non-polar solvents have a small value of solvation enthalpy which means that this energy is not sufficient for overcoming the lattice enthalpy.
Hence the salts are not dissolved in the non-polar solvents. Therefore, for a salt to be dissolved in a solvent, its solvation enthalpy must be greater than its lattice enthalpy.
The solubility depends on the temperature and it is varied for every salt.
Salts are Classified According to their Solubility which is Given in the Table Below:
Solubility Product Numericals
Let us now take a look at some of the Ksp chemistry examples.
Example 1:
Determine the solubility product constant for \[MgF_{2}\].
Solution:
The relevant equilibrium is given by:
\[MgF_{2} (s) \leftrightarrow Mg^{2+}(aq) + 2F^{-}(aq)\]
Hence, the associated equilibrium constant is given by:
\[K_{sp} =[Mg^{2+}][F^{2-}] \]
Example 2:
Give the solubility product constant for \[Ag_{2}CrO_{4}\].
Solution:
The relevant equilibrium is given by:
\[Ag_{2}CrO_{4} (s) \leftrightarrow 2Ag^{+}(aq) + CrO_{4}^{2-}(aq)\]
The associated equilibrium is therefore given by:
\[K_{sp} =[Ag^{2+}]^{2}[CrO_{4}^{2-}] \]
The Ksp-Solubility Relationship
Because it is basically the product of the solubilities of the ions in moles per liter, Ksp is called the solubility product. A salt's solubility product, or vice versa, can therefore be computed from its solubility.
The sensitivity of AgBr to light is used in photographic films. When light strikes an AgBr crystal, a small percentage of the Ag+ ions are reduced to silver metal. When the film is developed, the remaining Ag+ ions in these crystals are reduced to silver metal. To "fix" the image, AgBr crystals that do not absorb light are removed from the film.
Example: 3
To test if AgBr can be eradicated by merely washing the film, let's calculate the solubility of AgBr in water in grams per liter.
Solution:
We start with the equilibrium equation of this salt in an aqueous solution, which is a balanced equation.
AgBr(s) \[\Longleftrightarrow\] \[Ag^{+}(aq) + Br^{-}(aq) \]
The solubility product equation for this reaction is then written.
\[K_{sp} =[Ag^{+}][Br_{-}] = 5.0 \times 10^{-13}\]
For two unknowns, the Ag+ and Br- ion concentrations, one equation cannot be solved. However, by noting that one Ag+ ion is emitted for every Br- ion, we can derive a second equation. Because there is no alternative source of either ion in this solution, their equilibrium concentrations must be equal.
\[ [Ag^{+}]=[Br^{-}] \]
The following result is obtained by substituting this equation into the Ksp expression.
\[[Ag^{+}]^{2} = 5.0 \times 10^{-13} \]
The equilibrium concentrations of Ag+ and Br- ions can be determined by taking the square root of both sides of this equation.
\[ [Ag^{+}]=[Br^{-}]\] = \[7.1 \times 10^{-7} M \]
We can calculate the solubility in grams per liter after we know how many moles of AgBr dissolve in a liter of water.
\[ \frac{7.1 \times 10^{-7} \text{mol AgBr}}{1 L} \times \frac{187.8 g AgBr}{1 \text{mol AgBr}} = 1.3 \times 10^{-4} g \text{AgBr}/L\]
AgBr dissolves in water at a rate of 0.00013 grams per liter. Attempting to wash the unexposed AgBr off the photographic film with water is therefore impractical.
Calculating the solubility product for 1:1 salts like AgBr is relatively simple. We need to understand the relationship between a salt's solubility and the concentrations of its ions at equilibrium in order to expand such calculations to compounds with more complex formulas. The amount of salt that dissolves in water will be denoted by the symbol Cs.
Get to know more about the concepts of solubility product at Vedantu. The insights of the top subject matter experts will aid you to understand this topic better and use its concepts to solve problems in the exercises and exams.
FAQs on Solubility Product
1. Define Solubility Product
The solubility product is defined as the property that a substance shows in the solute for getting dissolved in a solvent in order for the formation of a solution. The solubility of the ionic compounds that disassociate and forms the cations and the anions in water varies to a greater extent. Some of the compounds are highly soluble and can absorb moisture from the atmosphere as well whereas, on the other hand, the other compounds are highly insoluble.
2. What Does Ksp Mean in Chemistry?
Ksp in chemistry means the solubility product constant. The solubility product is an equilibrium constant whose value depends on the temperature. Ksp generally increases whenever there is an increase in the temperature due to the increased solubility. Hence, the Ksp meaning in chemistry refers to the solubility product constant.
3. What is the Solubility product, Ksp?
When salts do not fully dissolve in a solvent, the solubility product, Ksp, is used. Water is commonly used as a solvent. The mathematical product of a substance's dissolved ion concentrations raised to the power of their stoichiometric coefficients is the solubility product. The equilibrium constant for a solid substance dissolving in an aqueous solution is the solubility product constant, Ksp. It denotes the concentration at which a substance dissolves in water. The greater the Ksp value of a material, the more soluble it is.
4. What is the significance of Solubility product?
Following are the significance of solubility product
A substance's solubility is determined by the size of its solubility product.
A heterogeneous equilibrium constant, or a specific form of the equilibrium constant, is the solubility product. It is relevant in saturated solutions where an ionic component has not completely dissolved.
Because solubility products change with temperature, the temperature at which they were measured must always be stated.
5. What is Ksp and What Does It Mean?
The solubility constant (Ksp) is also known as the solubility product. When a solid substance dissolves in a liquid/aqueous solution, the equilibrium constant is used in equations. To recall, a solute (what is being dissolved) is called soluble if it can dissolve more than 1 gram in 100 mL of water. Ksp is used to define solutes that are just slightly soluble in solution and do not entirely dissolve. Ksp is the amount of solute that will dissolve in solution.
6. What are the uses of Ksp?
Following are the uses of Ksp.
A substance's solubility is determined by the size of its solubility product.
When two solutions are mixed, the solubility product can be used to determine whether a precipitate will form.
Take the following equilibrium as an example:
\[PbCl_{2} \longleftrightarrow Pb^{2+} + 2Cl^{-} \]
The solubility product would be surpassed if the concentration of \[Cl^{-} \] was increased by adding HCl, and \[PbCl_{2}\] would precipitate from the solution until equilibrium was restored.
7. Where can I find notes on Solubility Product?
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