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Introduction
There are various ways and means to determine the solubility of a salt. There are solubility rules that govern the solubility of various ionic compounds. You may already be familiar with them. However, if we apply those concepts, we can find if an ionic compound precipitates or dissolves.
To understand the concept of soluble salts, we need to apply the basics of chemical equilibria. This will result in an equilibrium constant and solubility constant. These two are the primary requirements for calculating the solubility of salts. All these make up the study material notes on soluble salts.
What is Solubility Equilibrium?
This is defined as the equilibrium established between the precipitate and the dissolved ions. The equilibrium is established only when:
Rate of dissolution = Rate of crystallisation
Now, you may wonder what does the solubility of a salt denote?
For instance, if one mole of sodium sulphate dissolves in water completely, then it means that: for every mole that dissolves in water, two sodium moles are formed alongside one mole of sulphate. Hence, the basics of solubility are used to determine the moles formed on complete saturation. The number of ions formed solely depends on the chemical formula of the ionic compound. It is an important factor in determining soluble salts.
What is a Solubility Product?
In simple words, the solubility product is defined as the number of moles of the solute that is dissolved entirely in a given amount of solvent.
Suppose we dive deeper into the concept of solubility products. In that case, we determine that: at a given temperature, the solubility product is the molar concentration of the given ions in a solution. These ions are raised to the power of the number of ions produced on the dissociation of only one electrolyte molecule.
It is a constant during the dissolution process. To express it:
What are the factors that Solubility Product is dependent upon?
Several parameters define the solubility product. The most important factors are:
- Lattice Enthalpy: The cohesive forces that are working together to maintain an ionic bond in solids.
- Hydration Enthalpy: This type of energy is released when a mole of ion goes through hydration.
It is said that solubility products are dependent on these two factors immensely. If the lattice enthalpy is low and the hydration enthalpy is high, we will observe that the salt dissolves easily.
Significance of Solubility Product
The solubility product has great significance in terms of a solution. Some of these are:
- The amount of energy released during the solvation determines the nature of the solvent. It is known as solvation enthalpy.
- The solvation enthalpy of non-polar solvents is minimal. This means that it is not enough to overcome the lattice enthalpy.
- It is known that a salt behaves like a soluble salt only when the solvation enthalpy is much greater than the lattice enthalpy. If that’s not the case, the salt is not dissolved. Hence, salts do not dissolve in nonpolar solutions.
- Ions have negative solvation energy since energy is always released during the reaction.
- When salt dissolves a solvent, the lattice enthalpy needs to be overcome by the interaction between the ions and the solvent.
Solubility and Common Ion Effect
To understand the concept of the common ion effect clearly, let’s consider a solution of weak electrolytes. In such a solution, there is the presence of an equilibrium interaction between the unionised molecules and the ions present in the solution.
For instance, AB here is a weak electrolyte,
AB ⇒A† + B‾
If there’s a solution in equilibrium that means that the solution and solute are in equilibrium. If we add a common ion, it results in a decrease of the solubility of the solute. If a strong electrolyte is added to the solution, the equilibrium is disturbed. It can easily dissociate into A+ or B-.
To establish the equilibrium back to the reaction, Le-Chatelier’s principle is applied. Following this principle, the whole process shifts towards the backward direction. As a result, the ionisation of AB is stopped or suppressed.
This establishes the clear concept of a common ion effect for our soluble salts study material. It is defined as the addition of a strong electrolyte resembling the weak electrolyte ions that result in the suppression of the ions present in the weak electrolyte. This is termed a common ion effect.
Conclusion
Through the study material notes on soluble salts, we have explored a variety of simple and complex topics concerning soluble salts. We have talked extensively about the solubility product, the factors influencing the solubility product, and its importance. Solubility product is a constant that affects a reaction immensely. If one can determine the solubility product, determining soluble salts becomes exceedingly easy. The lattice enthalpy, hydration enthalpy, and solvation enthalpy are important factors that concern any reaction. The amount of these enthalpies helps determine the solubility of a solute in a given solvent. The solvation enthalpy must be more than the lattice enthalpy for salt or solute soluble in a given solvent.
