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Ionic Equilibrium refers to the state of equilibrium between unionized molecules and ions in the solution of weak electrolytes. In equilibrium, an ionic substance dissociates into its ions in polar solvents.
- Ionic Equilibrium will result in the formation of ions with their undissociated solute in the solution.
- It involves the ionization of ionic compounds into their ions in polar solvents.
Chemical Equilibrium is a type of reversible reaction in which the concentration of the reactant and the concentration of the products do not change with time.
- Ionic compound aqueous solutions, such as NaCl or CuSO4, are good electrical conductors.
- The concentrations of the reactants and the products remain unchanged.
- The ionic equilibrium includes acid, bases and salts.
Ionic Equilibrium Representation: Xa Yb ⇌ aXb+ + bYa-
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Key Terms: Ionic Equilibrium, Electrolytes, Ostwald Dilution Law, Nature of Solute, Nature of Solvent, Equilibrium, Ions, Solutions, Solute, Solvent, Degree of Dissociation, Molecules, Ionic Compounds, Ionization
What is Ionic Equilibrium?
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Ionic equilibrium is a type of equilibrium that establishes a relation between an ionic compound and its dissociated ions in the solution. It helps study weak electrolytes and their effect on weak electrolytes.
- Electrolytes are chemical substances that have the ability to conduct electricity in aqueous or molten states.
- In ionic equilibrium, ionic substances are separated into ions in polar solvents.
- Reactant to product conversion never exceeds 100% because reactants and products coexist in equilibrium.
- Equilibrium reactions in polar liquids might involve the breakdown of a nonpolar covalent reactant or the ionization of ionic molecules into ions.
Example of What is Ionic Equilibrium?Example: CH3COOH +H2O → H3O+ + CH3COO–
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Ionic Equilibrium
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Electrolytes
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Electrolytes are compounds that dissolve into their constituent ions in aqueous solution and thus conduct electricity in their aqueous solution or molten state.
- It contains a natural positive or negative electrical charge when dissolved in water.
- The substance helps in the regulation of chemical reactions and maintains the balance between fluids in the cells.
- It consists of a salt solution, an acid solution, a basic solution, and so on.
- Non-electrolytes are compounds that do not disintegrate into anions and cations in a solution.
- Sodium, potassium and chloride are three important electrolytes.
Types of Electrolytes
Strong and weak electrolytes are two types of ionic equilibrium electrolytes whose descriptions are as follows:
Strong Electrolytes
Strong electrolytes are a type of electrolytes that completely dissociate in their ionic solution. The reaction is carried out in one direction. However, in case of a weak electrolyte, the reaction tends to be reversible in nature.
Weak Electrolytes
Weak electrolytes are a type of electrolytes that partially dissociate in their ionic solution.
Example of ElectrolytesExample: NaCl, for example, undergoes complete ionization in aqueous solution, generating sodium ions (Na+) and chloride (Cl–) ions, whereas acetic acid undergoes partial ionization, yielding some acetate ions (CH3COO–) and hydrogen (H+) ions.
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Ionic Equilibrium Formulas
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At equilibrium, it's important to know what fraction of the reactants' initial amount is changed into products. The degree of dissociation/ionization is the proportion of the initial molecules that are transformed at equilibrium.
Degree of Dissociation or Ionization
The degree of dissociation or ionization is given by the formula:
α = (Number of reactant molecules dissociated\ionized at the start)/(Number of reactant molecules at the start)
- where a is the degree of dissociation.
- In ionic equilibrium, the degree of dissociation can be stated as a percentage which can be be expressed as follows:
% Degree of dissociation or ionization (α )= (Number of reactant molecules dissociated or ionized at the start)/(Number of reactant molecules at the start) × 100
Dissociation of Ionic Compounds in Polar Solvents
When analyzing ionic equilibrium, ionic compounds that are dissolved in polar solvents will get ionized into cations and anions. They are in equilibrium with the un-dissociated molecules, which can be expressed as follows:
AxBy ⇌ xAy+ + yBx-
Factors on which the Degree of Dissociation Depends
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An electrolyte's degree of dissociation is determined by the following factors:
Nature of Solute
Some substances, such as mineral acids, alkalies, and most salts, ionize practically fully in aqueous solutions. They are known as strong electrolytes.
- Organic acids and bases ionize to a lower amount, as do some inorganic acids like HCN and inorganic bases like NH4OH.
- They're referred to as weak electrolytes.
Nature of Solvent
Water, which has a high dielectric constant (i.e., insulating power), induces more ionization than alcohol, which has a low dielectric constant. Hydrochloric acid in an aqueous solution conducts electricity quickly.
- However, its solution in toluene (an organic solvent) allows just a small quantity of energy to pass through it.
- Few or no ions are formed in the latter case.
- It consists of high dielectric solvents that increase ionization energy.
Dilution
The more the amount of solvent employed, the greater the amount of ionization. As a result, dilute solutions have a higher degree of ionization than concentrated ones.
Temperature
As the temperature rises, so does ionization.
Nature of Other Substances in Solution
The degree of ionization of one electrolyte is affected by the presence of other electrolytes with the same ion. For example, ammonium hydroxide cannot ionize in the presence of ammonium chloride in solution.
- When another electrolyte with a common ion is added, the degree of ionization of the first electrolyte is suppressed.
Ostwald’s Dilution Law
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According to Ostwald’s Dilution Law, the degree of dissociation of weak electrolytes is inversely proportional to the square root of molar concentration.
- It is directly proportional to the square root of volume having one mole of solute for a weak electrolyte.
- The application includes the law of mass action to weak electrolytes in solution.
- The equation is invented for the fluctuation of an electrolyte’s degree of ionisation with a dilution of solution.
- Dilution raises the degree of ionization.
- As a result, the square root of dilution is proportional to the degree of dissociation of a weak electrolyte.
- Mathematically, it can be represented as:
Ka=a²C/(1-a)
and α =√KV
- The binary electrolyte AB dissociates into the ions A+ and B–.
A+ + B– = AB
- Any ion concentration = Cα = √CK = √K/V.
- For extremely weak electrolytes, α <<< 1, (1 – α) = 1
Common Ion Effect on Degree of Dissociation
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The Common Ion Effect refers to the process where weak electrolytes are poorly ionized in an aqueous solution. Their ionization energy is further reduced if one of the ions is added from another source.
Some common examples of the Common Ion Effect on the Degree of Dissociation are as follows:
Ammonium Hydroxide
Ammonium hydroxide is generally a weak base. When ammonium chloride is added to the weak base, then ammonium ions will combine with the hydroxide ions to form unionized ammonium hydroxide.
NH4Cl → NH4+ + Cl–
NH4OH ⇌ NH4+ + OH–
Hydrolysis of Oil
In the case of hydrolysis of oil then in such case, sodium salt of fatty acid is found in a dissolved state. The concentration of sodium ions increases when sodium chloride is added to the solution.
CnH2n+1 + COONa ⇌ CnH2n+1 COO– + Na+
NaCl ⇌ Na+ + Cl–
When the ionic product of [CnH2n+1COO–] [Na+] exceeds the solubility product of soap, then soap is precipitated out of the solution, which is called salting out of soap.
Manufacture of Sodium Bicarbonate
The manufacture of sodium bicarbonate will result in the formation of baking soda. It is carried out with the help of the Solvay process. In Solvay’s process, the carbon dioxide is passed through a solution of ammonical brine, which will precipitate out NaHCO3.
NH4OH + CO2 → NH4HCO3
NH4HCO3 + NaCl → NH4HCO3 + NH4Cl
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Things to Remember
- Notes on Ionic equilibrium will help students prepare for the NCERT Class 11 Chemistry examination.
- It specifies the relation between unionised molecules and ions in the solution of weak electrolytes.
- In equilibrium, the rate of forward reaction is equal to the rate of backward reaction.
- The degree of dissociation depends upon the nature of the solute, solvent and other substances present in the solution.
- Chemical reactions in solutions, particularly aqueous solutions, are crucial in chemistry.
- Due to the common ion effect, the solubility of a sparingly soluble salt is reduced.
Sample Questions
Ques. What is equilibrium? (2 marks)
Ans. Equilibrium is a state of balance or rest that occurs when opposing forces act in the same way. A stable equilibrium in which the opposing sides cancel each other out and no additional changes in the system's attributes occur.
Ques. The degree of dissociation of weak electrolytes increases by? (2 marks)
Ans. When more solvent is added to the solution, it helps in dissociating the molecules into ions of a weak electrolyte. Thus, the degree of dissociation of the weak electrolyte increases upon dilution.
Ques. What is the initial effect of the change on vapour pressure? (2 marks)
Ans. If the volume of the container is suddenly increased, then the vapour pressure would decrease initially. This is because the amount of vapour remains the same, but the volume increases suddenly. As a result, the same amount of vapour is distributed in a larger volume.
Ques. How do rates of evaporation and condensation change initially? (2 marks)
Ans. Since the temperature is constant, the rate of evaporation also remains constant. When the volume of the container is increased, the density of the vapour phase decreases. As a result, the rate of collisions of the vapour particles also decreases. Hence, the rate of condensation decreases initially.
Ques. What happens when equilibrium is restored finally and what will be the final vapour pressure? (2 marks)
Ans. When equilibrium is restored finally, the rate of evaporation becomes equal to the rate of condensation. In this case, only the volume changes while the temperature remains constant. The vapour pressure depends on temperature and not on volume. Hence, the final vapour pressure will be equal to the original vapour pressure of the system.
Ques. What are the Arrhenius Theory's Three Postulates? (3 marks)
Ans. The three main postulates of this hypothesis are as follows:
- When an electrolyte dissolves in water, it forms ions, which are charged particles. Ions recombine to generate a unionised electrolyte.
- As a result, a dynamic or ionic equilibrium is achieved between the generated ions and the ionised electrolyte.
- When electrolytes are dissolved in water, they ionise almost entirely. Strong electrolytes are what they're called.
Ques. Ionic conductance of hydrated M + ions is in the order (3 marks)
Ans. Ionic conductance in aqueous medium of ions α radius of hydrated ions. As mobility of ions is inversely proportional to the size of their hydrated ions. The degree of hydration decreases with ionic radius. Thus, radius of hydrated ions decreases with increase in size of ions. As we move down the group, Size of an ions increases → Degree of hydration decreases → radius of hydrated ions decreases → Ionic conductance increases. So, order of ionic conductance will be Li + <Na + <K + <Rb + <Cs
Ques. What reactions are used in manufacturing of sodium bicarbonate? (2 marks)
Ans. The reactions used in manufacturing of sodium bicarbonate are as follows:
NH4OH + CO2 → NH4HCO3
NH4HCO3 + NaCl → NH4HCO3 + NH4Cl
Ques. What is the difference between static and dynamic equilibrium? (3 marks)
Ans. The difference between static and dynamic equilibrium are as follows:
| Static Equilibrium | Dynamic Equilibrium |
|---|---|
| Static equilibrium is a type of irreversible reaction. | Dynamic equilibrium is a type of reversible reaction. |
| It occur in open and closed system. | It occur in closed system. |
| In this rate of forward and backward reaction is equal to zero. | In this rate of forward and backward reaction is equal. |
Ques. What is the difference between strong and weak electrolyte? (2 marks)
Ans. The difference between strong and weak electrolyte are as follows:
| Strong Electrolyte | Weak Electrolyte |
|---|---|
| Strong electrolytes are a type of electrolytes that completely dissociate in their ionic solution. | Weak electrolytes are a type of electrolytes that partially dissociate in their ionic solution. |
| It include strong acids and strong bases. | It include weak acids and weak bases. |
Ques. What are the factors that affect the degree of dissociation? (5 marks)
Ans. The factors that affect the degree of dissociation depends are as follows:
- Nature of Solute: In aqueous solutions, several compounds ionize nearly completely, including most salts, alkalies, and mineral acids. They are referred to as powerful electrolytes. Certain inorganic acids and bases, such as HCN and NH4OH, as well as organic acids and bases, ionize to a lesser extent.
- Nature of Solvent: Alcohol has a low dielectric constant, but water has a high dielectric constant, or insulating power, which causes more ionization. In an aqueous solution, hydrochloric acid conducts electricity rapidly; however, when it is dissolved in toluene, an organic solvent, very little energy can flow through since little to no ions are generated.
- Dilution: The amount of ionization increases with the amount of solvent used. Consequently, the degree of ionization in diluted solutions is larger than in concentrated ones.
- Temperature: Ionization increases in tandem with temperature.
- Other Substances' Nature in Solution: Additional Materials in Solution: The presence of other electrolytes containing the same ion affects the degree of ionization of one electrolyte. For example, ammonium hydroxide cannot ionize in solution containing ammonium chloride. The degree to which the first electrolyte is ionized is suppressed when another electrolyte containing a common ion is added.
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