Explain what the Kb for aniline ( C6H5NH2 ) tells you ( Kb = 4.3 × 10-10 ).
A small number like 4.3E-10 says that very few of the aniline molecules ionize and that equilibrium you have most of the molecules of aniline intact; i.e., mostly aniline, a few H^+, and a few [C6H5NH3]^+
The Kb for aniline (C6H5NH2) is a measure of its basicity. It tells us the strength of aniline as a base in aqueous solution.
Specifically, the Kb value is the equilibrium constant for the reaction of aniline with water to produce its conjugate acid (C6H5NH3+) and hydroxide ion (OH-). The equation for this reaction is:
C6H5NH2 + H2O ⇌ C6H5NH3+ + OH-
The Kb value represents the degree to which the reaction favors the formation of the products. In this case, a lower Kb value indicates a weaker base because the equilibrium lies more towards the reactant side. Conversely, a higher Kb value suggests a stronger base because the equilibrium is shifted more towards the product side.
In the case of aniline with a Kb value of 4.3 × 10^-10, it has a very small Kb value, indicating that aniline is a weak base.
The Kb value for a compound is its base dissociation constant, which tells you the extent to which it ionizes in water to produce hydroxide ions (OH-) and the corresponding conjugate acid. In the case of aniline (C6H5NH2), it is a weak base that does not fully dissociate in water. The Kb value of 4.3 × 10-10 indicates the strength of aniline as a base.
To understand what Kb tells you, you first need to know about the concept of equilibrium, which occurs when the rate of the forward reaction equals the rate of the reverse reaction. In the case of a base like aniline, the equilibrium is reached when some molecules of aniline react with water to produce hydroxide ions and the conjugate acid, whereas some hydroxide ions and the conjugate acid react to reform aniline molecules.
The Kb value is a measure of the equilibrium constant for the dissociation reaction of the base. It is defined as the ratio of the concentration of the hydroxide ions (OH-) and the concentration of the original base (aniline). A larger Kb value indicates a stronger base, suggesting that more hydroxide ions are produced from the dissociation of the base.
For example, a Kb value of 4.3 × 10-10 means that aniline is a relatively weak base, as only a small amount of it ionizes in water. This means that the concentration of hydroxide ions generated from aniline in the water solution is very low compared to the concentration of undissociated aniline molecules.
To determine the concentration of hydroxide ions or the extent of aniline dissociation, you would typically set up an equilibrium expression and use the Kb value to solve for the unknown. However, it's important to note that the actual concentration of hydroxide ions will also depend on the initial concentration of the aniline solution and the specific conditions of the system.