Write the chemical equation and the Kb expression for the reaction of each of the following bases with water: (a) propylamine, C3H7NH2

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Identify the base and its reaction with water: Propylamine (\(\text{C}_3\text{H}_7\text{NH}_2\)) is a weak base that reacts with water to accept a proton, forming its conjugate acid and hydroxide ions.

Write the balanced chemical equation for the reaction: \[ \text{C}_3\text{H}_7\text{NH}_2 (aq) + \text{H}_2\text{O} (l) \rightleftharpoons \text{C}_3\text{H}_7\text{NH}_3^+ (aq) + \text{OH}^- (aq) \]

Identify the species involved in the equilibrium: The base (\(\text{C}_3\text{H}_7\text{NH}_2\)), water (\(\text{H}_2\text{O}\)), the conjugate acid (\(\text{C}_3\text{H}_7\text{NH}_3^+\)), and hydroxide ions (\(\text{OH}^-\)).

Write the expression for the base dissociation constant (\(K_b\)): \[ K_b = \frac{[\text{C}_3\text{H}_7\text{NH}_3^+][\text{OH}^-]}{[\text{C}_3\text{H}_7\text{NH}_2]} \]

Understand the significance of \(K_b\): The \(K_b\) value indicates the strength of the base; a larger \(K_b\) means a stronger base.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Bronsted-Lowry Theory

The Bronsted-Lowry theory defines acids as proton donors and bases as proton acceptors. In the context of the reaction of propylamine with water, propylamine acts as a base by accepting a proton from water, which in turn acts as an acid. This theory is essential for understanding how bases interact with water to form hydroxide ions.

Chemical Equilibrium

Chemical equilibrium refers to the state in which the concentrations of reactants and products remain constant over time, as the forward and reverse reactions occur at the same rate. In the case of propylamine reacting with water, the equilibrium between the base and its conjugate acid is crucial for determining the extent of the reaction and the concentrations of species involved.

Kb Expression

The Kb expression quantifies the strength of a base in water by measuring the equilibrium constant for its dissociation. For propylamine, the Kb expression is derived from the equilibrium concentrations of the products (propylammonium ion and hydroxide ion) and the reactants (propylamine and water). This expression is vital for calculating the base's dissociation in aqueous solution.