A 0.100 M solution of chloroacetic acid 1ClCH2COOH2 is 11.0% ionized. Using this information, calculate 3ClCH2COO-4, 3H+4, 3ClCH2COOH4, and Ka for chloroacetic acid.

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Identify the initial concentration of chloroacetic acid, \([\text{ClCH}_2\text{COOH}]_0 = 0.100\, \text{M}\).

Determine the concentration of ionized chloroacetic acid using the ionization percentage: \(0.100\, \text{M} \times 0.110 = [\text{ClCH}_2\text{COO}^-] = [\text{H}^+]\).

Calculate the concentration of non-ionized chloroacetic acid: \([\text{ClCH}_2\text{COOH}] = 0.100\, \text{M} - [\text{ClCH}_2\text{COO}^-]\).

Write the expression for the acid dissociation constant, \(K_a = \frac{[\text{ClCH}_2\text{COO}^-][\text{H}^+]}{[\text{ClCH}_2\text{COOH}]}\).

Substitute the concentrations into the \(K_a\) expression to solve for \(K_a\).

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Key Concepts

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

Ionization of Weak Acids

Weak acids, like chloroacetic acid, do not fully dissociate in solution. The degree of ionization indicates how much of the acid has converted to its ions. In this case, an 11.0% ionization means that 11% of the chloroacetic acid molecules have dissociated into ions, which is crucial for calculating concentrations of the species in solution.

Equilibrium Concentrations

To find the concentrations of the ions and the undissociated acid at equilibrium, we use the initial concentration and the degree of ionization. For a 0.100 M solution that is 11.0% ionized, we can calculate the concentrations of ClCH2COO-, H+, and ClCH2COOH by applying the percentage to the initial concentration, which is essential for determining the acid dissociation constant (Ka).

Acid Dissociation Constant (Ka)

The acid dissociation constant (Ka) quantifies the strength of an acid in solution. It is calculated using the equilibrium concentrations of the products and reactants from the ionization reaction. For chloroacetic acid, Ka can be determined using the formula Ka = [H+][ClCH2COO-] / [ClCH2COOH], where the concentrations are derived from the ionization data provided.

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