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Ch.16 - Acid-Base Equilibria
Chapter 16, Problem 58

A 0.100 M solution of bromoacetic acid 1BrCH2COOH2 is 13.2% ionized. Calculate 3H+4, 3BrCH2COO-4, 3BrCH2COOH4 and Ka for bromoacetic acid.

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1
Identify the initial concentration of bromoacetic acid, which is 0.100 M.
Determine the concentration of ionized bromoacetic acid using the given ionization percentage: 13.2% of 0.100 M.
Calculate the concentrations of \([\text{H}^+]\) and \([\text{BrCH}_2\text{COO}^-]\) since they are equal to the concentration of ionized bromoacetic acid.
Find the concentration of the non-ionized bromoacetic acid \([\text{BrCH}_2\text{COOH}]\) by subtracting the ionized concentration from the initial concentration.
Use the expression for the acid dissociation constant \(K_a = \frac{[\text{H}^+][\text{BrCH}_2\text{COO}^-]}{[\text{BrCH}_2\text{COOH}]}\) to calculate \(K_a\).

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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 bromoacetic acid, do not fully dissociate in solution. The degree of ionization indicates how much of the acid has converted to its ions, which is crucial for calculating concentrations of the species in solution. In this case, a 13.2% ionization means that 13.2% of the bromoacetic acid molecules have dissociated into H+ and BrCH2COO- ions.
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Equilibrium Constant (Ka)

The acid dissociation constant (Ka) quantifies the strength of a weak acid in solution. It is calculated using the concentrations of the products and reactants at equilibrium. For bromoacetic acid, Ka can be determined from the concentrations of H+, BrCH2COO-, and BrCH2COOH at equilibrium, reflecting the extent of ionization.
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Concentration Calculations

To find the concentrations of H+, BrCH2COO-, and BrCH2COOH, one must apply the initial concentration and the degree of ionization. For a 0.100 M solution that is 13.2% ionized, the concentration of H+ and BrCH2COO- can be calculated as 0.0132 M, while the remaining concentration of BrCH2COOH can be found by subtracting the ionized amount from the initial concentration.
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