CHM 2354 Lecture Notes - Lecture 7: Acid Dissociation Constant, Equilibrium Constant, Rice Chart

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25 May 2015

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Weak acids and bases do not completely dissociate. Ka, the dissociation for the acid ha is. Kb, the dissociation for the acid ha is pk is the negative logarithm of the equilibrium. The higher the pka, the lower the ka, but pk are simpler to write. Conjugate acid-base pairs are related by the gain or loss of a proton. A weak" makes a weak" and a strong" makes a very weak because it dissociates completely. Any effect that increases the stability of the product drives the reaction forward. A lower pka means it is more stable (higher ka). A higher pka means it is less stable (lower ka). Unlike with concentrated strong acid we need to account for water ionization. Find the ph for a solution of a general weak acid ha is below 1. 0 x 10-8 constant. (ka. The [h+] represents the protons from both sources: f is the total ph (dissociated + non dissociated)

Related Questions

Unlike strong acids and bases that ionize completely in solution, weak acids or bases partially ionize. The tendency to ionize (i.e., the ionic strength) of a weak acid or base can be quantified in several ways including;

Ka or Kb, pKa or pKb, and percent ionization.

Benzoic acid is a weak acid that has antimicrobial properties. Its sodium salt, sodium benzoate, is a preservative found in foods, medications, and personal hygiene products. Benzoic acid dissociates in water:

C6H5COOH(aq)+H2O(l)âC6H5COOâ(aq)+H3Oâ(aq)

The pKa of this reaction is 4.2. In a 0.80 mol Lâ1 solution of benzoic acid, what percentage of the molecules are ionized?

Express your answer to two significant figures and include the appropriate units.

Ka or Kb,

pKa or pKb,

and percent ionization.

Part A

Pyridine is a weak base that is used in the manufacture of pesticides and plastic resins. It is also a component of cigarette smoke. Pyridine ionizes in water as follows:

C5H5N+H2OâC5H5NH++OHâ

The pKb of pyridine is 8.75. What is the pH of a 0.455 M solution of pyridine?

Express the pH numerically to two decimal places.

pH=____________

Part B

C6H5COOHâC6H5COOâ+H+

The pKa of this reaction is 4.2. In a 0.58 M solution of benzoic acid, what percentage of the molecules are ionized?

Express the percentage numerically using two significant figures.

percent ionized = _______________ %

CHM 2354 Lecture Notes - Lecture 7: Acid Dissociation Constant, Equilibrium Constant, Rice Chart

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