Unlike strong acids and bases that ionize completely in solution, weak acids or

Question

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 K_a or K_b. pK_a or pK_b. and percent ionization. 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: C_5H_5N + H_2O C_5H_5NH^+ + OH^- The pK_b of pyridine is 8.75. What is the pH of a 0.215 M solution of pyridine? Express the pH numerically to two decimal places. 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. C_6H_5COOH C_6 H_5 COO^- + H^+ The pK_a of this reaction is 4.2. In a 0.64 M solution of benzoic acid, what percentage of the molecules are ionized? Express the percentage numerically using two significant figures.

Explanation / Answer

Pyridine is weak base that is used

The pKb of Pyridine is 8.75 what is the ph of a 0.215 M solution of Pyridin

Kb = 10^-8.75 = 2 x 10^-9

2 x 10^-9 = x^2 / 0.215 - x

square root of 4.3e-10

x = [OH-]= 0.0000207 M

pOH = -log[OH-] = -log(2 X 10-5)

pOH = 4.69

pH = 14 - 4.69 =9.31----------answer

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The pKb of this reaction is 4.2 in a 0.64 M solution of benzoic acid what percentage of the molecules are ionized

Ka = 10^-4.2 = 6.3 x 10^-5

6.3 x 10^-5 = x^2/ 064 -x
x = 0.0063 M
% = 0.0063 x 100/ 0.64=0.984 % ionized

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