Pyridine is a weak base that is used in the manufacture of pesticides and plasti

Question

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 OH The pKG of pyridine is 8.75. What is the pH ofa0.165M solution of pyridine? Express the pH numerically to two decimal places. pH Subrit Hints My Answers Give Up Review Part Part B Benzoic acid is a weak acid that has antimicrobial properties. Its sodium salt, sodum benzoate, is a preservative found in foods, medications, and personal hygiene products. Benzoic acid dissociates in water The pKa of this reaction 42 In a 0.72Msolution of benzoic acid, what percentage of the molecules are ionized? Express the percentage numerically using two significantfigures. percent ionized

Explanation / Answer

Hi,

Pkb = 8.75,

Pkb = -log[kb] = 8.75

Kb = 1.77 * 10^-9.

Kb = [C6H5NH+][OH-]/ [C6H5N] = [X][X]/0.165

1.77*10^-9 = [x]^2 /0.165.

[x] = 1.73 * 10^-5. Here x is [OH]

Poh = -log[OH] = 4.76

Ph = 14 - poh = 9.24.

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Pka = 4.2

Pka = -log[ka] = 4.2

Ka = 6.3 * 10^-5

Kb = [C6H5COO-][H+]/[C6H5COOH] = [X][X]/0.72

6.3*10^-5 = [x]^2/0.72

[x]= 6.74 * 10^-3 . Here x is [H]

Ph= - log[H+] = 2.17.

% ionized = conc of H / conc of benzoic acid = 6.74*10^-3 /0.72 = 0.936 %

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