약염기 용액 pH. 0.1 M pyridine 수용액의 pH

약염기 용액 pH. 0.1 M pyridine 수용액의 pH

 

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pKb = -logKb = 8.75

Kb = 10^(-8.75)

 

C5H5N + H2O ⇌ C5H5NH^+ + OH^-

 

Kb = [C5H5NH^+][OH^-] / [C5H5N]

= x^2 / (0.1-x) = 10^(-8.75)

( 식 설명 http://ywpop.tistory.com/4294 )

 

또는

 

 

 

0.1-x ≒ 0.1 이라 근사하면

x = sqrt ( 10^(-8.75) * 0.1 )

= 1.3335*10^(-5) = [OH^-]

 

pOH = -log[OH^-] = -log( 1.3335*10^(-5) ) = 4.88

pH = 14 – pOH = 14 – 4.88 = 9.12

 

 

답: 9.12

 

 

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The pKb of pyridine is 8.75. What is the pH of a 0.120 M solution of pyridine?

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 + H2O ⇌ C5H5NH^+ + OH^-

 

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Kb = [C5H5NH^+][OH^-] / [C5H5N]

= x^2 / (0.120-x) = 10^(-8.75)

 

0.120-x ≒ 0.120 이라 근사하면

x = sqrt ( 10^(-8.75) * 0.120 )

= 1.4608*10^(-5) = [OH^-]

 

pOH = -log[OH^-] = -log( 1.4608*10^(-5) ) = 4.84

pH = 14 – pOH = 14 – 4.84 = 9.16