Determining Ionic Strength
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.
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+H2O?C5H5NH++OH?
The pKb of pyridine is 8.75. What is the pH of a 0.150M solution of pyridine?
pH =
Part B
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 ionizes in water:
C6H5COOH?C6H5COO?+H+
The pKa of this reaction is 4.2. In a 0.51Msolution of benzoic acid, what percentage of the molecules are ionized?
percent ionized = |
Part-A: Ionization reaction of pyridine in water is
C5H5N+H2O ---> C5H5NH+ + OH-
Init: 0.150M 0M 0M
Eqm: (0.150-x)M xM xM
Given pKb of pyridine is 8.75
=> - logKb = 8.75
=> Kb = antilog(-8.75) = 1.78*10-9
Now Kb can also be calculated as
Kb = [C5H5NH+]*[OH-] / [C5H5N] = x*x / (0.150-x) = x2 /(0.150-x)
= >1.78*10-9 = x2 /(0.150-x)
Since x << 0.150, (0.150-x) is nearly equals to 0.150
=> x = underroot(0.150*1.78*10-9) = 1.63*10-5 M
=> x = [OH-] = 1.63*10-5 M
=> pOH = - log[OH-] = -log(1.63*10-5) = 4.79
=> pH = 14 – pOH = 14 – 4.79 = 9.21 (answer)
Part-B: Let the degree of ionization of benzoic acid be
Given [C6H5COOH], C = 0.51M
C6H5COOH --> C6H5COO- + H+
Init: 0.51M 0M 0M
eqm: 0.51(1 - )M 0.51M 0.51M
Given pKa = 4.2
=> - logKa = 4.2
=>Ka = antilog(-4.2) = 6.3*10-5
Now Ka can also be calculated as
Ka = [C6H5COO- ]*[H+] / [C6H5COOH] = ( 0.51M)*(0.51M) / 0.51(1 - )M
=> 6.3*10-5 = ( 0.51M)*(0.51M) / 0.51(1 - )M
Since <<1 , (1 - ) is nearly equals to 1. Hence
6.3*10-5 = 0.512
=> = 1.11x10-2
Hence percentage ionisation = *100 = 1.11 % (answer)
Determining Ionic StrengthUnlike strong acids and bases that ionize completely in solution, weak acids...
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+H2O⇌C5H5NH++OH− The pKb of pyridine is 8.75. What is the pH of a 0.185 M solution of pyridine? (Assume that the temperature is 25 ∘C.) Part B Benzoic acid is a weak acid that has antimicrobial properties. Its sodium salt, sodium benzoate, is a preservative found in foods,...
Thank you in advance. 1) 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? The pKb of pyridine is 8.75. What is the pH of a 0.305M 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...
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+H2O⇌C5H5NH++OH−C5H5N+H2O⇌C5H5NH++OH− The pKbpKb of pyridine is 8.75. What is the pHpH of a 0.265 MM solution of pyridine? Express the pHpH numerically to two decimal places. Part B Benzoic acid is a weak acid that has antimicrobial properties. Its sodium salt, sodium benzoate, is a preservative found in...
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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− The pKb of pyridine is 8.75. What is the pH of a 0.200 M solution of pyridine? (Assume that the temperature is 25 ∘C.) Express the pH numerically to two decimal places.
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− The pKb of pyridine is 8.75. What is the pH of a 0.360 M solution of pyridine? Express the pH numerically to two decimal places. If we get numbers from somewhere other than whats given can it be labeled Ex:Formulas
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 ionizes in water: C6H5COOH⇌C6H5COO−+H+ The pKa of this reaction is 4.2. In a 0.62 M solution of benzoic acid, what percentage of the molecules are ionized? Express your answer to two significant figures and include the appropriate units.
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⇌C6H5COO−+H+ The pKa of this reaction is 4.2. In a 0.76 M solution of benzoic acid, what percentage of the molecules are ionized? Express the percentage numerically using two significant figures.
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