Model 2: A strong base increases the hydroxide ion concentration by a stoichiometric amount because it dissociates almost completely. For a weak base, only a small fraction of the base molecules accept a H* from water. Since water molecules that have given their H* to the base are now OH ions, this increases the hydroxide ion concentration of a solution, but the amount of increase is small. When a base accepts a H+ ion, this is called a base ionization reaction, and the equilibrium constant associated with this reaction is called Kb. OH- Na+ B HB+ Problems A solution of a strong base, NaOH Key Questions 1. Write out a reaction between a weak base, B, and water. (H₂O molecules are not shown) A solution of a weak base, E 1. Based on your reaction in Key Question (1) for this model, what is the expression for Kb? = 2. Pyridine, C5H5N, is a weak base that reacts in water and has a Kb 1.7 x 10⁹ at 25°C. (a) Write out the base ionization reaction between pyridine and water. (b) Write out the equilibrium expression for the Kь of pyridine in water. (c) If 0.30 moles of C5H5N are added to water to make a 1.0 L solution at 25°C, what would be the concentration of all species at equilibrium?
Model 2: A strong base increases the hydroxide ion concentration by a stoichiometric amount because it dissociates almost completely. For a weak base, only a small fraction of the base molecules accept a H* from water. Since water molecules that have given their H* to the base are now OH ions, this increases the hydroxide ion concentration of a solution, but the amount of increase is small. When a base accepts a H+ ion, this is called a base ionization reaction, and the equilibrium constant associated with this reaction is called Kb. OH- Na+ B HB+ Problems A solution of a strong base, NaOH Key Questions 1. Write out a reaction between a weak base, B, and water. (H₂O molecules are not shown) A solution of a weak base, E 1. Based on your reaction in Key Question (1) for this model, what is the expression for Kb? = 2. Pyridine, C5H5N, is a weak base that reacts in water and has a Kb 1.7 x 10⁹ at 25°C. (a) Write out the base ionization reaction between pyridine and water. (b) Write out the equilibrium expression for the Kь of pyridine in water. (c) If 0.30 moles of C5H5N are added to water to make a 1.0 L solution at 25°C, what would be the concentration of all species at equilibrium?
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Question
Transcribed Image Text:Model 2: A strong base increases the hydroxide ion concentration by a stoichiometric amount because it
dissociates almost completely. For a weak base, only a small fraction of the base molecules accept a H* from
water. Since water molecules that have given their H* to the base are now OH ions, this increases the
hydroxide ion concentration of a solution, but the amount of increase is small. When a base accepts a H+ ion,
this is called a base ionization reaction, and the equilibrium constant associated with this reaction is called Kb.
OH
Na+
B
HB+
Problems
A solution of a strong base, NaOH
Key Questions
1. Write out a reaction between a weak base, B, and water.
A solution of a weak base, B
(H₂O molecules are not shown)
1. Based on your reaction in Key Question (1) for this model, what is the expression for Kb?
2. Pyridine, C5H5N, is a weak base that reacts in water and has a Kb = 1.7 x 10⁹ at 25°C.
(a) Write out the base ionization reaction between pyridine and water.
(b) Write out the equilibrium expression for the Kь of pyridine in water.
(c) If 0.30 moles of C5H5N are added to water to make a 1.0 L solution at 25°C, what would be the
concentration of all species at equilibrium?
(d) Is the initial concentration of C5H5N similar to the equilibrium concentration? Why?
- 4-
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