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: An Atoms First Approach

2nd Edition

ISBN:9781305079243

Author:Steven S. Zumdahl, Susan A. Zumdahl

Publisher:Steven S. Zumdahl, Susan A. Zumdahl

Chapter13: Acids And Bases

Section: Chapter Questions

Problem 9RQ: What is a salt? List some anions that behave as weak bases in water. List some anions that have no...

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Students are often surprised to learn that organic acids, such as acetic acid, contain OH groups. Actually, all oxyacids contain hydroxyl groups. Sulfuric acid, usually written as H2SO4, has the structural formula SO2(OH)2, where S is the central atom. Identify the acids whose structural formulas are shown below. Why do they behave as acids, while NaOH and KOH are bases? a. SO(OH)2 b. ClO2(OH) c. HPO(OH)2
When all the water is evaporated from a sodium hydroxide solution, solid sodium hydroxide is obtained. However, if you evaporate the water in an ammonium hydroxide solution, you will not produce solid ammonium hydroxide. Explain why. What will remain after the Water is evaporated?
Two strategies are also followed when solving for the pH of a base in water. What is the strategy for calculating the pH of a strong base in water? List the strong bases mentioned in the text that should be committed to memory. Why is calculating the pH of Ca(OH)2 solutions a little more difficult than calculating the pH of NaOH solutions? Most bases are weak bases. The presence of what element most commonly results in basic properties for an organic compound? What is present on this element in compounds that allows it to accept a proton? Table 13-3 and Appendix 5 of the text list Kb values for some weak bases. What strategy is used to solve for the pH of a weak base in water? What assumptions are made when solving for the pH of weak base solutions? If the 5% rule fails, how do you calculate the pH of a weak base in water?
Estimate the pH that results when the following two solutions are mixed. a) 50 mL of 0.3 M CH3COOH and 50 mL of 0.4 M KOH b) 100 mL of 0.3 M CH3COOH and 50 mL of 0.4 M NaOH c) 150 mL of 0.3 M CH3COOH and 100 mL of 0.3 M Ba(OH)2 d) 200 mL of 0.3 M CH3COOH and 100 mL of 0.3 M Ba(OH)2
Using the diagrams shown in Problem 10-117, which of the solutions would have the greatest buffer capacity, that is, greatest protection against pH change, when the following occurs? a. A strong acid is added to the solution. b. A strong base is added to the solution.
The reaction just described is reversible. Deprotonation of the conjugate acid of an organic base by water provides another example of simultaneous making and breaking of sigma bonds. Thus, in the deprotonation of anilinium ion by water, the base is water, which has unshared electrons on the ________ atom. The acid is ________ ion. A pair of ________ electrons on the oxygen atom of water is pushed toward the ________ atom. Simultaneously, the pair of ________ electrons between the hydrogen and ________ atom of the anilinium ion is pushed toward the ________ atom. Thus, the oxygen- ________ sigma bond is made and a hydrogen- ________ sigma bond is broken. The nitrogen atom, which possessed a positive charge, is now ________, and the oxygen atom, which was neutral, now possesses a formal ________ charge.
Which of the diagrams in Problem 10-135 represents the substance that is the weakest electrolyte?
Four solutions of an acid dissolved in water are sketched below, as if under a microscope so powerful individual atoms could be seen. The same volume of solution is shown in each sketch. Rank the solutions by the strength of the dissolved acid. That is, select 1 under the solution of the strongest acid, 2 under the solution of the next strongest acid, and so on. Note: = H,0 Solution 1 Solution 2 (Choose one) (Choose one) Solution 3 Solution 4 (Choose one) (Choose one)
= Predicting the qualitative acid-base properties of salts Consider the following data on some weak acids and weak bases: name nitrous acid 0.1 M KF 0.1 M KI hydrofluoric acid HF 4 acid solution 0.1 M C6H5NH3Br 0.1 M CH3NH3Cl Explanation formula HNO2 4.5 x 10" -4 6.8 x 10-4 Use this data to rank the following solutions in order of increasing pH. In other words, select a '1' next to the solution that will have the lowest pH, a '2' next to the solution that will have the next lowest pH, and so on. Check a pH ✓ choose one 1 (lowest) 2 3 4 (highest) choose one choose one x - 3 ? Kb formula CóHạNH, 4.3×10-10 methylamine CH3NH₂ 4.4 x 10-4 name aniline base * AND 130 tv 3/5 MacBook Air Нап Ⓒ2022 McGraw Hill LLC. All Rights Reserved. Terms of Use | Privacy Center A @ TEA Acc
Consider the following chemical equilibrium for the weak base CN in water: CN (aq) + H₂O(1) HCN(aq) + OH(aq). Which of the following statements is correct when more water is evaporated from system? Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer. a b C d H pH will go up; [OH-]will go up; net amount of OH will go up pH will go down; [OH-] will go up; net amount of OH will go down pH will go down: [OH-] will go down; net amount of OH will go down pH will go up; [OH will go up; net amount of OH will go down X Your answer