Textbook Question
Calculate Kb values for CH3COO- and ClO-.
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Ch.16 - Acid-Base Equilibria
Chapter 16, Problem 79
Using data from Appendix D, calculate [OH-] and pH for each of the following solutions: (a) 0.10 M NaBrO (b) 0.080 M NaHS (c) a mixture that is 0.10 M in NaNO2 and 0.20 M in Ca(NO3)2.
Verified step by step guidance1
Step 1: Identify the relevant chemical species in each solution and determine if they are acids, bases, or salts. For example, NaBrO is a salt of a weak acid (HBrO), NaHS is a salt of a weak acid (H2S), and NaNO2 is a salt of a weak acid (HNO2).
Step 2: For each solution, write the equilibrium expression for the hydrolysis reaction of the anion. For example, for NaBrO, the hydrolysis reaction is BrO^- + H2O \rightleftharpoons HBrO + OH^-. Use the equilibrium constant expression K_b = \frac{[OH^-][HBrO]}{[BrO^-]} to find [OH^-].
Step 3: Use the relationship between the equilibrium constants of the acid and its conjugate base: K_w = K_a \times K_b, where K_w is the ion-product constant of water (1.0 \times 10^{-14} at 25°C). Calculate K_b using the given K_a values from Appendix D.
Step 4: Solve for [OH^-] using the equilibrium expression and the initial concentration of the salt. Assume that the change in concentration of the salt is negligible compared to its initial concentration.
Step 5: Calculate the pH of the solution using the relationship pH + pOH = 14. First, find pOH from [OH^-] using pOH = -\log[OH^-], then calculate pH.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Chemistry
Acid-base chemistry involves the study of substances that can donate protons (acids) or accept protons (bases). Understanding the properties of acids and bases is crucial for calculating hydroxide ion concentration [OH-] and pH, as these values are directly influenced by the dissociation of acids and bases in solution.
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Arrhenius Acids and Bases
pH and pOH Scale
The pH scale measures the acidity or basicity of a solution, with lower values indicating higher acidity and higher values indicating higher basicity. The pOH scale is similarly used for basicity, and the relationship between pH and pOH is given by the equation pH + pOH = 14. This relationship is essential for converting between [OH-] and pH.
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Buffer Solutions
Buffer solutions are mixtures that can resist changes in pH upon the addition of small amounts of acids or bases. In the context of the question, understanding how the components of the solutions (like NaBrO and NaNO2) interact with water and each other is vital for determining their effect on [OH-] and pH, especially in mixed solutions.
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Related Practice
Textbook Question
Given that Kb for ammonia is 1.8 × 10-5 and that for hydroxylamine is 1.1 × 10-8, which is the stronger base?
Textbook Question
Which is the stronger acid, the ammonium ion or the hydroxylammonium ion?
Textbook Question
Using data from Appendix D, calculate 3OH-4 and pH for each of the following solutions: (b) 0.035 M Na2S
Textbook Question
Pyridinium bromide 1C5H5NHBr2 is a strong electrolyte that dissociates completely into C5H5NH+ and Br-. An aqueous solution of pyridinium bromide has a pH of 2.95. (a) Write out the reaction that leads to this acidic pH.