Textbook Question
The equilibrium constant Kn for the neutralization of lactic acid (C3H6O3) and urea (CH4N2O) is 2.1 x 10^-4. What is Kb for urea? The Ka of lactic acid is 1.4 x 10^-4.
Ch.17 - Applications of Aqueous Equilibria
Chapter 17, Problem 56
Does the pH increase, decrease, or remain the same on the addition of each of the following? (a) NH4NO3 to an NH3 solution (b) Na2CO3 to an NaHCO3 solution (c) NaClO4 to an NaOH solution
Verified step by step guidance1
Identify the nature of each compound involved in the problem. NH4NO3 is an ammonium salt, NH3 is a weak base, Na2CO3 is a basic salt, NaHCO3 is a weak acid, NaClO4 is a neutral salt, and NaOH is a strong base.
For part (a), consider the reaction of NH4NO3 with NH3. NH4NO3 dissociates into NH4+ and NO3-. NH4+ is the conjugate acid of NH3, which can donate a proton to water, slightly increasing the acidity of the solution and thus decreasing the pH.
For part (b), consider the addition of Na2CO3 to NaHCO3. Na2CO3 dissociates into 2 Na+ and CO3^2-. CO3^2- is a stronger base than HCO3-, so it will react with water to form OH- ions, increasing the pH of the solution.
For part (c), analyze the effect of adding NaClO4 to NaOH. NaClO4 dissociates into Na+ and ClO4-. Both ions are neutral in terms of acid-base chemistry, so they do not affect the pH of the NaOH solution, which remains the same.
Summarize the effects: (a) pH decreases due to the acidic nature of NH4+, (b) pH increases due to the basic nature of CO3^2-, and (c) pH remains the same as NaClO4 does not affect the basicity of NaOH.
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). The pH scale measures the acidity or basicity of a solution, with lower values indicating higher acidity and higher values indicating higher basicity. Understanding how acids and bases interact is crucial for predicting changes in pH when different substances are added to a solution.
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Arrhenius Acids and Bases
Buffer Solutions
Buffer solutions are mixtures that can resist changes in pH upon the addition of small amounts of acids or bases. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. The addition of substances like NH4NO3 or Na2CO3 to buffer solutions can affect the equilibrium between the acid and base components, thus influencing the pH.
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Salt Hydrolysis
Salt hydrolysis refers to the reaction of a salt with water to produce an acidic or basic solution. When salts like NH4NO3 or Na2CO3 dissolve in water, they can dissociate into their constituent ions, which may interact with water to form either H+ or OH- ions, thereby altering the pH. Understanding the nature of the ions produced is essential for predicting the pH change in a solution.
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