Textbook Question
(b) Calculate the pH of a buffer formed by mixing 85 mL of 0.13 M lactic acid with 95 mL of 0.15 M sodium lactate.
Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 24
A buffer is prepared by adding 10.0 g of ammonium chloride (NH4Cl) to 250 mL of 1.00 M NH3 solution. (b) Write the complete ionic equation for the reaction that occurs when a few drops of nitric acid are added to the buffer. (c) Write the complete ionic equation for the reaction that occurs when a few drops of potassium hydroxide solution are added to the buffer.
Verified step by step guidance1
Step 1: Identify the components of the buffer solution. The buffer is composed of NH3 (ammonia) and NH4Cl (ammonium chloride). NH3 is a weak base, and NH4+ (from NH4Cl) is its conjugate acid.
Step 2: Consider the addition of nitric acid (HNO3) to the buffer. HNO3 is a strong acid and will react with the base component of the buffer, NH3. Write the chemical equation for this reaction: NH3 + HNO3 -> NH4+ + NO3-.
Step 3: Convert the chemical equation to the complete ionic equation. Since HNO3 is a strong acid, it dissociates completely in water: NH3 + H+ + NO3- -> NH4+ + NO3-. The NO3- ions are spectator ions and do not participate in the reaction.
Step 4: Consider the addition of potassium hydroxide (KOH) to the buffer. KOH is a strong base and will react with the acid component of the buffer, NH4+. Write the chemical equation for this reaction: NH4+ + OH- -> NH3 + H2O.
Step 5: Convert the chemical equation to the complete ionic equation. Since KOH is a strong base, it dissociates completely in water: K+ + OH- + NH4+ -> NH3 + H2O. The K+ ions are spectator ions and do not participate in the reaction.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Buffer Solutions
A buffer solution is a system that resists changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. In this case, the buffer is made from ammonia (NH3) and ammonium chloride (NH4Cl), which helps maintain a stable pH when acids or bases are introduced.
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03:02
Buffer Solutions
Ionic Equations
Ionic equations represent the species that are actually involved in a chemical reaction, showing the ions in their dissociated form. In the context of the buffer, when nitric acid (HNO3) or potassium hydroxide (KOH) is added, the complete ionic equations will illustrate how these strong acids and bases interact with the buffer components, highlighting the formation of products and the ions present.
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Acid-Base Reactions
Acid-base reactions involve the transfer of protons (H+) between reactants. In the case of the buffer, adding nitric acid introduces H+ ions, which react with the ammonia (NH3) to form ammonium ions (NH4+). Conversely, adding potassium hydroxide provides OH- ions, which react with NH4+ to regenerate NH3 and water, demonstrating the buffer's ability to neutralize added acids and bases.
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Related Practice
Textbook Question
You are asked to prepare a pH = 3.00 buffer solution starting from 1.25 L of a 1.00 M solution of hydrofluoric acid (HF) and any amount you need of sodium fluoride (NaF). (a) What is the pH of the hydrofluoric acid solution prior to adding sodium fluoride?
Textbook Question
You are asked to prepare a pH = 3.00 buffer solution starting from 1.25 L of a 1.00 M solution of hydrofluoric acid (HF) and any amount you need of sodium fluoride (NaF). (b) How many grams of sodium fluoride should be added to prepare the buffer solution? Neglect the small volume change that occurs when the sodium fluoride is added.
Textbook Question
You are asked to prepare a pH = 4.00 buffer starting from 1.50 L of 0.0200 M solution of benzoic acid 1C6H5COOH2 and any amount you need of sodium benzoate 1C6H5COONa2. (a) What is the pH of the benzoic acid solution prior to adding sodium benzoate?