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Ch.17 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 4th Edition
Tro4th EditionChemistry: A Molecular ApproachISBN: 9780134112831Not the one you use?Change textbook
All textbooksTro 4th EditionCh.17 - Aqueous Ionic EquilibriumProblem 28
Chapter 17, Problem 28

A formic acid solution has a pH of 3.25. Which of these substances will raise the pH of the solution upon addition? Explain your answer. a. HCl b. NaBr c. NaCHO2 d. KCl

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1
insert step 1: Understand that pH is a measure of the acidity or basicity of a solution. A lower pH indicates a more acidic solution, while a higher pH indicates a more basic solution.
insert step 2: Recognize that adding a strong acid like HCl will lower the pH further, making the solution more acidic.
insert step 3: Identify that NaBr and KCl are salts of strong acids and strong bases, which are neutral in solution and will not significantly change the pH.
insert step 4: Note that NaCHO2 (sodium formate) is the salt of a weak acid (formic acid) and a strong base (sodium hydroxide). It will act as a weak base in solution, raising the pH.
insert step 5: Conclude that adding NaCHO2 will raise the pH of the formic acid solution, as it will partially neutralize the acid, making the solution less acidic.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is neutral, below 7 indicates acidity, and above 7 indicates basicity. In this context, a solution with a pH of 3.25 is acidic, meaning it has a higher concentration of hydrogen ions (H+) compared to hydroxide ions (OH-). Understanding the pH scale is essential for determining how different substances will affect the acidity or basicity of the solution.
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Acid-Base Reactions

Acid-base reactions involve the transfer of protons (H+) between substances. Acids donate protons, while bases accept them. When a base is added to an acidic solution, it can neutralize some of the hydrogen ions, thereby increasing the pH. Identifying whether a substance is an acid or a base is crucial for predicting its effect on the pH of the solution.
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Buffer Solutions

Buffer solutions resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base or a weak base and its conjugate acid. In the case of formic acid, which is a weak acid, the addition of a conjugate base (like sodium formate, NaCHO2) can help raise the pH by neutralizing excess H+ ions, making it important to recognize the role of buffers in pH changes.
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Related Practice
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Solve an equilibrium problem (using an ICE table) to calculate the pH of each solution. a. a solution that is 0.195 M in HC2H3O2 and 0.125 M in KC2H3O2 b. a solution that is 0.255 M in CH3NH2 and 0.135 M in CH3NH3Br