A 100.0-mL buffer solution is 0.175 M in HClO and 0.150 M in NaClO. a. What is the initial pH of this solution?

Verified step by step guidance

Step 1: Identify the acid and its conjugate base in the buffer solution. In this case, HClO is the weak acid and ClO- (from NaClO) is its conjugate base.

Step 2: Use the Henderson-Hasselbalch equation to calculate the pH of the buffer solution. The equation is pH = pKa + log([A-]/[HA]), where [A-] is the molarity of the base (ClO-) and [HA] is the molarity of the acid (HClO).

Step 3: Look up the Ka value for HClO in a table of acid dissociation constants. Then, calculate the pKa by taking the negative logarithm of the Ka value.

Step 4: Substitute the values of pKa, [A-], and [HA] into the Henderson-Hasselbalch equation to calculate the pH.

Step 5: If the pH is less than 7, the solution is acidic. If the pH is greater than 7, the solution is basic. If the pH is 7, the solution is neutral. In this case, since we have a buffer solution, the pH should be close to the pKa value of the weak acid.

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Key Concepts

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

Buffer Solutions

Buffer solutions are mixtures that 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 this case, the buffer is made up of hypochlorous acid (HClO) and sodium hypochlorite (NaClO), which work together to maintain the pH of the solution.

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It is expressed as pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base and [HA] is the concentration of the weak acid. This equation is essential for determining the pH of the given buffer solution containing HClO and NaClO.

pKa and Acid-Base Equilibria

pKa is the negative logarithm of the acid dissociation constant (Ka) and indicates the strength of an acid in solution. A lower pKa value signifies a stronger acid. Understanding the pKa of HClO is crucial for applying the Henderson-Hasselbalch equation to find the initial pH of the buffer solution, as it reflects the equilibrium between the acid and its conjugate base.