Ch.18 - Aqueous Ionic Equilibrium

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.18 - Aqueous Ionic Equilibrium

Problema 48a

Capitolo 18, Problema 48a

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?

Guida verificata passo dopo passo

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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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.

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03:02

Buffer Solutions

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.

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02:40

Henderson-Hasselbalch Equation

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.

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04:30

Acid-Base Indicators

Pratica correlata

Domanda del libro di testo

A 100.0-mL buffer solution is 0.175 M in HClO and 0.150 M in NaClO. c. What is the pH after addition of 85.0 mg of NaOH?

900

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Domanda del libro di testo

A 100.0-mL buffer solution is 0.175 M in HClO and 0.150 M in NaClO. b. What is the pH after addition of 150.0 mg of HBr?

427

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Domanda del libro di testo

What mass of sodium benzoate should you add to 150.0 mL of a 0.15 M benzoic acid solution to obtain a buffer with a pH of 4.25? (Assume no volume change.)