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?

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Identify the components of the buffer solution: HClO (weak acid) and NaClO (its conjugate base).

Calculate the initial moles of HClO and NaClO using their concentrations and the volume of the solution.

Determine the moles of HBr added by converting the mass of HBr to moles using its molar mass.

Recognize that HBr is a strong acid and will react completely with the conjugate base (ClO⁻) in the buffer, reducing the moles of ClO⁻ and increasing the moles of HClO.

Use the Henderson-Hasselbalch equation to calculate the new pH of the buffer solution after the reaction: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right) \), where \([\text{base}]\) and \([\text{acid}]\) are the concentrations of ClO⁻ and HClO after the reaction.

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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 composed of hypochlorous acid (HClO) and sodium hypochlorite (NaClO), which help maintain the pH despite the addition of HBr.

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 pKa is the negative logarithm of the acid dissociation constant, [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 after the addition of HBr.

Acid-Base Neutralization

Acid-base neutralization occurs when an acid reacts with a base to form water and a salt, resulting in a change in pH. In this scenario, HBr, a strong acid, will react with the weak base component of the buffer (NaClO) to produce HClO and NaBr. Understanding this reaction is crucial for calculating the new concentrations of the buffer components and the resulting pH.