The relative concentrations of o − ethylbenzoic acid and potassium o − ethylbenzoate required to prepare a buffer with pH = 4.0 has to be calculated. Concept Introduction: The buffer is a solution that resists any change in pH on addition of H + and OH − . An acidic buffer is made up of a weak acid and its salt. A basic buffer is made up of a weak base and its salt. The formula to calculate the pH of the buffer is shown below. pH = − p K a + log [ A − ] [ HA ]

Question

You are asked to prepare a pH = 3.00 buffer starting from 2.00 L of 0.025 M solution of benzoic acid (C6H5COOH). (a) What is the pH of the benzoic acid solution prior to adding sodium benzoate? (hint: write the reaction equation for the acid dissociation and then use the equilibrium constant expression to calculate [H + ]) (b) How many grams of sodium benzoate should be added to prepare the buffer? Neglect the small volume change that occurs when the sodium benzoate is added.(hint: use the equilibrium constant expression to calculate [C6H5COO− ] in the buffer)

Answer 1

Question

Chapter 15, Problem 87QRT

Interpretation Introduction

Interpretation:

The relative concentrations of o−ethylbenzoic acid and potassium o−ethylbenzoate required to prepare a buffer with pH=4.0 has to be calculated.

Concept Introduction:

The buffer is a solution that resists any change in pH on addition of H+ and OH−. An acidic buffer is made up of a weak acid and its salt. A basic buffer is made up of a weak base and its salt. The formula to calculate the pH of the buffer is shown below.

pH=−pKa+log[A−][HA]

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