Ch.17 - Additional Aspects of Aqueous Equilibria

Problem 46b,c

Chapter 17, Problem 46b,c

Consider the titration of 30.0 mL of 0.050 M NH₃ with 0.025 M HCl. Calculate the pH after the following volumes of titrant have been added: (b) 20.0 mL (c) 59.0 mL.

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Calculate the initial moles of NH_3 using the formula: \( \text{moles} = \text{concentration} \times \text{volume} \).

Calculate the moles of HCl added using the formula: \( \text{moles} = \text{concentration} \times \text{volume} \).

Determine the limiting reactant by comparing the moles of NH_3 and HCl.

Calculate the moles of NH_3 and NH_4^+ remaining after the reaction.

Use the Henderson-Hasselbalch equation: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{base}]}{[\text{acid}]} \right) \) to find the pH, where \( \text{pK}_a \) is related to the \( K_b \) of NH_3.

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Key Concepts

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

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant (a solution of known concentration) to a solution of the analyte (the solution of unknown concentration) until the reaction reaches its endpoint, which is often indicated by a color change or a pH change.

Buffer Solutions

Buffer solutions are mixtures that can resist changes in pH upon the addition of small amounts of acid or base. In the context of the titration of ammonia (NH3), which is a weak base, the solution can act as a buffer when it contains both the weak base and its conjugate acid (NH4+), allowing for a more stable pH during the titration process.

pH Calculation

The pH of a solution is a measure of its acidity or basicity, calculated as the negative logarithm of the hydrogen ion concentration. In titration problems, pH can be determined using the concentrations of the acid and base involved, the volume of titrant added, and the resulting equilibrium concentrations of the species present in the solution after the reaction has occurred.

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A 20.0-mL sample of 0.150 M KOH is titrated with 0.125 M HClO₄ solution. Calculate the pH after the following volumes of acid have been added: (d) 25.0 mL. (e) 30.0 mL.

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A 35.0-mL sample of 0.150 M acetic acid 1CH3COOH2 is titrated with 0.150 M NaOH solution. Calculate the pH after the following volumes of base have been added: (b) 17.5 mL.

Textbook Question

Consider the titration of 30.0 mL of 0.050 M NH₃ with 0.025 M HCl. Calculate the pH after the following volumes of titrant have been added: (e) 61.0 mL (f) 65.0 mL.

Textbook Question

Calculate the pH at the equivalence point for titrating 0.200 M solutions of each of the following bases with 0.200 M HBr: (a) sodium hydroxide (NaOH).

Textbook Question

Calculate the pH at the equivalence point for titrating 0.200 M solutions of each of the following bases with 0.200 M HBr: (b) hydroxylamine 1NH2OH2.

Consider the titration of 30.0 mL of 0.050 M NH3 with 0.025 M HCl. Calculate the pH after the following volumes of titrant have been added: (b) 20.0 mL (c) 59.0 mL.

Verified video answer for a similar problem:

Key Concepts

Titration

Buffer Solutions

pH Calculation

Consider the titration of 30.0 mL of 0.050 M NH₃ with 0.025 M HCl. Calculate the pH after the following volumes of titrant have been added: (b) 20.0 mL (c) 59.0 mL.