Textbook Question
A 20.0-mL sample of 0.200 M HBr solution is titrated with 0.200 M NaOH solution. Calculate the pH of the solution after the following volumes of base have been added:
(a) 15.0 mL
(b) 19.9 mL.
Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 44a,b
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: (a) 20.0 mL. (b) 23.0 mL.
Verified step by step guidance1
Determine the initial moles of KOH in the solution using the formula: \( \text{moles} = \text{concentration} \times \text{volume} \). For KOH, use 0.150 M and 20.0 mL (convert mL to L by dividing by 1000).
Calculate the moles of HClO4 added for each volume using the same formula: \( \text{moles} = \text{concentration} \times \text{volume} \). Use 0.125 M for HClO4 and convert the given volumes (20.0 mL and 23.0 mL) to liters.
For part (a), compare the moles of KOH and HClO4. Since they react in a 1:1 ratio, determine if there is any excess reactant. If KOH is in excess, calculate the moles of KOH remaining and find the concentration of OH⁻ ions to determine the pOH, then convert to pH.
For part (b), again compare the moles of KOH and HClO4. If HClO4 is in excess, calculate the moles of HClO4 remaining and find the concentration of H⁺ ions to determine the pH directly.
Remember to adjust the total volume of the solution when calculating concentrations after the reaction, as the volume changes with the addition of HClO4. Use the formula: \( \text{concentration} = \frac{\text{moles}}{\text{total volume in L}} \).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Neutralization
Acid-base neutralization is a chemical reaction where an acid reacts with a base to produce water and a salt. In this case, KOH (a strong base) reacts with HClO4 (a strong acid) to form water and potassium perchlorate. Understanding this concept is crucial for determining the resulting pH after specific volumes of acid are added to the base.
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Lewis Acids and Bases
Molarity and Dilution
Molarity is a measure of concentration defined as moles of solute per liter of solution. In titration problems, calculating the moles of acid and base involved is essential to determine the point of neutralization and the resulting pH. Additionally, dilution effects must be considered when volumes of solutions are mixed, as they can alter the final concentration of the reactants.
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pH Calculation
pH is a logarithmic scale used to specify the acidity or basicity of a solution, calculated as the negative logarithm of the hydrogen ion concentration. After the neutralization reaction, the pH can be determined based on the remaining concentrations of H+ and OH- ions. Understanding how to calculate pH in different scenarios, such as before and after neutralization, is essential for solving the titration problem.
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Related Practice
Textbook Question
A 20.0-mL sample of 0.200 M HBr solution is titrated with 0.200 M NaOH solution. Calculate the pH of the solution after the following volumes of base have been added:
(c) 20.0 mL.
Textbook Question
A 20.0-mL sample of 0.200 M HBr solution is titrated with 0.200 M NaOH solution. Calculate the pH of the solution after the following volumes of base have been added: (e) 35.0 mL.
Textbook Question
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: (c) 24.0 mL.
Textbook Question
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.
Textbook Question
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.