Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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![**Question 3: Calculate the pH of a 0.100 M KCN solution.**
In this problem, you are asked to determine the pH of a potassium cyanide (KCN) solution at a concentration of 0.100 M.
**Steps for Calculation:**
1. **Understand the Chemistry:**
- KCN dissociates in water to form K⁺ and CN⁻ ions.
- The CN⁻ (cyanide) ion is a weak base and will react with water to form HCN and OH⁻.
2. **Chemical Equilibrium:**
- The reaction is: CN⁻ + H₂O ⇌ HCN + OH⁻
- Use the base dissociation constant (Kb) for CN⁻, which can be calculated from the known Ka of HCN (acid dissociation constant) using the relation:
\[
K_b = \frac{K_w}{K_a}
\]
where \(K_w\) is the ion-product constant of water (\(1.0 \times 10^{-14}\) at 25°C).
3. **Set up the ICE Table:**
- Initial concentrations, changes, and equilibrium concentrations are established.
- Calculate the concentration of OH⁻ at equilibrium.
4. **Calculate pOH and pH:**
- From the concentration of OH⁻, calculate the pOH:
\[
\text{pOH} = -\log[\text{OH}⁻]
\]
- Finally, convert pOH to pH:
\[
\text{pH} = 14 - \text{pOH}
\]
This solution concept is essential for understanding weak base behavior in aqueous solutions and calculating related pH values. Understanding these calculations deeply involves chemical equilibria, logarithmic conversions, and equilibrium constants.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F7fcffe20-88c0-46a7-a9a5-147a481f673b%2F74657efb-64b5-401f-bacd-044c16bf1279%2Fv5sg5f_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**Question 3: Calculate the pH of a 0.100 M KCN solution.**
In this problem, you are asked to determine the pH of a potassium cyanide (KCN) solution at a concentration of 0.100 M.
**Steps for Calculation:**
1. **Understand the Chemistry:**
- KCN dissociates in water to form K⁺ and CN⁻ ions.
- The CN⁻ (cyanide) ion is a weak base and will react with water to form HCN and OH⁻.
2. **Chemical Equilibrium:**
- The reaction is: CN⁻ + H₂O ⇌ HCN + OH⁻
- Use the base dissociation constant (Kb) for CN⁻, which can be calculated from the known Ka of HCN (acid dissociation constant) using the relation:
\[
K_b = \frac{K_w}{K_a}
\]
where \(K_w\) is the ion-product constant of water (\(1.0 \times 10^{-14}\) at 25°C).
3. **Set up the ICE Table:**
- Initial concentrations, changes, and equilibrium concentrations are established.
- Calculate the concentration of OH⁻ at equilibrium.
4. **Calculate pOH and pH:**
- From the concentration of OH⁻, calculate the pOH:
\[
\text{pOH} = -\log[\text{OH}⁻]
\]
- Finally, convert pOH to pH:
\[
\text{pH} = 14 - \text{pOH}
\]
This solution concept is essential for understanding weak base behavior in aqueous solutions and calculating related pH values. Understanding these calculations deeply involves chemical equilibria, logarithmic conversions, and equilibrium constants.
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