Chapter 17: Problem 13
What is the pH of a 0.0015 M solution of \(\mathrm{Ba}(\mathrm{OH})_{2} ?\)
Short Answer
Expert verified
The pH of a 0.0015 M \(\mathrm{Ba(OH)}_2\) solution is 11.48.
Step by step solution
01
Determine the Dissociation of the Base
Barium hydroxide, \(\mathrm{Ba(OH)}_2\), is a strong base that dissociates completely in water. The dissociation can be represented by the equation:\[ \mathrm{Ba(OH)}_2 (aq) \rightarrow \mathrm{Ba}^{2+} (aq) + 2\mathrm{OH}^- (aq) \]Since each molecule of \(\mathrm{Ba(OH)}_2\) releases two hydroxide ions \((\mathrm{OH}^-)\), we need to account for that in our calculations.
02
Calculate Hydroxide Ion Concentration
Since each molecule of \(\mathrm{Ba(OH)}_2\) dissociates to produce two \(\mathrm{OH}^-\) ions, the concentration of \(\mathrm{OH}^-\) ions in the solution is twice the concentration of \(\mathrm{Ba(OH)}_2\). Therefore, the hydroxide ion concentration is:\[ \text{[OH}^-\text{]} = 2 \times 0.0015 \, \text{M} = 0.0030 \, \text{M} \]
03
Calculate pOH
The \(\text{pOH}\) of a solution is calculated using the formula: \[ \text{pOH} = -\log_{10}[\text{OH}^-] \]Substitute \([\text{OH}^-]\) with the value found in Step 2:\[ \text{pOH} = -\log_{10}(0.0030) \approx 2.52 \]
04
Calculate pH from pOH
The \(\text{pH}\) and \(\text{pOH}\) are related by the equation: \[ \text{pH} + \text{pOH} = 14 \]Using the \(\text{pOH}\) value calculated in Step 3, find \(\text{pH}\):\[ \text{pH} = 14 - 2.52 = 11.48 \]
05
Conclusion
The pH of a 0.0015 M solution of \(\mathrm{Ba(OH)}_2\) is 11.48.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Strong Base
Barium hydroxide, or \(\mathrm{Ba(OH)}_2\), is classified as a strong base. This means it dissociates completely in water. When \(\mathrm{Ba(OH)}_2\) dissolves, every molecule separates into its ions completely:
This full dissociation is a key trait of strong bases as it ensures a higher availability of hydroxide ions in the solution, directly influencing the solution's pH.
- Barium ions \((\mathrm{Ba}^{2+})\)
- Hydroxide ions \((\mathrm{OH}^-)\)
This full dissociation is a key trait of strong bases as it ensures a higher availability of hydroxide ions in the solution, directly influencing the solution's pH.
Hydroxide Ion Concentration
In solutions of strong bases, the concentration of hydroxide ions \((\mathrm{OH}^-)\) can be calculated directly from the base's formula. For \(\mathrm{Ba(OH)}_2\):
Each molecule yields two hydroxide ions. If the solution concentration is \(0.0015\, \text{M}\), then:
This doubling is specific to compounds that release more than one hydroxide ion per molecule.
Each molecule yields two hydroxide ions. If the solution concentration is \(0.0015\, \text{M}\), then:
- The hydroxide ion concentration \([\text{OH}^-]\) is \(2 \times 0.0015\, \text{M} = 0.0030\, \text{M}\)
This doubling is specific to compounds that release more than one hydroxide ion per molecule.
pOH
The pOH is a measure of the concentration of hydroxide ions in a solution. It is calculated with the formula: \[ \text{pOH} = -\log_{10}[\text{OH}^-] \]
For our \(\mathrm{Ba(OH)}_2\) solution:
This low pOH value indicates a basic solution. The more hydroxide present, the lower the pOH.
For our \(\mathrm{Ba(OH)}_2\) solution:
- Substituting the hydroxide concentration: \(\text{pOH} = -\log_{10}(0.0030) \approx 2.52\)
This low pOH value indicates a basic solution. The more hydroxide present, the lower the pOH.
Water Dissociation
In water, pH and pOH are interconnected because of water's natural equilibrium. The equation:
shows this relationship. Water naturally dissociates to form \(\text{H}^+\) and \(\text{OH}^-\), and this constant relationship holds for any aqueous solution.
By knowing the pOH, you can easily find the pH. For example, if \(\text{pOH} = 2.52\), then:
This basic pH confirms the alkaline nature of a \(\mathrm{Ba(OH)}_2\) solution.
- \( \text{pH} + \text{pOH} = 14 \)
shows this relationship. Water naturally dissociates to form \(\text{H}^+\) and \(\text{OH}^-\), and this constant relationship holds for any aqueous solution.
By knowing the pOH, you can easily find the pH. For example, if \(\text{pOH} = 2.52\), then:
- \( \text{pH} = 14 - 2.52 = 11.48 \)
This basic pH confirms the alkaline nature of a \(\mathrm{Ba(OH)}_2\) solution.