Calcium Hydroxide pH: Understanding the Concentration and Dissociation

Calcium hydroxide, Ca(OH)2, is a well-known strong base that is commonly used in various industrial and laboratory applications. The concentration and dissociation of Ca(OH)2 in water significantly impact its pH value. In this article, we will explore the pH of different concentrations of Ca(OH)2 in aqueous solution.

Concentration and Dissociation of Calcium Hydroxide

Calcium hydroxide is a solute that does not disassociate extensively in water. At room temperature, the solubility of Ca(OH)2 is limited, with a maximum concentration of approximately 0.0025 M. However, for the purpose of understanding the impact of concentration on pH, let's consider different concentrations and their dissociation.

Calculation of pH for 0.50 M NaOH

Considering a more soluble base, sodium hydroxide (NaOH), let's take the concentration of 0.50 M. Sodium hydroxide is a strong base and completely dissociates in water:

NaOH → Na OH-

Thus, the concentration of OH- is 0.50 M. The pH can be calculated as follows:

[text{pOH} - log[text{OH}^-] - log(0.50) 0.30]

Using the relationship between pH and pOH:

[text{pH} text{pOH} 14]

[text{pH} 14 - text{pOH} 14 - 0.30 13.70]

Calculation of pH for 0.25 M Ca(OH)2

Note that the solubility of Ca(OH)2 is much lower than NaOH. At room temperature, a saturated solution of Ca(OH)2 has a concentration of about 0.0025 M. Assuming we have a 0.25 M solution of Ca(OH)2, we need to calculate its dissociation in water:

[text{Ca(OH)}_2 rightarrow text{Ca}^{2 } 2text{OH}^-]

Therefore, the concentration of OH- is 0.5 M (0.25 M x 2). The pOH can be calculated as:

[text{pOH} - log[text{OH}^-] - log(0.50) 0.30]

Using the relationship between pH and pOH again:

[text{pH} 14 - text{pOH} 14 - 0.30 13.70]

Calculation for a Saturated Solution of Ca(OH)2

For a saturated solution of Ca(OH)2, the concentration is approximately 0.0025 M. Let's calculate the pH for this concentration:

[text{Ca(OH)}_2 rightarrow text{Ca}^{2 } 2text{OH}^-]

Thus, the concentration of OH- is 0.005 M (0.0025 M x 2). The pOH can be calculated as:

[text{pOH} - log[text{OH}^-] - log(0.005) 2.30]

Using the relationship between pH and pOH:

[text{pH} 14 - text{pOH} 14 - 2.30 11.70]

Conclusion

The pH of a solution is directly related to the concentration of hydroxide ions (OH-). In this article, we have explored the pH of different concentrations of calcium hydroxide and sodium hydroxide in aqueous solutions. Understanding these calculations is crucial for various applications in chemistry and environmental science.

For further reading, you may want to explore the properties of other strong bases and their behavior in aqueous solutions.