The pH value of a calcium hydroxide solution depends on its concentration. A saturated solution of calcium hydroxide in pure water has a pH of about 12.4 at 25°C. When calcium hydroxide, Ca(OH)2, dissolves in water, it dissociates into Ca2+ and 2OH- ions, increasing the concentration of hydroxide ions in the solution.
Understanding the pH of Calcium Hydroxide in Water
Calculating the pH of Calcium Hydroxide Solutions
The pH of a calcium hydroxide solution can be calculated using the formula pH = 14 – pOH, where pOH is the negative logarithm of the hydroxide ion concentration. For example, for a calcium hydroxide solution with a concentration of 0.05 mol/dm3, the pOH would be 1.0, and the pH would be 13.09.
| Concentration of Ca(OH)2 | pH |
|---|---|
| Saturated solution | 12.4 |
| 0.05 mol/dm3 | 13.09 |
Factors Affecting the pH of Calcium Hydroxide Solutions
Calcium hydroxide is a highly alkaline substance, and its pH value can be influenced by the presence of other substances in the solution. For instance, when calcium hydroxide is mixed with different vehicles for use as an intracanal medicament, the pH of the mixture is affected by the pH of the vehicle.
Chlorhexidine, which has a low surface tension and an acidic pH, is found to be a better vehicle for calcium hydroxide when used as an intracanal medicament, as it results in a lower surface tension and a higher pH of the mixture.
Contaminants or impurities in the calcium hydroxide solution can also affect its pH value. For example, the presence of carbonate in a calcium hydroxide solution can cause concern, as it can lead to the formation of insoluble calcium carbonate, which can affect the pH of the solution.
Reproducibility of Calcium Hydroxide pH
Despite these factors, a saturated solution of calcium hydroxide is found to be reproducible within 1% and can serve as a pH standard over a considerable range of temperature.
Conclusion
In summary, the pH value of a calcium hydroxide solution depends on its concentration and the presence of other substances or impurities in the solution. A saturated solution of calcium hydroxide in pure water has a pH of about 12.4 at 25°C, and the pH of a calcium hydroxide solution with a concentration of 0.05 mol/dm3 is 13.09. Chlorhexidine is found to be a better vehicle for calcium hydroxide when used as an intracanal medicament, as it results in a lower surface tension and a higher pH of the mixture. Contaminants or impurities in the calcium hydroxide solution can affect its pH value, but a saturated solution of calcium hydroxide can serve as a pH standard over a considerable range of temperature.
References:
– https://pubmed.ncbi.nlm.nih.gov/19336854/
– https://nvlpubs.nist.gov/nistpubs/jres/56/jresv56n6p305_A1b.pdf
– https://www.sciencedirect.com/topics/chemistry/calcium-hydroxide
– https://www.echemi.com/community/what-is-the-ph-value-for-calcium-hydroxide-ca-oh-2-with-concentration-of-0-05-mol-dm-3-ph-poh-14_mjart2204103925_993.html
– https://www.youtube.com/watch?v=0b-KPe059y0