Determining the pH of Magnesium Hydroxide Solution: A Comprehensive Guide

In this article, we will delve into the process of calculating the pH of a solution containing Mg(OH)? with a given concentration. Understanding this concept is crucial for anyone working with strong bases in chemistry or related fields. We will explore the necessary steps to determine the pH, including the dissociation of the compound and the calculation of relevant concentrations.

Understanding Magnesium Hydroxide and Its Dissociation

Magnesium hydroxide, Mg(OH)?, is a well-known strong base that dissociates completely in water. The dissociation reaction can be expressed as:

Mg(OH)? (aq) → Mg2? (aq) 2OH? (aq)

This dissociation means that when a mole of Mg(OH)? is dissolved in water, it produces one mole of Mg2? and two moles of OH?.

Calculating OH? Concentration

Given that the concentration of Mg(OH)? is 10?3 mol/dm3, we can determine the concentration of OH? using the stoichiometry of the dissociation reaction:

c(OH?) 2 x c(Mg(OH)?) 2 x 10?3 mol/dm3

This relationship is based on the understanding that every mole of Mg(OH)? produces two moles of OH? upon complete dissociation.

Calculating [H?] Concentration

The concentration of H? ions can be found using the water ion product constant, Kw, which is given by:

Kw [H?][OH?] 10?1? at 25°C

Substituting the known [OH?] concentration:

[H?] Kw / [OH?] 10?1? / (2 x 10?3) 0.5 x 10?11 M

Calculating pH

The pH of the solution can now be calculated using the -log[H?] relationship:

pH -log[H?] -log(0.5 x 10?11) ≈ 11.30

This value aligns with the theoretical pH calculation for a solution of strong base, where the [H?] is derived from the ion product of water.

Conclusion

The process of determining the pH of a magnesium hydroxide solution involves a careful understanding of its dissociation behavior and the use of the water ion product constant. This article aims to provide a clear and comprehensive guide to the steps involved, ensuring that students and professionals alike can confidently calculate the pH of similar solutions.

For further exploration into related topics, such as the behavior of strong bases and the effects of pH on various chemical systems, additional resources and studies can be found in the literature and online.