The pH of Mg(OH)2 in Water

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The pH of a saturated solution of magnesium hydroxide (Mg(OH)2) in water is approximately 10.32. This is due to the hydroxide ions (OH-) that are released into the solution when Mg(OH)2 dissolves. The concentration of these hydroxide ions is related to the solubility product constant (Ksp) of Mg(OH)2, which is 1.0 x 10^-11.

Understanding the pH of Mg(OH)2 in Water

To calculate the pH at which Mg(OH)2 begins to precipitate from a solution containing Mg^(2+) ions, you can use the formula:

pH = 9 + 1/2 log([Mg^(2+)])

Where [Mg^(2+)] is the concentration of magnesium ions in the solution.

If the pH of the solution is below 9, Mg(OH)2 will not precipitate, and if the pH is above 9, Mg(OH)2 will begin to precipitate. The pH of the solution can be adjusted by adding an acid or a base. For example, if the pH is too high, you can add a strong acid such as hydrochloric acid (HCl) to lower the pH. Conversely, if the pH is too low, you can add a strong base such as sodium hydroxide (NaOH) to raise the pH.

Factors Affecting the pH of Mg(OH)2 in Water

PH of Mg(OH)2 in waterImage source: wikimedia

It’s worth noting that Mg(OH)2 is not a contaminant or a chemical substance itself, but rather a compound that can be formed when magnesium ions (Mg^(2+)) and hydroxide ions (OH-) are present in water. Contaminants or chemicals that can affect the pH of water include acids, bases, and salts. These can come from a variety of sources, such as industrial pollution, agricultural runoff, or natural geological formations.

Dealing with Contaminants or Chemicals

To deal with these contaminants or chemicals, you can use a variety of methods, such as chemical treatment, filtration, or ion exchange. For example, if the water is acidic, you can add a base such as lime (calcium hydroxide) to raise the pH. If the water is basic, you can add an acid such as sulfuric acid to lower the pH. Filtration can remove particulate matter that may be affecting the pH, and ion exchange can remove dissolved ions that may be contributing to the pH.

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Conclusion

In summary, the pH of a saturated solution of Mg(OH)2 in water is approximately 10.32. The pH can be adjusted by adding an acid or a base, and contaminants or chemicals that can affect the pH can be removed using a variety of methods.

References:

  1. Socratic.org. (2016). A saturated solution of Mg(OH)2 in water has pH = 10.32. Retrieved from https://socratic.org/chemistry/equilibrium/ksp-a-saturated-solution-of-mgoh2-in-water-has-ph-10-32
  2. Socratic.org. (2016). Calculate the pH at which Mg(OH)2 begins to precipitate from a solution containing 0.1 M Mg^(2+) ions? Ksp for Mg(OH)2 = 1.0 x 10^-11. Retrieved from https://socratic.org/questions/calculate-the-ph-at-which-mg-oh-2-begins-to-precipitate-from-a-solution-containi
  3. Wyzant. (2023). What is the solubility of Mg(OH)2 at a pH of 12.00? (Ksp Mg(OH)2 is 1.6 × 10⁻¹³). Retrieved from https://www.wyzant.com/resources/answers/918629/what-is-the-solubility-of-mg-oh-2-at-a-ph-of-12-00-ksp-mg-oh-is-1-6-x-10
  4. Physics Forums. (2010). Calculating pH for Mg(OH)2 Precipitation 0.1M Mg2+. Retrieved from https://www.physicsforums.com/threads/calculating-ph-for-mg-oh-2-precipitation-0-1m-mg2.431448/.