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Calculate Ph of 0.0092 M Al Oh 3

Reviewed by Calculator Editorial Team

Aluminum hydroxide (Al(OH)3) is a weak base that dissolves in water to form hydroxide ions. This calculator determines the pH of a 0.0092 M Al(OH)3 solution using standard chemical equilibrium principles.

How to Calculate pH of Al(OH)3

The pH of an aluminum hydroxide solution can be calculated using the following steps:

  1. Determine the concentration of Al(OH)3 in moles per liter (M)
  2. Calculate the equilibrium concentration of hydroxide ions (OH⁻)
  3. Convert the hydroxide ion concentration to pOH
  4. Calculate pH using the relationship between pH and pOH

Note: This calculation assumes ideal conditions and does not account for temperature effects or complexation reactions.

pH Calculation Formula

The pH of an Al(OH)3 solution is calculated using the following formula:

pH = 14 - pOH

where pOH = -log[OH⁻]

[OH⁻] = √(Ksp × [Al(OH)3])

Ksp = 1.8 × 10⁻⁵ (solubility product constant for Al(OH)3 at 25°C)

For a 0.0092 M Al(OH)3 solution:

[OH⁻] = √(1.8 × 10⁻⁵ × 0.0092) ≈ 0.0013 M

pOH = -log(0.0013) ≈ 2.88

pH = 14 - 2.88 ≈ 11.12

Worked Example

Let's calculate the pH of a 0.0092 M Al(OH)3 solution step by step:

  1. Given [Al(OH)3] = 0.0092 M
  2. Calculate [OH⁻] using Ksp = 1.8 × 10⁻⁵:
    [OH⁻] = √(1.8 × 10⁻⁵ × 0.0092) ≈ √(1.656 × 10⁻⁷) ≈ 0.0013 M
  3. Calculate pOH:
    pOH = -log(0.0013) ≈ 2.88
  4. Calculate pH:
    pH = 14 - 2.88 ≈ 11.12

The calculated pH of 11.12 indicates a basic solution, which is expected for aluminum hydroxide.

Interpreting the Result

A pH of 11.12 for a 0.0092 M Al(OH)3 solution indicates:

  • The solution is strongly basic
  • There is significant dissociation of Al(OH)3 into Al³⁺ and OH⁻ ions
  • The hydroxide ion concentration is 0.0013 M

Remember that pH measurements should be taken carefully, as aluminum hydroxide can form gels or precipitates that affect measurement accuracy.

FAQ

Why is the pH of Al(OH)3 higher than expected?

The high pH results from the dissociation of Al(OH)3 into Al³⁺ and OH⁻ ions, which increases the hydroxide ion concentration in solution.

Does temperature affect the pH calculation?

Yes, the solubility product constant (Ksp) for Al(OH)3 changes with temperature. This calculator uses the value at 25°C.

Can Al(OH)3 form precipitates in solution?

Yes, aluminum hydroxide can form gels or precipitates that may affect pH measurements and require special handling techniques.