Calculate Ph for Oh 1.0 10-5 M

The pH of a solution can be calculated from its hydroxide (OH⁻) concentration using the pH = 14 - pOH formula. This calculator provides an easy way to determine the pH when you know the OH⁻ concentration in moles per liter (M).

How to Calculate pH from OH⁻ Concentration

To calculate the pH of a solution when you know the hydroxide concentration (OH⁻), follow these steps:

Determine the hydroxide concentration in moles per liter (M).
Calculate the pOH using the formula: pOH = -log₁₀[OH⁻].
Use the relationship between pH and pOH: pH = 14 - pOH.

This method works for aqueous solutions at standard temperature (25°C) where water autoionization is assumed to be 1.0 × 10⁻¹⁴ M.

Key Formula

pH = 14 - pOH

pOH = -log₁₀[OH⁻]

The pH Calculation Formula

The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration:

pH = -log₁₀[H⁺]

For aqueous solutions, the product of hydrogen ion and hydroxide ion concentrations is constant:

[H⁺][OH⁻] = 1.0 × 10⁻¹⁴ M² (at 25°C)

Taking the negative logarithm of both sides gives the relationship between pH and pOH:

pH + pOH = 14

Therefore, pH = 14 - pOH

Example Calculation

Let's calculate the pH for a solution with an OH⁻ concentration of 1.0 × 10⁻⁵ M:

Given: [OH⁻] = 1.0 × 10⁻⁵ M
Calculate pOH: pOH = -log₁₀(1.0 × 10⁻⁵) = 5
Calculate pH: pH = 14 - pOH = 14 - 5 = 9

The pH of this solution is 9.

Important Note

This calculation assumes standard temperature (25°C) and that the solution is sufficiently dilute that activity coefficients can be approximated as 1.

Interpreting the pH Result

A pH of 9 indicates that the solution is basic. Here's what this means:

The hydrogen ion concentration is 1.0 × 10⁻⁵ M
The hydroxide ion concentration is 1.0 × 10⁻⁵ M
The solution is 100,000 times more basic than neutral (pH 7)

Solutions with pH values between 7 and 14 are considered basic, with higher pH values indicating stronger bases.

Frequently Asked Questions

What is the relationship between pH and pOH?: The sum of pH and pOH is always 14 for aqueous solutions at standard temperature (25°C). This is derived from the water autoionization constant.
Can I use this formula for any temperature?: No, this formula assumes standard temperature (25°C). At different temperatures, the water autoionization constant changes, and a temperature correction factor would be needed.
What if my solution is very concentrated?: For concentrated solutions, activity coefficients become important and should be considered. This calculator assumes dilute solutions where activity coefficients are approximately 1.
How accurate is this calculation?: This calculator provides accurate results for dilute aqueous solutions at standard temperature, with typical laboratory precision.
What does a pH of 9 mean in practical terms?: A pH of 9 means the solution is strongly basic and would feel slippery to the skin, would react with acids, and would have a strong alkaline taste.