pOH
Basicity from hydroxide-ion concentration.
Formula
Variables
Example
pH + pOH = 14
How it works
The pOH scale is a convenient way to express how much hydroxide ion, OH B7 b, is present in a solution using a logarithm. Because hydroxide concentrations can vary over many powers of ten, taking log10 turns those tiny concentrations into easier-to-handle numbers. A lower pOH means more OH b7 b and therefore a more basic solution, while a higher pOH means less OH b7 b and a less basic one.
When to use it
Use this when you are given the hydroxide-ion concentration of a solution and need to find its pOH. It is also useful when comparing how basic two solutions are or when working with pH-pOH relationships in acid-base problems.
Worked example, step by step
Given: [OH b7] = 3.2 d7 10^-5 M Step 1: Write the formula: pOH = -log10[OH b7] Step 2: Substitute the value: pOH = -log10(3.2 d7 10^-5) Step 3: Evaluate the logarithm: log10(3.2 d7 10^-5) 3d log10(3.2) + log10(10^-5) Step 4: Use the values: log10(3.2) b9 0.51 and log10(10^-5) = -5 Step 5: Add them: log10(3.2 d7 10^-5) b9 0.51 + (-5) = -4.49 Step 6: Apply the negative sign: pOH = -(-4.49) = 4.49 Final answer: pOH b9 4.49
Common mistakes to avoid
- Forgetting the negative sign in pOH = -log10[OH^-]
- Using concentration units incorrectly instead of the numerical molarity value
- Confusing pOH with pH or assuming a higher pOH means a more basic solution
Did You Know?
pH and pOH always add up to 14 in water at room temperature.
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