🧪pH vs pOH🧪
pH and pOH are complementary scales describing the same solution. Understanding their link makes acid-base calculations far quicker.
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🧪pH
- ✓Measures H+ ion concentration
- ✓pH = -log[H+]
- ✓Lower value means more acidic
- ✓Most commonly reported scale
- ✓Range 0-14 in water at 25°C
🧪pOH
- ✓Measures OH- ion concentration
- ✓pOH = -log[OH-]
- ✓Lower value means more basic
- ✓Useful for base calculations
- ✓Always equals 14 minus pH at 25°C
Verdict
pH and pOH describe the same equilibrium from opposite directions. Because pH + pOH = 14 in water at 25°C, knowing one instantly gives the other.
Frequently asked
Why do pH and pOH add to 14?+
Because water's ion product Kw is 1×10⁻¹⁴ at 25°C, so the logs of [H+] and [OH-] sum to 14.
Which is used more often?+
pH is far more common in labs and everyday use, but pOH simplifies many base-strength calculations.
Does the sum stay 14 at all temperatures?+
No. Kw changes with temperature, so the pH + pOH sum is only exactly 14 at 25°C.
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