pH Calculator

Calculate pH, pOH, [H⁺], [OH⁻] | Acid-Base Chemistry Tool

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pH
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pOH
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[H⁺] (mol/L)
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[OH⁻] (mol/L)
📝 Step-by-step solution
Enter a value and click calculate

📖 How to Use This pH Calculator

1
Select calculation mode - Choose from pH, [H⁺], pOH, or [OH⁻] as your starting value.
2
Enter your value - Input the known value (pH between 0-14, or concentration in mol/L).
3
Click "Calculate" - Get all four values (pH, pOH, [H⁺], [OH⁻]) with step-by-step solutions.

🧪 Understanding pH Scale

The pH scale measures how acidic or basic a solution is, ranging from 0 to 14 at 25°C.

📊 Key Formulas

pH = -log₁₀[H⁺]
pOH = -log₁₀[OH⁻]
pH + pOH = 14
[H⁺] = 10⁻ᵖᴴ
[OH⁻] = 10⁻ᵖᴼᴴ

🔬 Common pH Values

❓ Frequently Asked Questions

What does pH stand for?
pH stands for "potential of hydrogen" or "power of hydrogen." It measures the concentration of hydrogen ions (H⁺) in a solution.
Why does pH + pOH always equal 14?
At 25°C, the ion product of water (Kw) equals 1.0 × 10⁻¹⁴. Taking -log of both sides gives pH + pOH = 14.
Can pH be negative or greater than 14?
Yes, extremely concentrated strong acids can have pH below 0, and concentrated bases above 14. However, the standard pH scale (0-14) covers most practical applications.
How does temperature affect pH?
pH changes with temperature because Kw changes. At 25°C, Kw = 1×10⁻¹⁴. At 50°C, neutral pH = 6.63. This calculator assumes 25°C.