pH Calculator
Calculate pH, pOH, and ion concentrations for acid-base chemistry solutions
Calculate pH & pOH
How to Use
Calculate from pH
Enter a pH value to find pOH and ion concentrations. pH measures hydrogen ion concentration in a solution.
pH Scale
- 0-6.9: Acidic (more H⁺ ions)
- 7.0: Neutral (equal H⁺ and OH⁻)
- 7.1-14: Basic/Alkaline (more OH⁻ ions)
Common pH Values
- Battery acid: 0-1
- Lemon juice: 2
- Coffee: 5
- Pure water: 7
- Baking soda: 9
- Household ammonia: 11
Try Sample Calculation
Click “Load Sample” to see a typical calculation for the selected input type.
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How to Use the pH Calculator
Getting Started
- Step 1: Select the calculation type based on your known value
- Step 2: Enter the known pH, pOH, [H+], or [OH-] concentration
- Step 3: Click Calculate to get all related values
- Step 4: Review the acid/base classification and calculations
Key Acid-Base Concepts
- pH Scale: Ranges from 0-14, measures hydrogen ion concentration
- pOH Scale: Measures hydroxide ion concentration, pH + pOH = 14
- Neutral Solutions: pH = 7, [H+] = [OH-] = 1 × 10⁻⁷ M
- Logarithmic Scale: Each pH unit represents 10x concentration change
Laboratory Applications
- Buffer Preparation: Henderson-Hasselbalch equation calculations
- Titration Analysis: Endpoint determination and curve analysis
- Quality Control: Water treatment and pharmaceutical testing
- Biochemistry: Enzyme activity and protein stability studies
Safety and Best Practices
- pH Meter Calibration: Use standard buffer solutions (pH 4, 7, 10)
- Temperature Effects: pH changes with temperature, standardize conditions
- Electrode Care: Store in KCl solution, avoid contamination
- Safety Protocols: Handle acids/bases with proper PPE
Frequently Asked Questions
Why is the pH scale logarithmic?
The pH scale is logarithmic because hydrogen ion concentrations vary over many orders of magnitude (10⁻¹⁴ to 10⁰ M). pH = -log[H+] compresses this range into a manageable 0-14 scale.
How do I calculate buffer pH using Henderson-Hasselbalch?
pH = pKa + log([A⁻]/[HA]), where pKa is the acid dissociation constant, [A⁻] is conjugate base concentration, and [HA] is weak acid concentration.
What's the difference between strong and weak acids/bases?
Strong acids/bases completely ionize in solution (HCl, NaOH). Weak acids/bases partially ionize (acetic acid, ammonia). This affects pH calculations significantly.
How does temperature affect pH measurements?
Pure water's pH changes from 7.47 at 0°C to 6.14 at 100°C. Most measurements are standardized at 25°C. Temperature also affects electrode response and buffer stability.
When should I use pH vs pOH calculations?
Use pH for acidic solutions (pH < 7) and pOH for basic solutions (pH > 7). Both are equivalent since pH + pOH = 14, but one may be more convenient.
How accurate should my pH measurements be?
For most applications, ±0.1 pH units is sufficient. Analytical work may require ±0.01 pH units. Use calibrated meters and fresh buffers for best accuracy.
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