pH Calculator
Enter as decimal or exponential form (1e-3 for 10⁻³)
What is pH?
The pH value is a measure of the concentration of hydrogen ions (H⁺) in a solution. The abbreviation "pH" stands for "potentia hydrogenii" (power of hydrogen).
0
7
14
Acidic ← Neutral → Basic
- pH < 7: Acidic
- pH = 7: Neutral
- pH > 7: Basic
Formulas
pH Definition:
pH = -log₁₀[H⁺]
pH = -log₁₀[H⁺]
pOH Definition:
pOH = -log₁₀[OH⁻]
pOH = -log₁₀[OH⁻]
Inverse Formula:
[H⁺] = 10-pH
[H⁺] = 10-pH
Ion Product of Water (25°C):
pH + pOH = 14
pH + pOH = 14
Examples
Hydrochloric Acid
[H⁺] = 0.1 mol/L → pH = 1
[H⁺] = 0.1 mol/L → pH = 1
Vinegar
pH ≈ 2.5
pH ≈ 2.5
Pure Water
pH ≈ 7 (neutral)
pH ≈ 7 (neutral)
Ammonia Solution
pH ≈ 11
pH ≈ 11
Sodium Hydroxide (NaOH)
[OH⁻] = 0.1 mol/L → pOH = 1 → pH = 13
[OH⁻] = 0.1 mol/L → pOH = 1 → pH = 13
Technical Background
Ion Product of Water
At 25°C, the ion product of water in aqueous solutions is:
Kw = [H⁺] · [OH⁻] = 10-14
This means the sum of pH and pOH always equals 14.
Practical Applications
- Laboratory Chemistry: pH determination by titration and pH meters
- Environmental Protection: Monitoring water bodies and soil pH
- Food Industry: Control of acidity and basicity
- Medicine: pH control of blood and urine tests
- Buffer Chemistry: Stabilizing pH in biochemical systems
Common pH Values in Everyday Life
| Substance | pH Value | Classification |
|---|---|---|
| Stomach Acid | 1–2 | Strongly acidic |
| Lemon Juice | 2–3 | Acidic |
| Vinegar | 2.5–3.5 | Acidic |
| Tomato | 4–4.5 | Weakly acidic |
| Distilled Water | 7 | Neutral |
| Blood | 7.35–7.45 | Slightly basic |
| Seawater | 8–8.3 | Basic |
| Ammonia Solution | 11–12 | Strongly basic |
| Sodium Hydroxide (NaOH) | 13–14 | Strongly basic |
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