pH Calculator
Calculate pH, pOH and solution nature
pH Scale - Complete Guide
0-3: Strong Acid
HCl, H2SO4
4-6: Weak Acid
Vinegar, Lemon juice
7: Neutral
Pure water
8-11: Weak Base
Baking soda
12-14: Strong Base
NaOH, KOH
Formulas
pH = -log[H+]
pOH = -log[OH-]
pH + pOH = 14
[H+] = 10^(-pH)
Applications
- Chemistry: Acid-base titrations, buffer solutions
- Biology: Blood pH (7.35-7.45), enzyme activity
- Agriculture: Soil pH for crops
- Water treatment: Drinking water quality
Strong vs Weak Acids
Strong Acids (pH 0-2)
Completely dissociate in water
- HCl - Hydrochloric
- H2SO4 - Sulfuric
- HNO3 - Nitric
- HBr - Hydrobromic
Weak Acids (pH 3-6)
Partially dissociate in water
- CH3COOH - Acetic (Vinegar)
- H2CO3 - Carbonic
- H3PO4 - Phosphoric
- Citric acid
Buffer Solutions
Buffers resist pH changes when small amounts of acid or base are added:
- Acidic buffer: Weak acid + its salt (pH < 7)
- Basic buffer: Weak base + its salt (pH > 7)
- Blood: Maintains pH 7.35-7.45 using bicarbonate buffer
Henderson-Hasselbalch Equation
pH = pKa + log([A-]/[HA])
Used to calculate pH of buffer solutions
Solved Examples
Example 1: [H+] = 1x10^-5 M. Find pH.
pH = -log[1x10^-5] = -(-5) = 5
Answer: pH = 5 (Weak Acid)
Example 2: pH = 9. Find [H+].
[H+] = 10^-9 = 1x10^-9 M
Answer: [H+] = 1x10^-9 M (Weak Base)