What is pH?
pH is a measure of the acidity or basicity of a solution, expressed on a scale of 0-14. A pH of 7 is neutral (like pure water), values below 7 are acidic, and values above 7 are basic (alkaline). pH stands for "power of Hydrogen" and is calculated as the negative logarithm of the hydrogen ion concentration. The pH concept is essential in chemistry, biology, medicine, agriculture, and industry.
pH Formula
pH = -log[H⁺]Formula: pOH = -log[OH⁻] | pH + pOH = 14Variables:
- pHAcidity measure (0-14)Acidity measure (0-14)(e.g.: pH = 3 (strong acid))
- [H⁺]Hydrogen ion concentration (M)Hydrogen ion concentration (M)(e.g.: [H⁺] = 10⁻³ M)
- [OH⁻]Hydroxide ion concentration (M)Hydroxide ion concentration (M)(e.g.: [OH⁻] = 10⁻¹¹ M)
- pOHBasicity measureBasicity measure(e.g.: pOH = 11)
Categories:
pH 0-3Strong acid (HCl, H₂SO₄)
pH 4-6Weak acid (vinegar, citrus)
pH 7Neutral (pure water)
pH 8-14Base (soap, bleach)
How to Use the KalkuLab pH Calculator
- 1
Select Mode
Choose whether to find pH from [H⁺] or [H⁺] from pH.
- 2
Enter Values
Enter H⁺ concentration (in molar) or the pH value.
- 3
Calculate
The system calculates the unknown value automatically.
- 4
Interpret Results
See whether the solution is acidic, neutral, or basic.
Examples
pH of HCl Solution
Problem:
Calculate the pH of 0.001 M HCl solution.
Solution:
- 1.[H⁺] = 0.001 = 10⁻³ M
- 2.pH = -log(10⁻³) = 3
Result:pH = 3
The solution is acidic.
Concentration from pH
Problem:
What is [H⁺] if pH = 5?
Solution:
- 1.[H⁺] = 10^(-pH)
- 2.[H⁺] = 10⁻⁵ M
Result:[H⁺] = 0.00001 M
The hydrogen ion concentration is 10⁻⁵ molar.
Frequently Asked Questions
Why is the pH scale from 0 to 14?
This scale covers [H⁺] concentrations from 10⁰ to 10⁻¹⁴ M, the practical range for most solutions. pH can actually be negative or greater than 14 for very concentrated solutions.
What is a buffer solution?
A buffer is a solution that resists pH change when small amounts of acid or base are added. Example: human blood (pH 7.4) uses a bicarbonate buffer system.
What is the pH of rainwater?
Normal rainwater is about pH 5.6 (slightly acidic due to CO₂). Acid rain has pH below 5.6 from SO₂ and NOₓ pollution.