1. What is pH and Hydrogen Ion Concentration?

pH is a logarithmic scale used to specify the acidity or basicity of an aqueous solution. The hydrogen ion concentration [H⁺] represents the molar concentration of hydrogen ions in a solution, which directly determines its acidity.

2. How to Calculate [H⁺] Without a Calculator

The fundamental relationship between pH and hydrogen ion concentration is:

To calculate this without a calculator:

• For integer pH values: [H⁺] = 1 × 10^{-pH}
• For pH = 7: [H⁺] = 1 × 10^{-7} mol/L (neutral)
• For pH values with one decimal place: use approximation methods
• Remember that each whole pH unit represents a 10-fold change in [H⁺]

Example: For pH = 3.5, [H⁺] ≈ 3.16 × 10^{-4} mol/L (between 10^{-3} and 10^{-4})

3. Understanding the pH Scale

Details: The pH scale ranges from 0 to 14, with 7 being neutral. Values below 7 indicate acidity, while values above 7 indicate basicity. The scale is logarithmic, meaning each whole number change represents a tenfold change in hydrogen ion concentration.

4. Using the Calculator

Tips: Enter the pH value (0-14) to calculate the corresponding hydrogen ion concentration. The result will be displayed in moles per liter (mol/L).

5. Frequently Asked Questions (FAQ)

Q1: What does a pH of 7 mean?
A: A pH of 7 indicates a neutral solution where [H⁺] = [OH⁻] = 1 × 10^{-7} mol/L.

Q2: How does pH relate to acidity?
A: Lower pH values indicate higher acidity and higher hydrogen ion concentrations. Each 1-unit decrease in pH means a 10-fold increase in [H⁺].

Q3: Can I estimate [H⁺] for non-integer pH values?
A: Yes, you can approximate using the nearest integer values. For example, pH 5.3 is closer to 5 than 6, so [H⁺] is slightly less than 10^{-5} mol/L.

Q4: What is the [H⁺] for common substances?
A: Lemon juice (pH ~2.4): [H⁺] ~4 × 10^{-3} mol/L; Pure water (pH 7): [H⁺] = 1 × 10^{-7} mol/L; Baking soda (pH ~8.3): [H⁺] ~5 × 10^{-9} mol/L.

Q5: Why is the pH scale logarithmic?
A: The logarithmic scale allows us to represent the enormous range of hydrogen ion concentrations (from ~1 mol/L to 10^{-14} mol/L) using a manageable 0-14 scale.