The pH of an acid is always below 7.0.
Acidity and alkalinity are measured using the pH scale. This scale runs from 0 to 14 and indicates the concentration of hydrogen ions (H⁺) in a solution. A higher concentration of H⁺ ions means a lower pH and greater acidity.
Understanding the pH Scale
The pH scale is a fundamental concept in chemistry used to classify aqueous solutions. According to the pH scale:
- Below 7.0 is acidic.
- Exactly 7.0 is neutral.
- Above 7.0 is alkaline (basic).
This means any substance with a pH value less than 7.0 is considered an acid. The lower the pH value (e.g., pH 2 or pH 3), the stronger the acid. Conversely, a pH value close to 7.0 (e.g., pH 6) indicates a weaker acid.
The pH Spectrum
Here's a simple breakdown of the pH scale:
| pH Value Range | Classification | Characteristics |
|---|---|---|
| 0 - < 7.0 | Acidic | High concentration of H⁺ ions |
| 7.0 | Neutral | Balanced H⁺ and OH⁻ ions |
| > 7.0 - 14 | Alkaline/Basic | High concentration of OH⁻ ions (or low H⁺) |
Examples of Acidic Substances
You encounter many acidic substances in your daily life. Their pH values fall somewhere below 7.0 on the scale.
- Lemon juice (typically pH 2)
- Vinegar (typically pH 2.5 - 3.0)
- Coffee (typically pH 4.5 - 5.0)
- Rainwater (slightly acidic, typically pH 5.6)
- Stomach acid (very acidic, typically pH 1.5 - 3.5)
Understanding the pH helps determine how a substance might react chemically and its potential effects on living organisms or materials.
