pH Scale Chart
Explore the spectrum of Acidity and Alkalinity. From Battery Acid to Drain Cleaner, understand the chemistry of everyday substances.
Interactive pH Spectrum
Battery Acid
High concentration of Hydrogen ions.
Stomach Acid
High concentration of Hydrogen ions.
Lemon Juice, Vinegar
High concentration of Hydrogen ions.
Orange Juice, Soda
High concentration of Hydrogen ions.
Tomato Juice
High concentration of Hydrogen ions.
Black Coffee
High concentration of Hydrogen ions.
Urine, Milk
High concentration of Hydrogen ions.
Pure Water
Perfectly balanced ions.
Seawater, Eggs
High concentration of Hydroxide ions.
Baking Soda
High concentration of Hydroxide ions.
Milk of Magnesia
High concentration of Hydroxide ions.
Ammonia
High concentration of Hydroxide ions.
Soapy Water
High concentration of Hydroxide ions.
Bleach
High concentration of Hydroxide ions.
Liquid Drain Cleaner
High concentration of Hydroxide ions.
The Power of Ten: Understanding the Scale
The "p" in pH stands for potenz (German for power). The scale is not linear like a ruler—it is Logarithmic.
The 10x Rule
A jump of just 1 pH unit represents a 10-fold change in acidity.
pH 4 is 10x more acidic than pH 5.
pH 3 is 100x more acidic than pH 5.
pH 2 is 1000x more acidic than pH 5.
This explains why "slightly acidic" rain (pH 5.6) is harmless, but "acid rain" (pH 4.0) can destroy forests—it's nearly 50 times more acidic!
The Battle of Ions: H⁺ vs OH⁻
Acidic Dominance
Acids donate Hydrogen ions (H⁺). The more H⁺ swimming around, the lower the pH.
Basic Dominance
Bases accept H⁺ or donate Hydroxide ions (OH⁻). pOH is the measure of OH⁻.
How Do We Measure It?
While modern labs use digital meters, the classic method uses Indicators—chemicals that change color based on protonation state.
- Litmus PaperRed in Acid, Blue in Base.
- PhenolphthaleinColorless in Acid, Pink in Base.
- Universal IndicatorFull spectrum change (used in our chart above).
Math Cheat Sheet
Buffers in Action
Your body cannot survive if blood pH deviates even slightly from 7.4.
H₂CO₃ ⇌ HCO₃⁻ + H⁺
If acid increases, Bicarbonate absorbs it. If base increases, Carbonic acid neutralizes it.
Frequently Asked Questions
What does "logarithmic scale" mean for pH?
The pH scale is base-10 logarithmic. This means that a pH of 3 is 10 times more acidic than a pH of 4, and 100 times more acidic than a pH of 5.
What is pOH?
pOH measures the concentration of Hydroxide ions (OH⁻). It is the opposite of pH. At 25°C, pH + pOH = 14. A low pOH means a solution is basic.
Why is rain naturally acidic?
Normal rain has a pH around 5.6 because it absorbs carbon dioxide from the air, forming weak carbonic acid. "Acid rain" has a much lower pH (around 4.0) due to pollution.
What is a buffer solution?
A buffer is a solution that resists changes in pH when small amounts of acid or base are added. Human blood is a buffer, keeping pH strictly between 7.35 and 7.45.
How do Universal Indicators work?
Universal Indicators are mixtures of dyes that change color across the entire pH spectrum—typically Red for strong acids, Green for neutral, and Purple for strong bases.
Can pH be less than 0 or greater than 14?
Yes! Extremely concentrated acids (like 10M HCl) can have a negative pH, and concentrated bases can have a pH above 14. However, the 0-14 scale covers almost all common scenarios.
Why is distilled water pH 7?
In pure water, a tiny fraction of molecules dissociate into equal numbers of H⁺ and OH⁻ ions (10⁻⁷ M each). The negative log of 10⁻⁷ is 7.
Is milk acidic or basic?
Milk is slightly acidic with a pH of around 6.5-6.7, due to the presence of lactic acid.
What is the pH of human stomach acid?
Stomach acid is highly acidic, typically between pH 1.5 and 3.5. This helps break down food and kill bacteria.
How does temperature affect pH?
The pH of neutral water decreases as temperature increases (e.g., pH 6.14 at 100°C) because more water molecules dissociate. However, it remains chemically neutral because [H⁺] still equals [OH⁻].