pH - Basic (alkaline) vs. Acidic
Introduction to pH - the acidic and basic (alkaline) definition.
pH can be viewed as an abbreviation for power of Hydrogen - or more completely, power of the concentration of the Hydrogen ionin a liquid.
The mathematical definition of pH is a bit less intuitive but in general more useful. It says that the pH is equal to to the negative logarithmic value of the Hydrogen ion (H+) concentration, or
pH = -log [H+]
pH can alternatively be defined mathematically as the negative logarithmic value of the Hydroxonium ion (H3O+) concentration. Using the Bronsted-Lowry approach
pH = -log [H3O+]
pH values are calculated in powers of 10. The hydrogen ion concentration in a solution with pH 1.0 is 10 times larger than the hydrogen concentration in a solution with pH 2.0. The larger the hydrogen ion concentration - the smaller the pH.
- when the pH is above 7 the solution is basic (alkaline)
- when the pH is below 7 the solution is acidic
In pure neutral water the concentration of hydrogen and hydroxide ions are both 10-7 equivalents per liter.
| pH | Ion Concentration (gram equivalent per liter) | Type of Solution |
|---|---|---|
| 0 | 1.0 | Acid Solution - Hydrogen ions - H+ |
| 1 | 0.1 | |
| 2 | 0.01 | |
| 3 | 0.001 | |
| 4 | 0.0001 | |
| 5 | 0.00001 | |
| 6 | 0.000001 | |
| 7 | 0.0000001 | Neutral Solution (pure neutral water) |
| 8 | 0.000001 | Basic (alkaline) Solution - Hydroxide ions - OH- |
| 9 | 0.00001 | |
| 10 | 0.0001 | |
| 11 | 0.001 | |
| 12 | 0.01 | |
| 13 | 0.1 | |
| 14 | 1.0 |
Download and print pH Ion Concentration Chart
Some common Products and their pH Values
pH values in some common products:
| Product | pH |
|---|---|
| Battery Acid | 0 |
| HCl in stomach acid | 1 |
| Lemon juice, vinegar | 2-3 |
| Orange juice | 3-4 |
| Acid rain | 4 |
| Black coffee | 5 |
| Urine, saliva | 6 |
| Pure water | 7 |
| Sea water | 8 |
| Baking soda | 9 |
| Ammonia solution | 10-11 |
| Soapy water | 12 |
| Bleach | 13 |
| Oven cleaner | 13-14 |
| Drain cleaner | 14 |
Acid-Base Indicators
| Indicator | pH - Range | Color Cange | |
|---|---|---|---|
| Acid | Base | ||
| Thymol blue | 1.2 - 2.8 | red | yellow |
| Pentamethoxy red | 1.2 - 2.3 | red - violet | colorless |
| Tropeolin | 1.3 - 3.2 | red | yellow |
| 2,4 - Dinitrophenol | 2.4 - 4.0 | colorless | yellow |
| Methyl yellow | 2.9 - 4.0 | red | yellow |
| Methyl orange | 3.1 - 4.4 | red | orange |
| Congo red | 3.0 - 4.2 | blue-violet | red-orange |
| Bromphenol blue | 3.0 - 4.6 | yellow | blue - violet |
| Tetrabromphenol blue | 3.0 - 4.6 | yellow | blue |
| Alizarin sodium sulfonate | 3.7 - 5.2 | yellow | violet |
| α - Naphthyl red | 3.7 - 5.0 | red | yellow |
| p - Ethoxychrysoidine | 3.5 - 5.5 | red | yellow |
| Bromcresol green | 4.0 - 5.6 | yellow | blue |
| Methyl red | 4.4 - 6.2 | red | yellow |
| Bromcresol purple | 5.2 - 6.8 | yellow | purple |
| Chlorphenol red | 5.4 - 6.8 | yellow | red |
| Bromphenol blue | 6.2 - 7.6 | yellow | blue |
| p - Nitrophenol | 5.0 - 7.0 | colorless | yellow |
| Litmus | 5.0 - 8.0 | red | blue |
| Azolitmin | 5.0 - 8.0 | red | blue |
| Phenol red | 6.4 - 8.0 | yellow | red |
| Neutral red | 6.4 - 8.0 | red | yellow |
| Rosolic acid | 6.8 - 8.0 | yellow | red |
| Cresol red | 7.2 - 8.8 | yellow | red |
| α - Naphtholphthalein | 7.3 - 8.7 | rose | green |
| Tropeolin | 7.6 - 8.9 | yellow | rose - red |
| Thymol blue | 8.0 - 9.6 | yellow | blue |
| Phenolphthalein | 8.0 - 10.0 | colorless | red |
| α - Naphtholbenzein | 9.0 - 11.0 | yellow | blue |
| Thymolphthalein | 9.4 - 10.6 | colorless | blue |
| Nile blue | 10.1 - 11.1 | blue | red |
| Alizarin yellow | 10.0 - 12.0 | yellow | lilac |
| Salicyl yellow | 10.0 - 12.0 | yellow | orange - brown |
| Diazo violet | 10.1 - 12.0 | yellow | violet |
| Tropeolin | 11.0 - 13.0 | yellow | orange - brown |
| Nitramine | 11.0 - 13.0 | colorless | orange - brown |
| Poirrier's blue | 11.0 - 13.0 | blue | violet - pink |
| Trinitrobenzoic acid | 12.0 - 13.4 | colorless | orange - red |