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pH - Basic (alkaline) vs. Acidic

Introduction to pH - the acidic and basic (alkaline) definition.

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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
pHIon 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

pH vs. Acid Hydrogen and Basic Hydroxide ions

Download and print pH Ion Concentration Chart

Some common Products and their pH Values

pH values in some common products:

pH in Common Products
ProductpH
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

pH - Acid-Base Indicators
IndicatorpH - RangeColor Cange
AcidBase
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
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