Definition of pH.
Caution! If words like pH and logarithm intimidate you, skip this paragraph and go straight to the Playground below. The pH is the negative logarithm of the [H+] measured in moles per liter. A pH of 7.4 is equivalent to 40 nanoMols/liter [H+] (hydrogen ion concentration).
pH confuses many of us because we are not entirely comfortable with Logarithm. Moreover, as the acidity increases, the pH decreases. The Playground below is designed to take mystery out of pH.
Try the pH Playground
The Clinical Range is between about 80 and 20 nanomol/L (pH 7.1 to pH 7.7). Approximate values make it easier to visualize the Hydrogen Ion concentrations. Watch the pH, the [H+] and the Units. Observe how cumbersome dilute [H+] concentrations are in mol/L – hence the use of pH.
Buttons: Click on the Blue Multiply or Divide Buttons. For example, x2 and /2 double or halve the [H+] concentration and x10 and /10 have a tenfold effect.
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Conquer pH Yourself
| Number | Log | pH | Concentration |
| 1,000,000 | 6 | -6 | 1 megaMol/L |
| 1,000 | 3 | -3 | 1 kiloMol/L |
| 1 | 0 | 0 | 1 Mol/L |
| 0.001 | -3 | 3 | 1milliMol/L |
| 0.000,001 | -6 | 6 | 1 micMol/L |
| 0,000,000,001 | -9 | 9 | 1 nanoMol/L |
| 0,000,000,01 | -8 | 8 | 10 nanoMol/L |
| 0,000,000,1 | -7 | 7 | 100 nanoMol/L |
Steps of 1000. First step down in thousand fold jumps (See First Table). Of course it is impossible to make such concentrated solutions as a megaMol/L, but most of us can remember the logarithm of a thousand and a million.
Starting Numbers: Next, write a list of pH values starting at 8.0 and finishing at 6.8 (Second Table). Below these numbers, write in the values for pH 8.0 and 7.0 from the first table. These numbers are starting points.
| 8.0 | 7.9 | 7.8 | 7.7 | 7.6 | 7.5 | 7.4 | 7.3 | 7.2 | 7.1 | 7.0 | 6.9 | 6.8 |
| 10 | 12.5 | 16 | 20 | 25 | 32 | 40 | 50 | 64 | 80 | 100 | 128 | 160 |
Now use +0.3 = x 2: i.e., a log jump of 0.3 corresponds almost exactly to doubling. From 100 divide by two to get the blue boxes: 50, 25, 12.5. Then from 10 multiply by 2 to get the pink boxes: 20, 40, 80, 160. From 160 (pH 6.8) a ten-fold dilution reaches 16 (pH 7.8). From 16 doubling gives the grey boxes 32, 64, 128. Notice that the final number, 128 for pH = 6.9 also demonstrates the accuracy of this method. Compare it to the value for pH = 7.9 (12.5). The correct values are 126 and 12.6 – not critical in medicine.