pH Playgound (understanding pH)

Definition of pH.

Skip This! If words like pH and logarithm intimidate you, ignore this paragraph and explore the Playground below first. 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). Many of us find that pH confuses us because we are not entirely comfortable with Logarithm. Moreover, as the acidity increases, the pH decreases. The Playground below is designed to take the mystery out of pH. Every item has been put there to play with and help you get familiar with the numbers.

Try the pH Playground

Buttons: Click the plus and minus 0.1 buttons and compare the values to the teaching scale on the right. Then click on the other buttons. Watch the Units, the pH and the [H⁺]. Thus, button number 2 decreases the pH by 1.0 and increases the [H⁺] tenfold whereas button 6 halves the [H⁺] with a pH increase of 0.3.

Teaching uses approximate values which can quite easily be remembered. Change it to "Accurate" to produce accurate results.

pH to [H⁺] converts from the red pH values. [H⁺] to pH converts from the black [H⁺] values.

nanoMol/L: Change the units and watch the pH change in steps of 3.

Enter values: Type a number into either box and press Enter or Return to see the conversion.

pH change of 3 [H⁺] Steps of 1000	pH change of 1 [H⁺] Steps of 10	pH change of 0.3 [H⁺] Steps of 2	pH change of 0.1 [H⁺] Steps of 1.25

Comments.

Teaching mode gives a good approximation of the relationship between pH and [H⁺]. The numbers on the right are colored to show how progressive steps of doubling can be used to generate an approximate table of logarithms. Each number is double the one which is separated by a step of pH 0.3. Playing with doubling and halving shows how this table can be generated (if you really want to do this - see the tables at the bottom of this page). The actual numbers in a given range may be ten-fold different - but easily recognizable.

Clinical Range. The actual clinical range is from about 80 down to 20 (pH 7.1 to pH 7.7). This range is comparable to other clinical variables. In medicine we really don't benefit from using pH. We would probably have done better if we had been brought up to use [H⁺]. Too late now!

Accuracy. It is useful to compare the discrepancy between Teaching Mode and Accurate Mode by repeatedly clicking any of the four middle buttons, first in one mode and then in the other. In accurate mode you can use either [H⁺] to pH or pH to [H⁺].

Make Yourself a pH Table.

This is the way to really conquer logarithm and pH. First step down in thousand fold jumps (See Table below). 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.

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

Starting Numbers: Next, write a list of pH values starting at 8.0 and finishing at 6.8 (See Table below). Below these numbers, write in the the values for pH 8.0 and 7.0 from the table above. These numbers are starting points.

Now make use of: x 2 = + 0.3 i.e., a log jump of 0.3 corresponds almost exactly to doubling. Now, halve 100 (50, 25, 12.5) and double 10 (20, 40, 80, 160) to obtain the numbers in the table. When you get to 160, pH 6.8 is a tenfold jump away from pH 7.8 (16 followed by 32, 64, 128). Notice that the final number you insert (128 for pH = 6.9) also demonstrates the slight error of this method. Compare it to the value for pH = 7.9 (12.5). The correct values are 126 and 12.6 - not errors which would be critical in medicine.

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

Acid-Base Tutorial
Alan W. Grogono