How to Determine Acidity

The concentration of hydrogen ions, H+, determines the solution's acidity. This concentration is expressed as pH, that is, -log10([H+]). For example, if the concentration of H+ ions in the solution is 0.001 M, then pH = -log10(0.001) = 3. Electronic instruments called pH meters measure pH quickly and accurately. The other method of acidity determination requires the use of pH paper indicators that change color based upon a pH value.

Things You'll Need

• pH meter Distilled water Hydrion pH paper

Instructions

With pH meter

1. Rinse the pH meter glass electrode with the distilled water.

2. Place the glass electrode in the solution you are measuring and wait 20 to 30 seconds.

3. 

   Write down the pH value displayed by the instrument.

With pH Paper

1. Detach a strip of the Hydrion pH paper (see Resources), or cut a piece about 2 inches long.

2. Holding one end of the pH paper strip, put the other end into a solution for 1 to 2 seconds and then take it out. The part of the paper that was in the solution should change color.

3. 

   Compare the color of the paper with the scale printed on the pH paper pack and assign pH accordingly.

References

• "Chemistry"; K.W. Whitten, R.E. Davis, L. Peck and G.G. Stanley; 2009

Resources

• Micro Essential Laboratory: Hydrion pH paper