Put simply, the pH value indicates how acidic or alkaline a solution is. If you want to know more, we can also tell you that the pH value is actually a measure of the amount of hydrogen ions present in water. Still not enough for you? Then pay attention: The pH value is the negative decadal logarithm of the hydrogen ion concentration. Okay, let's take it easy again: The pH value is specified in a range of 0-14. A neutral solution with a pH of 7 contains the same amount of hydrogen and hydroxide ions. In an acidic solution (pH less than 7), there are more hydrogen ions; in an alkaline solution (pH greater than 7), hydroxide ions predominate. So that you do not have to give the hydroxide ion concentration with a power such as 109. mol/l, you draw the logarithm. However, we will now spare you the further calculation steps and would rather give you a few more example values: Pure water has a pH of 7, and our skin also prefers pH-neutral soap. Cola is very acidic and has a pH of 2-3, whereas soap suds are 8. By the way, measuring the pH of ultrapure water is very problematic and inaccurate due to the high resistance; special pH electrodes are needed to obtain a reliable value.