What is the pH? Definition:
Of the PH value is defined as the negative decadic logarithm of the hydronium ion concentration. What that means exactly, you will learn in the course of this article. Conceptually, the letter abbreviation "pH" derives from the Latin 'potentia Hydrogenii' (potentia = force, Hydrogenium = hydrogen).
The pH indicates on a scale of 0-14 how much an aqueous solution angry or alkaline / basic is. Values from 0 to approx. 6.5 are considered acidic. Pure water has a pH of 7 and is considered neutral. Values between 7.5 - 14, on the other hand, are alkaline / basic. Values below zero, or over 14 are possible, but hardly affect the practical scope.
Using a pH indicator, the pH of a liquid can be determined easily and quickly. Add the pH indicator to a small amount of the desired liquid. This discolors the liquid, depending on the pH in the solution. However, the above color scale can not be used by default for determination, since the colors are always dependent on the respective indicator liquid. There are different indicators with different color spectrums. A popular indicator liquid for approximate determination is e.g. Red cabbage juice, which is often used in chemistry lessons.
pH value explained in more detail:
Again, back to the initial definition: The pH is defined as the negative decadic logarithm of the hydronium ion concentration (H3O+). Accordingly, the pH is calculated on the basis of the amount of hydronium ions present (instead of H3O+ usually only with H+ abbreviated) in the liquid. Because this amount is so small and it would be less than practical to write that number out every time (for example, a neutral solution of 10)-7 = 0.0000001) or as a power, one draws the negative decadic logarithm for the sake of simplicity. A decadic logarithm is the logarithm of base 10 (log of ten). The whole thing looks like this:
H+Ion concentration of 10-1mol / l = pH 1 (acidic)
H+Ion concentration of 10-7mol / l = pH 7 (neutral)
H+Ion concentration of 10-14mol / l = pH 14 (basic)
By drawing the negative logarithm, the signs can be reversed so that we do not find a pH of -7 but +7. In principle, this has no meaning in terms of content and serves only for simplification. Because theoretically, the pH values could also be given negative. The meaning that pH -7 would be a neutral liquid would remain the same.
But attention: the pH is not a unit of measurement, but a normal number, which is the absolute amount of dissolved H+Indicates ions in the liquid.
pH value table:
|1,5||Stomach acid, sulfuric acid|
|4,5||Yogurt, sour milk|
|5||Mineral water, coffee|
|5,5||human skin, rainwater|
|6,5||fresh milk, saliva|
The importance of pH for humans:
The level of pH plays an important role for the human organism in many ways. Thus, the slightly acidic ph value (5.5) of the skin protects against pathogens. The acid mantle provides an unfavorable environment and prevents bacteria from growing. Excessive washing with soap (pH 9.5) neutralises the acid mantle and makes the skin more susceptible to infection. Only a few hours after washing, the skin can restore the original pH.
Even more acidic is the human stomach acid. With a pH of 1, gastric acid not only helps decompose the food but also reliably kills harmful microorganisms. The slightly basic (pH 8) secretion from the pancreas subsequently neutralizes the stomach acid so that it does not corrode the digestive tract.