pH of the medium
in advertising often slips term pH value of the medium.Consumers are assured that it is kept at a normal level, and the company's products are safe for people.
in ordinary water at room temperature is always contained a small amount of positively charged hydrogen cations and negative hydroxide anions.They result from the reversible dissociation.In one liter of water with no impurities contained 10 * 7 moles of hydrogen cations and anions as well.For convenience of notation introduced the concept of pH, which pure water is 7. This substance is neutral in nature.There are other neutral medium.
acids and alkalis have pH value takes other values.In the case of the acids in the water dissociation may be reversible or irreversible.In any case, the content of hydrogen cations in an environment decreases.Irreversible di
ssociation characteristic of strong acids such as hydrochloric acid.Its solution contains 10 * 2 moles of hydrogen cations, pH of the solution is equal to 2. As can be seen, it is the exponent determines the value of the index of the medium.This logarithm of the number of cations, taken with the opposite sign.For acid it is always less than 7. The stronger the acid, the lower the pH.
with alkalis, the situation is a little different.At their dissociation in water appears excessive amount of negatively charged hydroxide anions.They capture a part of the cations of hydrogen and thus reduce their number.It becomes less than 10 * 7 mol.In this case, the index is equivalent to the exponent.Strong alkalis irreversibly dissociate and their pH ranges from 7 to 9. The weak alkali dissociation which has a reversible process, have a pH of 9 or higher.
With the help of special substances can define any type of fluid.These substances are called indicators.They are able to change color depending on the environment where they are placed.These include phenolphthalein and litmus.In a neutral environment, all lights do not change color.Initially, litmus purple placed in the acid solution assumes a bright red color and becomes blue in alkali.
colorless phenolphthalein as an indicator used is not as widespread as it responds to the same highly alkaline and neutral environment.But it clearly shows the lack of hydrogen cations (acidity), coloring in red.