What kind of environment is referred to as acidic, what to alkaline
What kind of environment is referred to as acidic, what to alkaline
In chemistry there are alkaline, acidic and neutral environments. They have a qualitative difference, which consists in a hydrogen pH (from the Latin pundus hydrogenium - "weight of hydrogen").
The hydrogen index of the medium
In advertising, the concept often slipshydrogen index of the medium. Consumers are assured that it keeps at a normal level, and the company's products are safe for people. In ordinary water at room temperature, there is always a small amount of positively charged hydrogen cations, as well as negative hydroxide anions. They are formed as a result of reversible dissociation. In one liter of water without impurities, 10 * 7 moles of hydrogen cations and the same number of anions are contained. For convenience, the notation introduced the concept of a hydrogen index, which for pure water is 7. This substance is neutral in nature. There are other neutral media. In acids and alkalis, the hydrogen index takes on different values. In the case of acids, their dissociation in water can be reversible and irreversible. In any case, the content of hydrogen cations in such a medium decreases. Irreversible dissociation is characteristic of strong acids, for example, hydrochloric acid. In its solution contains 10 * 2 mole of hydrogen cations, the pH of such a solution is 2. As can be seen, it is the exponent that determines the value of the index of the medium. This is the logarithm of the number of cations taken with the opposite sign. For acids, it is always less than 7. The stronger the acid, the lower the pH. With alkalis, the situation is slightly different. When they dissociate in water, an excess of negatively charged hydroxide anions appears. They capture part of the hydrogen cations and thus reduce their number. It becomes less than 10 * 7 moles. And in this case the value of the indicator is equivalent to the exponent. Strong alkalis dissociate irreversibly and their pH varies from 7 to 9. Weak alkalis, the dissociation of which is a reversible process, have pH values from 9 and above.Indicators
With the help of special substances can determinethe type of any liquid medium. These substances are called indicators. They are able to change color depending on the environment where they are placed. They include phenolphthalein and litmus. In a neutral environment, all indicators do not change their color. Initially, the purple litmus placed in the acid solution acquires a bright red color and turns blue in alkali. Colorless phenolphthalein as an indicator is not so widely used, since it reacts equally to a strongly alkaline and neutral medium. But it well shows the lack of hydrogen cations (the acidity of the medium), coloring in red.
