Acidity and alkalinity of the solution

The water we drink in our daily lives has certain acidity and alkalinity, but we cannot see it clearly through our taste buds and our eyes. We can use professional methods to detect what substances are in the water solution. The acidity and alkalinity of the solution affects our daily body, so choosing the appropriate acidity and alkalinity solution is a very important point.

The simplest way to identify the acidity and alkalinity of a solution is to use pH test paper, but the accuracy of these test papers is not very precise, so in daily life you can roughly judge the acidity and alkalinity and choose a solution that suits you. There are many other methods to test the acidity and alkalinity of solutions, which we need to learn more about.

Acidity and alkalinity have different definitions at different stages in history, some of which have long been eliminated, while others have been used to this day. Generally speaking, acidity and alkalinity refer to the property of causing the acid-base indicator to change color, but not all acids and bases can cause the acid-base indicator to change color, which requires an accurate definition.

Arrhenius acid

Arrhenius believed that acids are compounds in which all cations ionized in water are hydrogen ions, and bases are compounds in which all anions ionized in water are hydroxide ions. Acidity/alkalinity corresponds to acid/alkalinity respectively. Acidity is the property that can turn purple litmus red and can neutralize with alkali to produce water and salt. Alkalinity is the property that can turn purple litmus blue and can neutralize with acid to produce water and salt. Since the concentrations of hydrogen ions and hydroxide ions in water are measurable, the strength of acids and bases can be described quantitatively, which gives rise to the concepts of strong acids and weak acids. It is important to note that although some substances are not acids/bases according to this definition, they can still possess acidic/alkaline properties, for example, sodium bicarbonate is not an alkaline, but its aqueous solution is alkaline.

Bronsted acid base

Bronsted and Laurent believed that acids are proton donors, bases are proton acceptors, and that acids and bases have a conjugated relationship. Therefore, acidity is the property of a substance that can donate protons to a base, and alkalinity is the property of a substance that can accept protons provided by an acid. Similarly, in this theory we can quantitatively describe the strength of acids and bases. In addition, although some substances still do not meet the acid-base definition of this theory, they can still have acidity/alkalinity. For example, pure sulfur trioxide cannot donate protons but has strong acidity.

Lewis acid base

Lewis believed that acids are electron acceptors and bases are electron donors. This theory can explain the origin of the acidity and alkalinity of most substances and is extremely widely applicable. However, it cannot give a quantitative relationship between the strength of the acidity and alkalinity, and sometimes the acidity and alkalinity cannot even be compared. For example, both boron trifluoride and boron trichloride are strong Lewis acids, but in some acid-base reactions, boron trifluoride is more acidic than boron trichloride, while in other cases, boron trichloride is more acidic than boron trifluoride. The specific comparison of the strength of acids and bases is a major difficulty in the Lewis acid-base theory. The HSAB proposed later made up for this shortcoming to a certain extent.

By reading this article, we can have a good understanding of the acidity and alkalinity of solutions. These acidity and alkalinity can be as detailed as the water we drink daily. The combination of these solutions is related to our daily life and plays a vital role in the health of the body. Therefore, we must learn more about the solutions in our daily life.