Introduction
First of all, it should be stated that the classification of chemical reactions according to the pH scale defines the acidity of the included and resulting components. Originally, the pH scale was invented for measuring the acidity of the solutions, and the scale incorporates the acidity criteria elaborated by Sorensen.
Chemical Reactions
Most chemical reactions, which may be classified according to the pH scale cannot deal without H+ ions. Depending on the concentration of these ions, the hydrogen peroxide can behave as an oxidizing or reducing agent (Davis, 2002). According to Kurtzweil (1998), the pepsin is one of the enzymes engaged in the digestion process better works in the acidic conditions, and, it is absolutely inactive in neutral environment. The flowers change their color, depending on the acidity level of the soil they grow in, let alone milk that coagulates in contact with lemon juice.
As Wilbraham (1995) emphasizes
The concentration of H+ is usually confined to 1-10-14M range. Thus pH scale contains values falling between 0 and 14. In some rare cases, it is possible to see pH lower than 0 or higher than 14, when the concentration of H+ take some extreme values.
The fact is that the chemical properties of various substances and their reactions are crucial for the human body. Thus, the stomach contains hydrochloric acid and peptidase, which are engaged in the digestion process, by breaking down foods. As too much acid in stomach may cause ulcer, there is a strong necessity in a neutralizing component. An antacid is basic for neutralizing stomach acid to bring the stomach back to a pH level of 2. Thus, the chemical reaction will be the following:
2 HCl(aq) + CaCO3(s)=CaCl2(aq) + H2O(l) + CO2(g).
The opposite point of the pH scale is the alkalinity. Originally, it can be measured as Phenolphthalein Alkalinity and Total Alkalinity. This Alkalinity state may be determined by neutralizing the solution to pH 8.3 by the dilute sulfuric acid solution and a phenolphthalein indicator (Wilbraham, 1995). This process of neutralizing converts hydroxide ions to water components, and carbonate ions to bicarbonate ions:
2OH – +H2SO4 → 2H2O+SO4
2CO3 – +H2SO4 → 2HCO3 – +SO4
According to Davis (2002), bicarbonate ions can be transformed to carbonic acid with additional sulfuric acid. To convert the carbonate ions, sulfuric acid is added until the sample’s pH is 4.5:
2HCO3 – +H2SO4 → 2H2CO3 +SO4
This process is often regarded as Total Alkalinity.
The chemical reactions, which incorporate both acidic and alkaline components are often causing the neutralization of the reaction components. Thus, the pH scale will show the middle acidity and alkalinity. Originally, these features are rather significant for the matters of classifying the corrosive features and properties of water and other liquids. Still, the corrosive characteristics are generally defined by hydroxide, carbonate and bicarbonate ions. All the other sources of alkalinity may be originated from hydrolyzed anions, such as phosphate, silicate, borate, fluoride and salts of some organic acids.
References
Kurtzweil, Paula. “Alpha Hydroxy Acids for Skin Care.” FDA Consumer 1998: 30.
Davis, Raymond E., John E. Williams. Modern Chemistry. Holt, Rinehart, and Winston: 2002.
Wilbraham, Antony C., Dennis D. Staley, Michael S. Matta. Chemistry. Addison-Wesley: 1995.