The reader will observe that there are as many parts of each element on the right as on the left-hand side of the = mark. Two parts of common salt yield two parts each of sodium (Na) and chlorin (Cl). The sodium appears as Na in the sodium sulfate, and the chlorin as Cl in the two parts of hydrochloric acid.
This method of expressing chemical action by these equations may be somewhat confusing at first to those who have not studied chemistry, but it is best to have all such become familiar with them that they may have the further benefit of understanding the general terms of chemistry.
Hydrochloric acid gives up its hydrogen when brought into contact with certain metals like iron, zinc, etc., and takes up these metallic elements in place of the hydrogen. Thus zinc and hydrochloric acid give zinc chlorid and hydrogen.
Zn + 2HCL = ZnCl2 + H2
Zinc + Hydrochloric acid = Zinc chlorid + Hydrogen
ACIDS, BASES, NEUTRALIZATION, SALTS
We have already discussed a number of substances called acids. It is necessary to inquire why chemists call them acids. What is there in common, for example, Relation of acids to bases between the heavy, oily liquid sulfuric acid and the colorless gas, hydrochloric acid? It is not possible to understand the nature of their common properties without examining a class of substances called alkalis or bases.
Acids and bases have the power to destroy the characteristic properties of each other. When an acid is brought into contact with a base, in proper proportions, the characteristic properties of both the acid and the base are destroyed. They are said to neutralize each other.
The most common acids are sulfuric, hydrochloric, and nitric. Among the more common bases are caustic soda, caustic potash, and lime. A convenient way to recognize whether a substance has acid or basic properties is by means of certain Common acids and bases and tests therefor color-changes. Litmus is a coloring matter which is ordinarily blue. If a solution which is colored blue with litmus be treated with a drop or two of an acid, the color is changed to red. If the red solution be treated with a few drops of a solution of a base, the blue color is restored.
Many substances change in color according to whether the solutions in which they are present are acid or alkaline. An infusion of red cabbage, for example, changes color when treated with an acid, and recovers its color when again treated with an alkali.