Barbara Hoculik, age 11, of St.Catharines, Ontario, Canada, for her question:

How do acid chemicals work?

There are a zillion miraculous operations in the world of chemistry. All of them take place in the miniature realm of atoms and molecules. The countless complex details seem overwhelming. But when you know how acids work, the total topic of chemistry looks a lot less confusing.

There are more than half a million different chemicals in the world and each must obey its own rules of behavior. Though each one is different, some resemble each other by sharing certain behavior patterns. Citric acid is a mild organic chemical found in lemons. Sulphuric acid is an inorganic chemical with violent corrosive qualities. It is manufactured for use in industry. From the human viewpoint, these two substances 'are dramatically different. From the chemical viewpoint, both of them are acids that must obey the strict rules of acid behavior.

The molecules of all acid compounds contain hydrogen atoms that separate or dissociate when dissolved in mater. This dissociation produces free hydrogen ions, each hearing a positive electrical charge. The departing hydrogen ions leave smaller molecules called acid radicals. If a piece of zinc is placed in a solution of sulphuric acid dissolved in water, the zinc atoms combine with the acid radicals to form molecules of zinc sulphate, while the freed hydrogen escapes as a gas. Hydrogen ions in acids may be replaced with several different metals to form different compounds.

These and other acid activities are powered by electrical energy. This energy is present in all molecules, atoms and atomic particles. And it works because it comes in two opposite forms. In the atomic world there are positive and negative electrical charges. The laws of chemistry say that like charges repel each other and that particles bearing opposite charges are attracted to each other. Charged particles are ions. When acids dissociate in water, their molecules free positive hydrogen ions. This leaves depleted molecules called acid radicals. Some of the positive ions attach themselves to the negative poles of water molecules. These remade molecules become positive hydronium ions with impulses to seek for negative ions.

Quantities of negative ions may be supplied by a class of chemicals called bases. In water, a base dissociates and frees particles of hydrogen and oxygen in the form of negative hydroxide ions, along with positively charged metallic ions. When acid is added to the base solution, some of the negative hydroxide ions from the base combine with the positive hydrogen ions from the acid to form water mole¬cules. The other dissociated ions in the solution, the acid radicals and the positive metal ions, also pair of, forming electrically neutral molecules which belong in the class of salt chemicals.

The basic ground rules of all acids are the same. In water, they release positive hydrogen ions eager to team with negative ions. When other substances, such as a base or a metal, are added to the solution, the original molecules are reshuffled into different chemical compounds. Each of the many acids obeys the ground rules in its own way. Strong sulphuric acid dissociates almost all its ions fast and furiously. Weak boric acid gently loses dust a few of its ions. And each acid reacts with each of the many bases to form a different type of chemical salt.