The substances may be acidic or alkaline. The level of acidity or alkalinity is measured by a scale known as pH, which means power-hydrogen. On a scale of pH values ranging from 1 to 14, accounting for a value more acidic substances, between 7 and 8 to 14 at neutral and more alkaline. To determine the pH of a substance there are indicators that change color when pH changes from one value to another, change is called turnaround.
Scientists of old classified substances in view of their flavor and thus, the compounds called acids taste sour, like vinegar and lemon, and called them bitter alkalis or bases, such as sodium oxide.
The hydrochloric acid has a pH, therefore, is a highly acidic substance. Vinegar is a substance less acidic, pH 4. Drinking water corresponds to an almost neutral pH value 8. hydrogen potassium, pH 14, and ammonia, pH 12, are alkaline.