Final answer:
Acids are characterized by a greater concentration of hydronium ions than water, resulting in a pH below 7, and a sour taste. Carbonic acid in soda is an example of an acid, while hydrochloric acid is a strong acid found in the stomach.
Step-by-step explanation:
The qualities that define acids include having a greater concentration of hydronium ions (H3O+) than water, which results in a pH lower than 7. Acids are characterized by their sour taste, such as that of vinegar or citrus fruits. This sour taste is a common property of acids and is a practical way to identify them. Additionally, acids like carbonic acid in soda contribute to the beverage's tangy taste, while stronger acids can be harmful to organisms and materials. For example, hydrochloric acid is a strong acid that can damage materials like glass and is also present in the stomach, where it aids digestion and kills harmful microbes.