Acids share several common characteristics and properties, including sour taste and corrosion to all metals. These characteristics distinguish acids from bases, which culminate the second broad class of chemical substances encountered in daily life. Acids vary widely in purpose and structure; some, such as lemons and citrus fruits, are edible and important sources of nutrition, while others exist as toxic chemicals.
Acid substances are commonly found in residential and industrial kitchens. According to UIUC, prime examples are lemons and vinegar. These substances have tart and tangy tastes, and have low pH levels. PH levels determine the acidity of certain substances; those with a pH under 7 are considered acidic, while substances with pH levels exceeding 8 are basic. Acids, like bases, take the shape of liquid, solid and gas. They vary in color and shape; some, like lemons, are yellow, while vinegars are dark brown, cherry or dark purple. All acids are corrosive to metals, which means that upon contact with metals and metallic byproducts, acids eat away at the metallic substances; this causes the visual effect of rust, and results in the production of hydrogen gas. Some acids are water soluble, while others resist disintegration when exposed to moisture. When combined with bases, acids have a neutralizing effect, and help to lower the pH level of the base.