Acids are very common in some of the foods that we eat. Citrus fruits such as oranges and lemons contain citric acid and ascorbic acid, which is better known as vitamin C. Carbonated sodas contain phosphoric acid. Vinegar contains acetic acid. Your own stomach utilizes hydrochloric acid to digest food. Acids are a distinct class of compounds because of the properties of their aqueous solutions as outlined below:
- Aqueous solutions of acids are electrolytes, meaning that they conduct electrical current. Some acids are strong electrolytes because they ionize completely in water, yielding a great many ions. Other acids are weak electrolytes that exist primarily in a non-ionized form when dissolved in water.
- Acids have a sour taste. Lemons, vinegar, and sour candies all contain acids.
- Acids change the color of certain acid-base indicates. Two common indicators are litmus and phenolphthalein. Blue litmus turns red in the presence of an acid, while phenolphthalein turns colorless.
- Acids react with active metals to yield hydrogen gas. Recall that an activity series is a list of metals in descending order of reactivity. Metals that are above hydrogen in the activity series will replace the hydrogen from an acid in a single-replacement reaction, as shown below:
Zn(s)+H2SO4(aq)→ZnSO4(aq)+H2(g)
- Acids react with bases to produce a salt compound and water. When equal moles of an acid and a base are combined, the acid is neutralized by the base. The products of this reaction are an ionic compound, which is labeled as a salt, and water.
It should not be hard for you to name several common acids (but you might find that listing bases is a little more difficult). Below is a partial list of some common acids, along with some chemical formulas:
| Chemist Name | Common Name | Uses |
|---|---|---|
| hydrochloric acid, HCl | muriatic acid (used in pools) and stomach acid is HCl | Used in cleaning (refining) metals, in maintenance of swimming pools, and for household cleaning. |
| sulfuric acid, H2SO4 | Used in car batteries, and in the manufacture of fertilizers. | |
| nitric acid, HNO3 | Used in the manufacture of fertilizers, explosives and in extraction of gold. | |
| acetic acid, HC2H3O2 | vinegar | Main ingredient in vinegar. |
| carbonic acid, H2CO3 | responsible for the “fizz” in carbonated drinks | As an ingredient in carbonated drinks. |
| citric acid, C6H8O7 | Used in food and dietary supplements. Also added as an acidulant in creams, gels, liquids, and lotions. | |
| acetylsalicylic acid, C6H4(OCOCH3)CO2H | aspirin | The active ingredient in aspirin. |
What exactly makes an acid an acid, and what makes a base act as a base? Take a look at the formulas given in the above table and take a guess.