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This drawing represents a comet bringing atmospheric molecules and possibly primitive life forms to the Earth's surface.
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Base

Like an acid, a base is a substance capable of dissolving things. Unlike an acid in which the active agent is a substance which has a positive electric charge (H+), in a base the active agent has a negative charge (OH-). Here are a couple of scientific explanations of what a base is:

A base is any substance that upon dissolving in water increases the hydroxide ion content (OH-). An base can also be thought of as a substance which accepts a proton from another species in a reaction. (Here, "accept" is a passive term for what really happens. A base attacks and "rips" a proton from a substance which has any capability of giving it away. Thus a base accepts a proton the way a thief "accepts" your purse). Bases are classified as either strong or weak depending upon their relative ability to do this.

There are many bases. Here are a few: Ammonia (used as a cleaner), Calcium hydroxide (used in mortar for construction), Magnesium hydroxide (otherwise known as milk of magnesia; used as a laxative or antacid), Sodium hydroxide (used as an oven cleaner).

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