An alkali is a type of chemical substance that often feels slippery like soap and can neutralize acids. Common alkalis include baking soda and substances used to make soap and lye (a powerful cleaner). When you wash your hands with many soaps, that slightly slippery feeling can come from alkaline ingredients.

Scientists identify alkalis by testing them with special paper called litmus paper, which turns blue when it touches an alkali. On the pH scale (a measure of how acidic or alkaline something is), alkalis score above 7. The opposite of an alkali is an acid, like lemon juice or vinegar.

In chemistry class, you might see dramatic demonstrations where alkalis neutralize acids: pour an alkali into an acid, and they react, often fizzing and creating heat. This reaction is useful in everyday life. When your stomach feels upset from too much acid, an antacid tablet uses alkalis to neutralize that acid and make you feel better.

Strong alkalis like drain cleaner can be dangerous and burn skin, so scientists handle them carefully. But weaker alkalis like baking soda are safe enough to eat and bake with when used correctly.