All alkalis are chemical bases, but not all chemical bases are considered alkalis. A base is only considered an alkali if it can fully dissolve in water. Many metal oxides act as bases but refuse to dissolve in water.
They simply sink to the bottom of a beaker as a solid powder. True alkalis mix perfectly into the water to form a uniform solution. These dissolved alkalis share several distinct physical and chemical properties in the laboratory.
They taste very bitter, though you should never taste chemicals in a lab. They safely turn red litmus test paper to a bright blue color. They also feel extremely slippery or soapy to the bare touch.
This slippery feeling occurs because the alkali reacts with the natural oils on human skin. It begins turning those skin oils into literal soap through a process called saponification. Strong alkalis are highly corrosive and can cause severe chemical burns.
Alkalis react rapidly with acids in a process called a neutralization reaction. This chemical reaction destroys both the acid and the alkali. The neutralization process produces harmless liquid water and a newly formed chemical salt.
Chemistry students routinely encounter mild alkalis in everyday household items like baking soda. They can also find much stronger alkalis inside dangerous household oven cleaning sprays.