Base (chemistry)
![Soaps are weak bases formed by the reaction of fatty acids with sodium hydroxide.](/Images/godic/202502/04/Decorative_Soaps0033.jpg")
![Ammonia fumes from aqueous ammonium hydroxide in test tube reacting with hydrochloric acid (in beaker) to produce ammonium chloride (white smoke).](/Images/godic/202502/04/Hydrochloric_acid_ammonia0033.jpg")
In chemistry, bases are substances that, in aqueous solution, are slippery to the touch, taste astringent, change the color of indicators (e.g., turn red litmus paper blue), react with acids to form salts, promote certain chemical reactions (base catalysis), accept protons from any proton donor, and/or contain completely or partially displaceable OH ions. Examples of bases are the hydroxides of the alkali metals and alkaline earth metals (NaOH, Ca(OH)2, etc.).