An ester is a chemical compound formed when an acid reacts with alcohol. The general formula for an ester is RCOOR’, where R is the group of atoms that make up the acid and R’ is the group of atoms that make up the alcohol. An ester is named by combining the name of an alcohol-derived element with the name of the acid-derived element. It ends with “-oate” or “-ate.” For example, the ester formed from ethanol and acetic acid would be named “ethanoate” or “acetoate.”