There are many naturally occurring acids in coffee. For the Q certification, 4 specific acids are explored; citric, malic, acetic & phosphoric. One exercise is called 'matching pairs' which tests the user's ability to differentiate, recognize & recall these specific acids in coffee. The acids here are sold separately as 1 Molar each (4 oz.) or together as 4 bottles sold as a kit with 1 of each of the acids.