Three things that we learned in this unit are acids and bases. An acid is a compound that releases hydrogen irons in water. Bases are a compound that releases hydroxide irons when dissolved in water. The other thing we learned about is the pH scale. The ph scale is a set of numbers between 0 and 14 used to measure the strength of acids bases. What my favorite project was Chemistry in a Bag. There is nothing I i liked least in this unit. Here is my question what is a molecule?