How do I calculate molarity, and the percent error for the following experiment?

While I am not quite sure what molarity your experiment is asking for, I am sure that buffers are quite possibly the most important thing you will use in any chemistry or biochemistry lab. Many molecules that chemists use will require certain pH ranges for any reactions with them to be carried out. Imagine if we just used water for all those reactions - pH values would be all over the place, as excess ions altered the acidity of our reactions (and their effectiveness). Buffers provide scientists with a way to maintain a steady pH while their reactions occur. From personal experience, using a buffer can mean the difference between effectively carrying out an enzymatic reaction in solution and killing ever single protein you were given by using only water.