Final answer:
Sodium bicarbonate is added to local anesthetic preparations as a buffer to maintain pH balance, making the anesthetic more effective. This helps numb the area where the anesthetic is applied.
Step-by-step explanation:
Sodium bicarbonate, also known as baking soda, is added to local anesthetic preparations because it acts as a buffer to maintain a pH balance. Local anesthetics like lidocaine and novocaine are acidic, and the addition of sodium bicarbonate helps neutralize the acidity, making the anesthetic more effective. This is important because anesthetics need to be in their uncharged form to cross cell membranes and block sodium channels, which helps numb the area where the anesthetic is applied.