CHEM 2124
General Chemistry II
Extra Credit Challenge Problem #3
Name
SOLUTION
YOU MUST SHOW ALL WORK ON CALCULATIONS TO RECEIVE ANY POINTS!!!
Titration Calculations and Buffers – GOOD LUCK!!!
1. a. A 9.0 gram tablet of generic antacid containing an unknown amount of sodium
bicarbonate is titrated to the thymol blue endpoint with 21.43 mL of 0.500M HCl. How
many grams of sodium bicarbonate are found in each 9.0 gram tablet? (+2)
1) ? moles of acid  21.43 mL HCl x 1L/1000mL x 0.500 moles HCl/L = 0.0107 moles HCl
2) 1:1 mole ratio in balanced equation so 0.0107 moles Sodium Bicarbonate (the
base)
Molar mass of Sodium Bicarbonate (NaHCO3) is 84 grams/mole
3) ? grams of base  0.0107 moles x 84 grams/mole = 0.9 grams NaHCO3
b. What is the % by weight of sodium bicarbonate in each antacid tablet? (+1)
If the tablet weighs 9.0 grams and 0.9 gram is Sodium Bicarbonate, then the % by
weight is 0.9 / 9.0 x100 = 10%