Reaction Chemistry: Theoretical Predictions H 3 C 6 H 5 O 7 (aq) + 3NaHCO 3 → 3CO 2 (g) + 3H 2 O (l) + NaC 6 H 5 O 7 (aq) 1 Tablet of Alka-Seltzer contains 1 gram of citric acid and 1.916 grams of sodium bicarbonate (baking soda) (1g citric acid)/(136 g/mol) = 0.00735 mol citric acid per tablet (1.916g baking soda)/(48g/mol) = 0.0400 mol baking soda per tablet Using 6 tablets: – (6*0.00735 mol citric acid)/(3 mol CO2/1 mol citric acid) = 0.1323 mol CO2 – P=nRT/V P=(.1323 mol CO2)(.08205 L*atm/(mol*K))(273 K)/0.600 L = 4.94 atm Using 5.5 tablets, the pressure in the bottle is 4.53 atm Using 6.5 tablets, the pressure in the bottle is 5.35 atm Using 7 tablets, the pressure in the bottle is 5.76 atm
Testing Results: Data + Plots # of Alka-Seltzer Tablets amount of water used (mL) Distance (ft) 810030 81004 7 28 6.510018 6.510022 610015 Practice Trials Data Table: Testing Trials Data Table: # of Alka-Seltzer Tabletsamount of water used (mL)Distance 6100180 in - out (9.8 ft) 6100out 6100out
Conclusion: Performance and Re-Design Ideas Performance: In trial runs, our car perform fairly consistently with good results. On the day of the finals, our car did not perform as it did previously. We believe this is because the plastic had bent overnight beneath the pressure of the water bottle and rubber bands. We re-designed it towards the end of the finals but the new lightweight design could not withstand the acceleration that our previous design could. Because we were not able to practice consistently on this new design, it spun out of control on all three runs during the competition. Re-Design Ideas: A lightweight design with the propel bottle positioned lower to the ground. To compensate for the new design, less tablets and water would need to be used. It would also be beneficial to make sure the wheels could move freely and travel in a straight line by allowing them more room to spin.