11.03.2016
Written By: Bryan Voight
This week, students studied how quickly reactions take place, i.e. reaction kinetics. The core experiment involved the acid/base reaction between baking soda and vinegar. Cabbage juice was used as a pH indicator to first determine that baking soda was a base and vinegar an acid, then as a way to monitor how these neutralized each other when combined. Baking soda turned the cabbage juice blue, and vinegar turned it red. When combined, the solution turned violet, signifying the completion of the reaction when the pH was close to neutral (7). Students then experimented with and recorded how the time required to get a purple color changed when cold, room temperature, and warm solutions were used. As the temperature increased, the reaction sped up. This effect was also demonstrated by showing how glowsticks glowed brighter when warm than cold. Different variables in the acid/base reaction were experimented with; ratios of vinegar and baking soda, amounts of each, as well as how reaction time changed when using hydrochloric acid instead of vinegar, and sodium hydroxide instead of baking soda. Kids seemed to enjoy experimenting with all of the different available variables, particularly in scaling up the reactions (due to the fizzing) – looks like we have a bunch of chemical engineers on our hands! Using hydrochloric acid and sodium hydroxide were cool, though we got some interesting solution colors, including a vibrant green and yellow. These were not anywhere in the expected pH color range, so there must have been other coloring agents in the cabbage juice that had color changes with pH as well!