03.31.2016
Written By: Nancy Trejo
Last week, the students explored reaction thermochemistry by determining whether a reaction was endothermic (absorbed heat) or exothermic (released heat). This week they studied reaction kinetics which deals with how fast a reaction takes place. They experimented with the reaction between baking soda and vinegar. Their first task was to determine which one is an acid and which is a base using cabbage juice, which changes color based on pH.
Baking soda turned blue and was therefore a base, while vinegar turned pink indicating it was the acid. When the two are mixed the solution color changes from pink to violet which signals the end of the reaction. This is also when the reaction is close to neutral. The students timed this color change and recorded the reaction time. What happens if the solution is ice cold? How fast is a hotter solution? They explored these questions by heating up or cooling down the vinegar, adding baking soda, and measuring the reaction time. The reaction was faster as the temperature increased. We also demonstrated this effect at the front of the classroom with glowsticks. The glowsticks glowed brighter in hot water compared to ice water.
I think the students really enjoyed this experiment. Next time, we can encourage them to explore other acid-base reactions. The range of pH pictured below were made using mixtures of lemon juice, apple juice, neutral solution, egg whites, baking soda, and bleach (left to right). The students may find it interesting to mix, for example, lemon juice and baking soda or apple juice and egg whites. Would these reactions have different reaction kinetics?