The third graders have been practicing using the scientific method as a way to give structure to their questions and explorations.
In this pH lab, students used a natural indicator – cabbage juice – to test whether 4 liquids were acidic, basic, or neutral. Students used graduated cylinders to measure 25 mL of each liquid, poured them into test tubes, and then added cabbage juice with pipettes. The cabbage juice, which starts a dark purple color, turns a brilliant pink – indicating an acid – when added to the vinegar. Students were pleased to see their hypotheses validated by this result. Some were surprised to see that Sprite was a weak acid as well, and many didn’t expect saltwater to stay purple – indicating that it is neutral. The most unexpected change was when soapy water turned the purple cabbage juice green, showing that it is a base. In one final test, students were given a cup of mystery liquid. The liquid turned the cabbage juice green, so students knew it was a base. We then mixed the vinegar from the test tube with the mystery base. When the fizzing cup nearly overflowed, students guessed correctly that the mystery liquid was baking soda in water. They quickly noticed that the combined liquids turned purple, indicating that the combination of acid and base brought the liquid back to neutral.