Because the anthocyanin contained in purple kale is very rich, can be used to make their own acid-base indicator, and white vinegar, water, baking soda are acidic, neutral and alkaline substances, according to the acid-base indicator red, alkaline blue or light green principle, the purple leaf kale juice were added to the white vinegar, water, baking soda, these kinds of solutions will show a different color.

Expanded:

Acid-base indicators are a class of organic weak acids or organic weak bases of more complex structure, which are able to partially ionize into ions and hydrogen ions (or hydroxide ions) of the indicator in solution, and whose molecules and ions have different colors due to structural variations, and thus show different colors in different pH solutions.

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