Cherries as a Natural Indicator

Kyle Clough, Justin Gorden, Missy Iio, Sarah Liang, Harry Wise

The purpose of this lab is to find a natural substance that acts as an acid/base indicator using sprite, water, vinegar, and bleach. An acid is a substance which dissociates into H+ ions among other ions. A base dissociates into OH- ions among other ions. An indicator reacts with these H+ or OH- ions and changes color because either the acid or base form of the indicator becomes dominant. The acid form becomes dominant when there is a high H+ concentration and the base form becomes dominant when there is a high OH- concentration.

Experimental Setup

In order to determine the pH of the four aforementioned substances, we prepared a set of pH standards. We added our natural indicator to seven substances to identify the color which the indicator turned at varying known pH levels. With this known, we could then determine the pH of the experimental substances based on the color which the indicator turned.

Household Substances After Testing

Below from left to right:

The sprite had a pH of approximately 3.

The bleach had a pH of approximately 12.

The vinegar had a pH of approximately 2.

The water had a pH of approximately 7.5.

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Conclusions

Acids resulted in red and variants of red in the indicator. Bases resulted in a range of green, brown, yellow-brown, and red-brown. Cherries are better at indicating bases, as the variation of color between pH levels is more pronounced. When in the presence of an acid, the indicator only changed color within the range of pink to red. Whereas when in the presence of a base, the indicator ranged from red to brown to green. The issue with judging the pH came when trying to discern the pH level of the acidic substances we used. It was difficult to assign them a definite pH level as the colors in the acidic range do not vary much. If we were to do this experiment again, we would choose more alkaline substances than acidic substances because it is easier to determine the pH of a base with cherries as a natural indicator.