Acid Test for Science Fair

Science fair project: use baking soda solution and purple cabbage indicator to compare candy acidity. Purple cabbage indicator (made by boiling, or soaking, purple cabbage in water) changes color based on pH. If you add a base, it turns blue, and if you add acid, it turns pink. Here's the original color.

First, we dissolved various candies in indicator. The brightest pink are the most acidic.

Then we added baking soda water to each sample to bring it to neutral, and compared how much soda we used for each sample to arrive at an acidity comparison.

One fun little thing: to dissolve the maximum amount of soda in water, we warmed the water up. As it cooled, the soda started to crystallize again. Apparently, our initial solution was a little supersaturated.


  1. First question, can I use this for my science fair project? And secondly, will the sour candies work? Last question, how do I graph my results?

  2. You can use this for the science fair project, as long as you list as your source. Sour candies do work, although since some are more sour than others, there will clearly be results from different candies. Make sure the candy is completely dissolved before testing. To graph your results, you will have to graph the variable that changes. For the above experiment, you could graph how much baking soda water you added to each solution to make it neutral.


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