Science Buddies: "Ask an Expert"

I want to do the Bath bomb experiment, but I want to use citric acid substitutes instead of citric acid. I want to use lemon juice, lime juice, cream of tartar, and distilled white vinegar, but the citric acid is stronger than these substitutions. So how much of each should I use to make the bath bombs? Also, since some are liquids, it will change the recipe and I don't know how to even out the recipe.

Yes, I am using that experiment. I know that the citric acid is stronger than the citric acid substitutes, so I will probably need to use more of the CA substitutes than the recipe calls for. Since some of those substitutes are liquids, it will make the recipe uneven, and there will probably be too much liquid for the recipe. So, how do I even out the recipe when I have a larger amount of liquid that I need to use?

Hi cdaly,

I’m assuming that you are working on the project described here:

https://www.sciencebuddies.org/science- ... p105.shtml

Substitutions for citric acid are common in cooking. Usually two to four times more of the substitute is used and I suspect that the substitute amounts differ depending on the recipe as well as the substitute.

The normal bath bomb recipe in the project procedure calls for 2 tbsp of powdered citric acid. One suggestion is to try using twice as much of your substitutes in your new recipes. You may want to experiment with the amounts you need to get the same “fizz” as with the normal recipe. Or you could use the same 2 tbsp for the substitutes and see what happens with the different bath bomb recipes.

I hope this helps. Please ask again if you have more questions.

A. Norman

I too am working on this project. What is confusing me is that if you modify the ingredients, you have to change the amount to get the recipe to work. This is now changing two variables, not just one. I thought in a Science project, you could only change one variable. Could you please explain this...I am supposed to do my experiment this weekend

Hi kbrownhhcolor,

I can definitely see how this is confusing. Whether you are changing one variable or two really depends on what you define as the independent variable. The most important thing will be to carefully describe what you do. I think you have a couple of options:

First, if you don't change the recipe, but only replace the citric acid powder with something else, then you are definitely only changing one variable. The acidity source would be the independent variable in this case. The results that you get might not very interesting, but you would have followed the scientific method to a T, changing only one variable. I don't think any science teacher would give you flack for taking this approach

Second, instead of thinking about the source of acidity (citric acid, vinegar, etc.) as the independent variable, you can think of the *recipe* as the independent variable. In this case, the differences in the recipe would be the independent variable. Personally, I would take this second route because I think it's more likely to give you interesting results. If you take this approach, then just make sure to specify that the recipe for the bath bomb, not the acidity source, is the independent variable. If you do so, then I also think that you will satisfy the science teacher.

Post back if this is still confusing to you or if you have other questions; I usually respond within 24 hours (except on Sundays). I hope your experiments go well this weekend!