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When lemon juice concentrate and vinegar are separately mixed with baking soda the reaction between lemon juice and baking soda is larger and lasts longer? Why is this?
Question Date: 2019-02-22
Answer 1:

This is a great question! As you probably know, in both cases, the reaction you see is the result of mixing an acid (vinegar or lemon juice) and a base (baking soda, AKA sodium bicarbonate). In each case, a neutralization reaction occurs, where hydrogen ions from the acid, particular acid combine with the oxygen atoms from the bicarbonate in the baking soda to form water. A biproduct of the reaction is carbon dioxide, which is the gassy bubbles we can observe as the reaction is taking place.

So what is the difference between vinegar and lemon juice? Vinegar has acetic acid, whereas lemon juice has citric acid. Your question about the duration of the reaction has to do with a quantity called pKa, which tells us about the extent to which an acid is willing to give up its protons (hydrogen). It turns out that a lower pKa indicates a stronger acid (i.e., the acid is more "willing" to give up its protons). Acetic acid (vinegar) has a pKa of about 4.74. Citric acid, on the other hand, is actually what is called a triprotic acid, which means it has 3 hydrogen ions it is "willing to give up" to the base. The pKa associated with the first proton is about 2.9, the second is about 4.9, and the third is about 5.2. This means that the first proton can be given up quite readily, and after that, the second and third protons may also be given up, depending on the conditions of the reaction (and how basic your base is!). Thus, the lemon juice can continue to react with baking soda even after the first proton is released, unlike acetic acid, which only has one proton to give up. I hope this helps!

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