This was the question my son asked me yesterday when picked him up from daycare to which I replied, “I don’t know! We should do some experiments.” It’s a good question and questions are what science is all about. I suggested that we DO NOT start with the original question but do some preliminary tests.
We first added a tablespoon (15 mL) of baking soda (sodium bicarbonate, NaHCO3) to a cup. Next, we added a quarter cup (~60 mL) of vinegar (dilute acetic acid, CH3COOH) to a second cup and measured its temperature with a digital meat thermometer (Thermoworks). Finally, we mixed the two compounds together while continually monitoring the temperature. Of course we repeated this experiment to make sure our results were repeatable.
They were as follows:
Initial Temp (∘F)
Final Temp (∘F)
These results were surprising to me as the reaction caused a lowering of the temperature. We found out that putting baking soda and vinegar on your face would not cause your face to burn up although I still WOULD ADVISE AGAINST this as excess vinegar could get into your eyes and inflict pain while causing damage. As a safer backup demonstration I put some baking soda into the palm of my hand and added vinegar (over the sink). It did cool off as fizzed. Of course Julian needed to feel this for himself...
The other thing we discovered was that the reaction absorbs heat from the surroundings which means that it is endothermic. We could have looked all this up but it was more fun doing the actual experiment...
Also, for those who care:
The fizzing is the carbon dioxide gas that is produced during the reaction.
NaHCO3 + CH3COOH → NaCH3COO + H2O + CO2
Note: it produces carbonic acid (H2CO3) first which quickly breaks down into water (H2O) and carbon dioxide (CO2)