This activity has been provided by STEAMfest sponsor MEL Science!”
Sprinkle baking soda into the saucepan and pour vinegar over it. Stir thoroughly. Put the resulting solution on the hot plate and evaporate until it turns dry, and try to break up the lumps of the resulting powder. Then put the powder in the glass container, add water and heat in a water bath until it dissolves completely. Move the resulting solution to the beaker and allow to cool. Touch with your finger. Observe the formation of crystals and the release of heat.
In the reaction of acetic acid and sodium bicarbonate, sodium acetate forms. It has a very interesting property–it dissolves in its own crystallized water when heated. A saturated solution forms, which when it cools is very unstable and crystallizes from any impact, for example the touch of a finger.
However, in our experiment we dried the sodium acetate out completely, so it was easier to calculate the amount of water needed. This is so crystal hydrate forms–a solid salt with water molecules in a crystal lattice. For every 100 g of sodium acetate, around 66 g of water is required.
NaHCO₃ + CH₃COOH = CH₃COONa + CO₂ + H₂O
CH₃COONa•3H₂O(solid) = CH₃COONa(solution)
You can purchase acetic acid from any lab chemical supplier. Alternately you can create your own “9% acetic acid solution” by starting with 70% industrial vinegar (vinegar essence) and diluting to 9%. Here’s an article that explains the procedure:
- Did the experiment work as shown in the video?
- What did it feel like when you stuck your finger in the glass?
- How did you make the acetic acid solution?
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