Hielo Facil

Step 1Preparation

iWe'll be making approximately 330 mL (or 11 fl oz) of supersaturated solution.

You will need the following items:

- One 16 oz box of baking soda (sodium bicarbonate)
- One gallon jug of distilled white vinegar (acetic acid)
- Clean pot for boiling (5.5 Qt or larger)
- Another clean pot for filtering (4 Qt or larger)
- Pack of coffee filters (basket style, notfunnel shaped)
- Small wire mesh strainer (big enough to hold a coffee filter)
- One cup measuring cup for pouring hot solution through filter
- Large clean cooking spoon for removing samples while boiling
- Small clean dark dish (e.g. custard cup) for holding samples
- Clean jar to hold final solution
- Distilled water (in case you over-boil the final solution - see step 14)

Optional Items -this is for a purification step that I found I needed (see step 6 for an explanation). If you decide to do this too, you'll need:

- Two cups granulated activated charcoal (from drug store or pet supply)
- Lab stand with burette clamp (if you have this)
- Funnel (if you have a lab stand; should be big enough to hold folded coffee filters - see step 10)

Step 2Combining baking soda withvinegar

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The first step is the fun part!

Start by pouring all but one cup of the white vinegar into the boiling container (5.5 Qt or larger). (See note about acids below...)
Then, carefully add baking soda to the vinegar, small amounts at a time (no more than a tablespoon). Sprinkle it over the vinegar - don't just dump it in. If you add too much baking soda too quickly, the foam from thereaction may overflow your container.
Stir gently after each addition of baking soda to ensure no unreacted bicarbonate remains.
After adding about a half box of baking soda, you should notice the reaction starting to slow down. At this point you may want to reduce the amount of soda you're adding each time to a teaspoon. When a teaspoon (or less) of baking soda sprinkled over the solution nolonger bubbles instantly but bubbles very sluggishly as it sinks into the liquid, it's time to stop. In my experience, it's taken roughly 12 oz of baking soda to get to this point (about 3/4 of a 16 oz box).

Finally, add the retained cup of vinegar to the liquid. Since judging the stopping point can be difficult to eyeball, I've found it helpful to withhold a small amount of vinegar and add itafter the baking soda reaction almost stops. This way, we err on the side of excess unreacted acetic acid (which will largely boil off) rather than excess unreacted sodium bicarbonate (which will not, and can interfere with crystallization).
(Note on acids: yes yes, I know, we're all taught in science class that you never add X to acid, you add acid to X... Good! Brownie points for rememberingthat! This stuff, however, is a 5% solution of acetic acid, and personally, I'm not too concerned about burning my skin off. If you're too uncoordinated to keep it out of your eyes, wear goggles.)
Step 3What's going on here?

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When you mix baking soda with vinegar, what you're really doing is reacting sodium hydrogen carbonate (more commonly, sodium bicarbonate) with acetic acid. Thosecomponents react, producing sodium acetate and carbonic acid; the carbonic acid immediately decomposes into carbon dioxide gas and water.
Step 4Boiling down the solution

i
The reaction is finished, and we're left with sodium acetate dissolved in water (with a little excess acetic acid). Now, theoretically, all we have to do is boil off the excess water until we get to a metastable supersaturatedstate! Ideally, anyway. I've had difficulty with this part, but let's continue...
Put the solution over medium-high heat and...
Yes, watch it boil. This isn't terribly fun.
You don't want a violent boil, but you are trying to reduce the volume of the solution, so a happy medium rolling boil should be fine.
Take note of the color of the solution when you start your boil... it should be...