Acids and Bases Home Lab “Hot ice” experiment Sodium acetate or hot ice is an amazing chemical you can prepare yourself from baking soda and vinegar. You can cool a solution of sodium acetate below its melting point and then cause the liquid to crystallize. The crystallization is an exothermic process, so the resulting ice is hot. Solidification occurs so quickly you can form sculptures as you pour the hot ice. Materials Baking Soda (söögisooda) 3 tablespoons Vinegar (äädikhape) 30% 100 ml Water 500 ml Saucepan or large beaker Glass, plastic container or small jar Shallow dish Time Required From start to finish, this experiment takes about an hour - hour and half. Once you have the hot ice, you can quickly melt and recrystallize it. !!!The chemicals in this experiment are non-toxic. However, because liquids are boiled, adult supervision is recommended!!! Prepare the Sodium Acetate or Hot Ice 1. Add 500 ml of water to a large saucepan or beaker. Add 100 ml clear vinegar 30% and stir a little. With this you have diluted the 30% vinegar and now you have 600 ml of 5 % acetic acid solution. 2. Add baking soda to the vinegar, a little at a time and stir between additions. The baking soda and vinegar react to form sodium acetate and carbon dioxide gas. Take a picture of this reaction. If you don't add the baking soda slowly, you'll essentially get a baking soda and vinegar volcano, which would overflow your container. When the reaction ends, you will have the sodium acetate solution, but it is too dilute to be very useful, so you need to remove most of the water. Here is the reaction between the baking soda and vinegar to produce the sodium acetate: Na+[HCO3]– + CH3–COOH → CH3–COO– Na+ + H2O + CO2 3. Boil the solution to concentrate the sodium acetate. You could just remove the solution from heat once you have 90-100 ml of solution remaining, but the easiest way to get good results is to simply boil the solution until a crystal skin or film starts to form on the surface. This can take about an hour on the stove over medium heat. If you use lower heat you are less likely to get yellow or brown liquid, but it will take longer. If discoloration occurs, it's okay, even if it is brown it will work. 4. Once you remove the sodium acetate solution from heat, let it cool down a bit at room temperature,and then transfer it to another container(plastic container, class or small jar will do) and immediately cover it with plastic wrap or lid to prevent any further evaporation. You should not have any crystals in your solution. If you do have crystals, stir a very small amount of water or vinegar into the solution, just sufficient to dissolve the crystals . 5. Check the saucepan - if it has some crystals formed on bottom or walls, scrape it and save. You will need a “seed” to start the crystallization process for “hot ice”. 6. Place the covered container of sodium acetate solution in the refrigerator (not into the freezer!) to chill for 40 - 60 min. Activities Involving Hot Ice The sodium acetate in the solution in the refrigerator is an example of a supercooled liquid. That is, the sodium acetate exists in liquid form below its usual melting point. You can initiate crystallization by adding a small crystal of sodium acetate or possibly even by touching the surface of the sodium acetate solution with a spoon or finger. The crystallization is an example of an exothermic process. Heat is released as the 'ice' forms. To demonstrate supercooling, crystallization, and heat release you could: 1. Drop a crystal into the container of cooled sodium acetate solution. The sodium acetate will crystallize within seconds, working outward from where you added the crystal. The crystal acts as a nucleation site or seed for rapid crystal growth. Although the solution just came out of the refrigerator, if you touch the container you will find it is now warm or hot. 2. Pour the solution onto a shallow dish. If the hot ice does not spontaneously begin crystallization, you can touch it with a crystal of sodium acetate (you can usually scrape a small amount of sodium acetate from the side of the container you used earlier or use your saved crystals from the pot). Or just place crystals to the bottom of the dish and pour liquid over them. The crystallization will progress from the dish up toward where you are pouring the liquid. You can construct towers of hot ice. The towers will be warm to the touch. 3. You can re-melt sodium acetate and re-use it for demonstrations. Just melt it in a pot or microwave, cool down again and play with it more. Hot Ice Safety As you would expect, sodium acetate is a safe chemical for use in demonstrations. It is used as a food additive to enhance flavor and is the active chemical in many hot packs. The heat generated by the crystallization of a refrigerated sodium acetate solution should not present a burn hazard, it is just warm to the touch. Possible problems with experiment What to do if crystallization does not occur? This probably means that you still have a lot of water inside sodium acetate solution. Just put it again in a pot and boil some more to reduce the amount of water. Repeat refrigerating and try to form a hot ice sculpture.Repeat until you get desired results if needed. Crystallization starts before you are able to pour it? Warm it, add a little bit of water or vinegar to it and stir. Cool again and try to play with it now. Repeat until you get desired results if needed.
