Various chemicals were tested for use in a hot pack, and calcium chloride was found to be the most desirable. A very cheap and effective hot pack design was made from a Ziploc bag and duct tape, which insulates the pack and helps keep it warm for longer. Another type of bag, a breakable multi-compartment bag, was considered but was not testable, so the ultimate choice for the container is left to the company's discretion. Ultimately, the proposed hot pack design was found to work extremely well: the reaction is fast and the pack itself is cheap and loses heat quite slowly.
The Chemical Magicians have recently been contacted by a small company seeking to go into the sports medicine market. One area that this company would like to pursue is the hot and cold pack market; upon some investigation, it was found that the hot pack market was smaller and therefore, more effort will be put into this. The company has requested the Chemical Magicians to design a disposable heat pack..
Other than the two obvious considerations of the chemicals involved and the hot pack design, the only other consideration is safety. It is hard to generalize here due to the huge variety of chemicals involved; nevertheless, it is always safe to say that one should wear goggles and gloves at all times and observe standard lab safety procedures. Specific notices for specific compounds are discussed when those compounds are discussed.
[...] In addition, this hand warmer is reusable not exactly the best way to generate revenue for a small beginning company. The next chemical to go was sodium fluoride. This would be practical and release quite a bit of heat upon solvation. However, the problem with this is the safety and disposal. The lowest published lethal dose for humans in LD50 (the amount it takes to kill 50% of those subject) is only 90mg NaF per kilogram of body mass3. In addition, the compound can react with many metals and acids with dangerous yields such as hydrogen gas and hydrofluoric acid (notorious for its ability to dissolve glass). [...]
[...] Ultimately, the choice is left to the company Newton's Law of Cooling Since the Chemical Magicians could not actually observe the hot pack in action for twenty minutes due to a lack of supplies, the temperature after twenty minutes must be calculated using Newton's Law of Cooling: where t is the time, is the temperature as a function of time, Te is the ambient temperature, T0 is the initial temperature, and k is a constant based on the material being observed. [...]
[...] o In case of eye contact with contents: remove any contact lenses. Flush eyes with cold water for at least 15 minutes. Get medical attention. o In case of skin contact with contents: remove contaminated clothing and shoes. Flush skin with plenty of water. Thoroughly wash clothing and shoes before reuse. o In case of ingestion of contents: DO NOT artificially induces vomiting. Loosen tight clothing and articles such as neckties and collars. Call a physician and/or seek medical attention immediately. [...]
[...] This lab test essentially involved comparing the temperature change (ΔT) for these compounds with solutions of equivalent molarity. 100mL of 1.00 M solution was prepared for both compounds using volumetric flasks. For the calcium chloride solution, this involved adding 11.10 g of the solid to the flask, then filling with water. For the calcium acetate solution g was placed in the flask, and the flask was also filled with water. The initial temperature used was the temperature of the water before it was placed in the flask. [...]
[...] Due to time constraints and the difficulty of obtaining subjects to test, this bag was not tested, but is noted here and throughout the lab as a recommendation. Instead, for the laboratory hot pack, an alternative mechanism is to have a clamp on the outside of the bag that holds the calcium chloride pellets in a small pocket of plastic wrap. This will be tightly twisted to disallow leakage. This little package will then be placed inside the Ziploc bag and the clamp will be placed on the Ziploc bag so that it exactly coincides with this opening. [...]
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