Mrs. Raihan
Honors Chemistry
25 March 2015
Which salt should be used to make an effective but economical cold pack?

In accordance to the question above, a claim was developed after a series of experiments and observations, Ammonium Chloride, NH4Cl, is the most effectual but also economical ingredient to make a cold pack because it met the requirements of being an inexpensive salt and lowering the mixture’s temperature by 2°c. The claim was proved correctly based off of the quantitative and qualitative data that was taken down during the experiment. To find out whether the salt in the cold back is a good substance or not, the change in enthalpy change, which occurs with the process of dissolution, is also known as the heat of solution. At a constant pressure, the heat of solution is equivalent to the heat lost from the surrounding. For this to happen, the energy is absorbed to break the intermolecular bonds of both the water and the solute, energy is gained in this process. Then, energy is released as attractive forces start to form between the broken ions and water molecules, from here, energy is released. The heat of solution can therefore be an exothermic or endothermic depending on which one is stronger. In this case, the energy absorbed is stronger than the one being released which means it turns cold, an endothermic. So, one can discover if a cold pack is effective by finding the heat of solution then compare to the other salts tested to find out both economically cheap and most effective salt.
Before the investigation commenced, steps were created in order to make sure that everything was going to work out. Using the previously known information, from previous labs made, it was inducted that the following steps would be done to perfect the experiment. First of all the safety equipment was gathered, the materials needed would be gathered and cleaned thoroughly to reduce any human error. The salts that were tested were Ammonium Chloride, Ammonium Nitrate, Magnesium Sulfate and Ammonium Thiocyanate. Then, a calorimeter would be made, two styrofoam cups within one another, a sheet of aluminum between them, a thermometer on top which was struck through the aluminum top to keep the temperature as isolated as possible to have the most accurate information. Then, taking a plastic cup, 30ml of water was measured out then placed into the calorimeter because then 2.5 grams of a salt was measured out. The initial temperature of the water was taken before the ingredients were mixed, immediately after, the temperature was taken down every five seconds for two minutes. The information was recorded in a graph and then averages of the time were taken down so there could be an even information for all salts so there would be no mistake made. The steps above were then repeated twice for each salt, all information recorded into a graph as well. The experiment was conducted in this way to include all of the possible experiments previously done to prove that it was successful, which in the end, based off of the claim, it was correct.

Based off of the guiding question, Ammonium Chloride is the best salt needed to meet both the requirements of being an economically cheap salt and also effective. Ammonium Chloride fell from 21.25°c to 18.65°c, it dropped more than 2°c. The second part of the question asks to choose the cheapest salt, that is still effective which is NH4Cl at $0.0139 per gram. Thus, the salt that meets the guiding question’s needs is Ammonium Chloride because it met the 2°c temperature drop along with an economically cheap price. Using the graphs and tables provided, it is easier to identify the change in temperature for each salt. When one observes NH4Cl, it is easy to comprehend that it is the most efficient one since it has around the same information like the more better, but also expensive ones. Finally, after the information was gathered, the magnitude of heat energy change was found by using the following equation: Q=mc∆T which was then transferred to the heat that the salt let out before dividing it by the number of moles in the solute. The heat of solution was discovered and are as follows: NH4Cl is 9103.29 J/mol,