Deicer Lab Report - 2nd Submission

Evaluating Deicer (KCl) By Finding Its Freezing Point of Depression, Enthalpy of Dissolution, and Cost and Environmental Impacts ABC Feb 28 (Spring 2022)

I. Abstract The main objective of this lab was to evaluate how good potassium chloride (KCl) is as a decider by finding its freezing point of depression, enthalpy of dissolution, and comparing its cost per unit and environmental impacts with other deicers (such as NaCl, MgCl 2 , and CaCl 2 ). The freezing point of depression was determined by finding out the freezing temperature of different solutions of KCl in DI water with different molalities. It was found that KCl decreases the freezing point of water. Also the calculated van’t Hoff factor of KCl from the experiment was 5.33, with a percent error of 188.11%. KCl’s enthalpy of dissolution was calculated through experiments with a self-made calorimeter. The calculated enthalpy of dissolution for KCl was calculated to be 10.72kJ/mol, with a percent error of 37.82%. According to some online sources, the cost per unit of this deicer is around $4.99 per 9 ounces of KCl. It was also found that the use of KCl can sometimes even be beneficial for plant growth but may also harm the environment through ways such as entering the groundwater systems. II. Introduction Snow and extreme weather, such as in Minnesota, causes icy roads and sidewalks and can cause a lot of danger for cars and pedestrians; therefore, deicers are often used. Deicers are materials (often salts) used to decrease the freezing point of snow and prevent ice from forming. 1 Many types of deicers can be used, such as KCl, NaCl, MgCl 2 , and CaCl 2 , but not all types of deicers have the same effectiveness as a deicer and some may be more harmful for the environment compared to others; therefore, it is important to find a deicer that is effective, and cheap, yet is least harmful for the environment. There have 1 How salt works and overview of deicing materials. https://stormwater.pca.state.mn.us/index.php/How_salt_works_and_overview_of_deicing_chemicals (accessed Feb 16, 2022)

A calorimeter was created by stacking two foam cups and a piece of cardboard with a hole cut through just enough to fit the temperature probe as the lid. Another temperature probe was plugged into a computer and into Logger Pro. Another ice bath was also set up and an electric hot plate was plugged in. In two beakers, 30ml of DI water was measured out and poured into those beakers. One beaker was heated on the hot plate, and one beaker was chilled in the ice bath until the temperature difference between the two beakers was around 60°C to 70°C. The temperature of both beakers were measured and they were both immediately poured into the foam calorimeter and the temperature probe was kept inside it. When the temperature of the water stabilized on the Logger Pro program, the number was recorded again. The procedure was repeated two extra times. The data collected was used to calculate the specific heat of the calorimeter (C cal ). Three masses of potassium chloride were collected again (0.745g, 0.373g, and 0.186g). 30ml of DI water was measured and poured into the calorimeter and its temperature was recorded. KCl was added into the calorimeter and stirred up well with a glass stirring rod. After the temperature of the solution stabilized, the temperature was recorded. The procedure was repeated for the other two samples of KCl. The van’t Hoff factor, enthalpy of dissolution, cost, and environmental impacts of KCl was then compared to other chemical deicers, such as NaCl, MgCl 2 , and CaCl 2 to evaluate how good KCl is as a deicer. IV. Results The required mass of KCl that was needed in order to get the desired molalities to get solutions of desired molalities was calculated by manipulating equation 1.

Molality = moles solvent/kilograms solution Equation 1 The temperature at which different KCl masses in 5ml of DI water freezes (turning from a liquid into a solid) was recorded and shown in table 1. It can clearly be seen that when KCl was added, the freezing temperature of water was reduced. Table 1: Freezing point of different KCl molalities. Trial # KCl mass Molality T f (solution) ΔT f = T f (solvent) - T f (solution) 1 0.745g 1.0 -11.5 °C 11.5 °C 0.373g 0.50 -4 °C 4 °C 0.185g 0.25 -3.6 °C 3.6 °C 2 0.745g 1.00 -10.6 °C 10.6 °C 0.373g 0.50 -7.7 °C 7.7 °C 0.185g 0.25 -3.1 °C 3.1 °C The freezing point of depression of KCl and its corresponding molality times pure water’s molal freezing point of depression constant was shown in figure 1. The linear regression line and its coefficient of determination (R 2 ) can also be seen in the figure. The slope that can be seen in figure 1, which is the van’t Hoff factor of KCl, was found to be 5.53. The coefficient of determination for the linear regression line was 0.893.

Trial 1 Trial 2 Trial 3 Cold Hot Cold Hot Cold Hot Initial 15.00 °C 90.00 °C 12.50 °C 84.60 °C 11.00 °C 89.20 °C Final 50.15 °C 47.20 °C 47.70 °C Change 35.15 °C -39.85 °C 34.70 °C -37.40 °C 36.70 °C -41.50 °C C cal 16.78J/K 9.76J/K 16.42J/K Average C cal 14.32J/K C cal = -(m hot c hot T hot + m cold c cold T cold )/ T cal Equation 3 ∆ ∆ ∆ The initial temperature of water and final temperature of the KCl and 30ml of DI water solution can be seen in table 3. The heat released in the reactions (q rxn ) are calculated using equation 4. The enthalpy of dissolution for the samples were calculated to be 10.72kJ/mol with equation 5. Table 3: Temperatures of 30ml of DI water before and after adding potassium chloride Initial Final Change q rxn H rxn ∆ KCl (0.7455g) 21.5 °C 20.8 °C 0.7 °C 97.90J 9.79kJ/mol

KCl (0.3727g) 21.4 °C 21.0 °C 0.4 °C 55.94J 11.19kJ/mol KCl (0.1863g) 21.5 °C 21.3 °C 0.2 °C 27.97J 11.19kJ/mol q rxn = -(C cal T + m H20 C H20 T) Equation 4 ∆ ∆ H rxn = q rxn /moles salt Equation 5 ∆ Compared to the actual value of KCl’s enthalpy of dissolution, which was found to be 17.24kJ/mol through online sources, the percent yield was calculated using equation 6 below 3 . Percent error = |(observed value - expected value)/expected value|*100% Equation 6 Percent error = (10.72 - 17.24)/17.24*100% = 37.82% V. Discussion Rock salt was added to the ice bath when experimenting with the freezing point of different molarities of KCl since it can lower the temperature of the ice bath. As can be seen in table 1, the freezing temperature of the DI water decreased as the molality increased and this trend can also be observed in figure 1. This indicates that KCl can be used as a deicer and the more KCl is used, the lower the freezing point of water will be. 3 Chieh, C. Hydration https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Mod ules_(Physical_and_Theoretical_Chemistry)/Thermodynamics/Energies_and_Potentials/Enthalpy/Hydration (accessed Feb 18, 2022).

heat from the environment. Foam cups were used as a calorimeter due to being a great insulator, which helps it drastically reduce the amount of heat from entering or escaping the system. 6 However, since the calorimeter is not ideal, some energy from the system will be lost so the calorimeter constant must be calculated. The calorimeter constant shows the specific heat of the calorimeter and its heat conductivity and this constant must be taken into account when calculating KCl’s enthalpy of dissolution. 7 Potassium chloride’s average enthalpy of dissolution was calculated to be 10.72kJ/mol based on table 3. According to literature, having a positive enthalpy means that the dissolution of KCl is an endothermic reaction and that heat is absorbed from the surroundings and in this case was the water. For instance, in this experiment, the enthalpy of dissolution for KCl was found to be 10.72kJ/mol, this means that for every mol of KCl dissolving in water, 10.72kJ of energy or heat is absorbed from the environment into the system. For deicers, having a lower enthalpy of dissolution means that the substance takes in more heat from the surroundings and can lower the temperature of the water and as a result lower the freezing point of ice more. The experimental value of KCl’s enthalpy of dissolution was calculated to have a percent error of 37.82%. A possible reason for this error was not stirring the solid KCl in the DI water enough, causing the chemical to not be able to fully dissociate in the water. Another possible reason that could have resulted in a lower value is error in making and calculating the calorimeter constant. Styrofoam is a great insulator, which can keep heat from escaping the cups; however, errors in making 7 Calorimeter Constant. http://sites.science.oregonstate.edu/~gablek/CH362/calorim2.htm (accessed Mar 15, 2022) 6 Calorimeters and Calorimetry. https://www.physicsclassroom.com/class/thermalP/Lesson-2/Calorimeters-and-Calorimetry#:~:text=The%20role%2 0of%20the%20Styrofoam,water%20and%20the%20surrounding%20air . (accessed Mar 15, 2022)

sure the cardboard lid of the calorimeter is working the same can affect the calculated calorimeter constant. Both the van’t Hoff factor and enthalpy of dissolution can be used to evaluate a chemical’s goodness as a deicer. When comparing the actual values of KCl’s van’t Hoff factor to that of NaCl, MgCl 2 , and CaCl 2 , it was seen that the van’t Hoff factor was lower, indicating that KCl is a worse deicer. Also, when comparing the actual theoretical values of KCl’s enthalpy of dissolution with those deicers, that of KCl can be seen to have a much higher value, which further supports the idea that KCl is a worse deicer. For instance, CaCl 2 has an enthalpy of dissolution of -80kJ/mol, which means that the dissolution of this substance is exothermic and heat is released during the reaction, increasing the temperature of water; therefore, more heat is needed to be taken out of the system to freeze the water and the freezing point is of water is decreased. 8 The cost and environmental impacts of KCl were also considered. It was found on an online source that the cost of solid KCl was $4.99 per 9 ounces and, compared to other deicers (such as NaCl), is much more expensive. It was also found that KCl can be bad for the environment for several reasons. One reason was that chlorine-based salts can corrode metals, such as on cars or the railings of roads, and this can potentially be dangerous. 9 The environment can also be harmed through KCl seeping into the soil next to roads, lowering the alkalinity of soil and harming trees and plants. 10 However, since 10 Environmental impacts of road salt and other de-icing chemicals. https://stormwater.pca.state.mn.us/index.php/Environmental_impacts_of_road_salt_and_other_de-icing_chemicals (accessed Feb 19, 2022) 9 Urea and Potassium Chloride. https://meltsnow.com/products-old/urea-and-kcl/#:~:text=This%20product%20might%20be%20called%20red%20p otash%20as%20well.&text=In%20deicing%20terms%2C%20we%20tend,it's%20ok%20but%20not%20great (accessed Feb 19, 2022) 8 Free energy and solubility. https://virtuallaboratory.colorado.edu/CLUE-Chemistry/chapters/chapter6txt-4.html#:~:text=If%20we%20look%20 up%20the,the%20system%20to%20the%20surroundings . (accessed Mar 15)

real-life applications such as the practice of accuracy, since in this lab errors in weighing out the incorrect amount of KCl can dramatically impact the collected results. For non-scientists at home, the same accuracy is needed for chemical treatments, such as pouring liquid fertilizer into a fish tank. VII. References 1. How salt works and overview of deicing materials. https://stormwater.pca.state.mn.us/index.php/How_salt_works_and_overview_of_deicing _chemicals (accessed Feb 16, 2022) 2. McElroy, A. D.; Blackburn, R. R.; Hagymassy, J.; Kirchner, H. W. Comparative study of chemical deicers https://onlinepubs.trb.org/Onlinepubs/trr/1988/1157/1157-001.pdf (accessed Feb 18, 2022). 3. Chieh, C. Hydration https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_ Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Thermodynamics/ Energies_and_Potentials/Enthalpy/Hydration (accessed Feb 18, 2022). 4. 13.9: Solutions of Electrolytes. https://chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_General_Chemistr y_(Petrucci_et_al.)/13%3A_Solutions_and_their_Physical_Properties/13.09%3A_Solutio ns_of_Electrolytes (accessed Feb 19, 2022) 5. Changing State: Freezing https://www.middleschoolchemistry.com/lessonplans/chapter2/lesson4 (accessed Mar 18, 2022)

6. Calorimeters and Calorimetry. https://www.physicsclassroom.com/class/thermalP/Lesson-2/Calorimeters-and-Calorimet ry#:~:text=The%20role%20of%20the%20Styrofoam,water%20and%20the%20surroundi ng%20air . (accessed Mar 15, 2022) 7. Calorimeter Constant. http://sites.science.oregonstate.edu/~gablek/CH362/calorim2.htm (accessed Mar 15, 2022) 8. Free energy and solubility. https://virtuallaboratory.colorado.edu/CLUE-Chemistry/chapters/chapter6txt-4.html#:~:te xt=If%20we%20look%20up%20the,the%20system%20to%20the%20surroundings . (accessed Mar 15) 9. Urea and Potassium Chloride. https://meltsnow.com/products-old/urea-and-kcl/#:~:text=This%20product%20might%20 be%20called%20red%20potash%20as%20well.&text=In%20deicing%20terms%2C%20 we%20tend,it's%20ok%20but%20not%20great (accessed Feb 19, 2022) 10. Environmental impacts of road salt and other de-icing chemicals. https://stormwater.pca.state.mn.us/index.php/Environmental_impacts_of_road_salt_and_ other_de-icing_chemicals (accessed Feb 19, 2022) 11. Potassium chloride: impacts on soil microbial activity and nitrogen mineralization. https://www.scielo.br/j/cr/a/SM8P4qKRKmMJMCzbk9fzwzC/?format=pdf&lang=en#:~: text=Potassium%20chloride%20(KCl)%20is%20the,et%20al.%2C%202014 (accessed Feb 19, 2022) 12. Handbook of Test Method for Evaluating Chemical Deicers. https://onlinepubs.trb.org/onlinepubs/shrp/SHRP-H-332.pdf (accessed Feb 19, 2022)