The Thermodynamics of KNO3 Dissolving in Water PDF

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Retha Ganim General Chemistry Laboratory II The Thermodynamics of KNO3 Dissolving in Water TA: Sadaq Alkhalifa ID: 2710934 Section: #4 28 November 2018

Lab Report: The Thermodynamics of KNO3 Dissolving in Water Introduction: The purpose of this experiment is to determine the KNO3 concentration in a saturated solution from the KNO3 mass and volume of solution. The purpose is to also calculate the equilibrium constant and the delta G for the solubility reaction of KNO3 at each temperature. When potassium nitrate (KNO 3 ) dissolves in water, it dissociates into potassium ions (K) and nitrate ions (NO3 -). Once sufficient quantities of K+ and NO3 - are in solution, however, the ions recombine into solid KNO3 . The concentrations of the ions remain constant; we say the reaction is at equilibrium. This system is called saturated solution where undissolved solid is in equilibrium with its dissolved ions. Entropy is a measure of disorder in a system, the more disordered something is the higher its entropy. Gibbs free energy is the amount of usable energy (energy that can-do work, so NOT heat energy) in a system. Procedure and Data Sheet: Submitted as the carbon-less copy of the pre-lab outline (see attached) and data sheet. Materials Used Hot water bath, 400mL beaker, ring stand, water bath, graduated cylinder, distilled water, potassium nitrate. Results and Discussion The purpose of this experiment is to determine the KNO3 concentration in a saturated solution from the KNO3 mass and volume of solution. Using the balance, we weighted 5.03g of the KNO3. For trial one, the total volume was 6.8 and the temperature when the crystals

formed in the solution was 70.5°C. For trial two, the total volume was 10.2 and the temperature when the crystals formed in the solution was 34.0°C. For trial three, the total volume was 10.65 and the temperature when the crystals formed in the solution was 32.8°C. Finally, for trial four, the total volume was 10.4 and the temperature when the crystals formed in the solution was 31.4°C. The number of moles of KNO3 is 0.05. The concentration of trial one is 7.576. The concentration of trial two is 4.904. The concentration of trial three is 4.695. Finally, the concentration of trial four is 4.807. The Ksp for trial one is 57.40, trial two is 24.02, trail 3 is 22.04, and trial four is 23.11. For delta G, the T,K for trial one is 343.5, trail 2 is 307, trial 3 is 305.8, and trial 4 is 304.4. The lnKsp, trial one is 4.05, trial 2 is 3.18, trial 3 is 3.09, and trial 4 is 3.14. Delta G, trial one is -0.0029, trail 2 is 0.0033, trial 3 is 0.0032, and trial 4 is 0.0032. Conclusion In conclusion, the goal of this experiment was to determine the KNO3 concentration in a saturated solution from the KNO3 mass and volume of solution. The goal was also to calculate the equilibrium constant and the delta G for the solubility reaction of KNO3 at each temperature. Using the balance, we weighted 5.03g of the KNO3. The number of moles of the KNO3 is 0.05. The delta G of each trails were, -0.0029, 0.0033, 0.0032, and 0.0032. The Ksp for each trail was 7.536, 24.02, 22.04, and 23.11. For a reaction to be spontaneous the delta G value must be negative. Delta G is given by dG = dH - TdS So KNO3 dissolving in water is spontaneous at all temperatures. KNO3 when dissolved in water gives K+ and NO3ions. Since bond is broken in the process energy is required to break the bond for which energy should be absorbed. So dissolving KNO3 in water is endothermic process. the entropy of the system increases which makes delta S positive for all temperatures in the hydration of the ions. KNO3 dissolution is endothermic, it absorbs heat....