CHY 124 Phases of Water Lab Report PDF

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Alizah Thayer-Broussard CHY 124, section 0075 2/7/17

Phases of Water Introduction Lab Partner: Sophie Hudson Lab date performed: 2/2/17 Summary: In this lab, we experimentally investigated the amount of energy that is associated with the phase changes of water. By melting the ice (ΔHfus) then evaporating the melted ice (ΔHvap) to 10 mL we were able to gather data to form our own heating curves. We calculated the heat of fusion for each phase from both the phases change curves and the temperature changes during the phase changes. We compared our resulting values (6.15kj/mol and 5.83 kj/mol) and compared it to the accepted value of 6.0 kj/mol. The lab procedure was provided and accessed on the InterChemNet website. [1]  Introduction: This lab was all about exploring the concepts of the heat of fusion and the heat of evaporation. We explored these concepts by detecting the phases of water using a heating/cooling chart. This process important to observing what a solid does while it undergoes both the freezing phase and the melting phase and is especially important in the real world for currency by, the heat of fusion is a huge process in making coins from zinc, copper and other metals.

Evidence Collected from Experiment: Dry ice was melted to a liquid (ΔHfus) and then evaporated into a gas (ΔHvap) by using a bunsen burner, we did this 3 times. In each trial we timed the phase change until water evaporated to about 10 mL, and recorded the temperature of the substance at a given interval. For phase one, we recorded the temperature every 30 seconds, the overall time took about 10 mins. For phase two, we recorded the temperature every 30 seconds again, and for this, the overall time was about 12 mins. Lastly, for phase 3, we decided to record the temperature every 10 seconds while ice was melting considering the temperature changes very rapidly during the ΔHfusion phase. We recorded the temperature every 30 seconds once the water was starting to evaporate, and the overall time for this phase took about 12 mins as well. Below, you can see the heating curves for each phase and the calculations we did for finding the amount of energy needed to overcome the intermolecular forces in the ΔHfusion phase. Trial 1: Unfortunately, we forgot to record the mass after the reaction (mass of ΔHvaporization). So we weren’t able to calculate the ΔHfusion for this phase. However, you can still see the clear curve of when the dry ice starts melting (at about 3 mins) and the rapid change in temperature until the liquid reaches the gas phase (at about 5 mins).

Trial 2: Below you see the phase change for Trial 2. The dry ice starts to melt at about 3 minutes, and then rapidly changes in temperature after the ice melts. Once the liquid reached the gas phase, at about 6 minutes, the temperature stayed around 100 ºC. In this phase, we found that our water evaporated way more than 10 mL, it was around 50 mL instead. We saw that after we took the beaker off the burner, the water evaporated more.

Calculations for Trial 2: Mass of Beaker with Ice: 184.278g Mass of beaker with chip: 106.432g Mass after: 152.93g Evaporated to: 50 mL Mintial - Mfinal= 31.35g nH2O= 31.35g/ 18g/mol= 1.74 moles Heat= 40.674 Jmol-1 x 1.74 moles= 70.77 J Heating rate= 70.77 kJ/mol-1 / 4 mins = 7.7 kJ min-1 ΔHfusion= 1.5min x 17.7kJ min-1 = 26.55 kJ - Multiplied 1.5 min by 17.7kJ because that was the time interval for heat of fusion. 184.278- 106.43= 77.54g 77.54 g/ 18g/mol= 4.32 moles 26.55 kJ/ 4.32moles = 6.15 kJ/mol Percent error: 6.0-6.15/6.0*100= 2.5%

Trial 3: Below you can see the graph for the phase change results during trial 3. For this phase, we tried something a little different, we decided to record the temperature at 10 second intervals while the dry ice was melting, and then go back to 30 seconds once the solid turned into a liquid. This showed the rapid change in temperature from dry ice to liquid a little better, the ice started to melt at around 3 minutes and the temperature changed rapidly until the substance reached 100ºC.

Calculations for Trial 3: Mass of beaker with ice: 197.402g Mass of beaker with chip: 112.196g Mass after: 172.1g Evaporated down to: 30 mL Minitial - Mfinal= MH2O 197.402g - 172.1g= 25.3g nH2O= 25.3g/18 g/mol= 1.41 moles Heat= 40.674 kJmol-1 x 1.41 moles= 57.35 kJmol-1 Heating rate= 57.35 kJmol-1/ 4min= 14.34 kJ/min-1 ΔHfusion= 1.8 min x 14.34 kJ/min-1= 25.812 kJ 197.407- 112.196g= 85.211/ 18= 4.73 moles 25.812 kJ/ 4.73 moles= 5.83 kJ/mol Percent error: 6.0-5.83/6.0*100= 2.8%

Analysis of Evidence: Based on our evidence, we can conclude that our values of heat of fusion were very similar to the accepted value of heat fusion. For phase 2, our result was 6.15 kj/mol and for phase 3, our result was 5.83 kj/mol which both come fairly close to 6.0kj/mol and our percent errors were 2.5% and 2.8%. This lab involved investigating the ΔHfusion and ΔHvaporization, by melting dry ice and recording the temperature changes at a given time interval. The graphs showed the incline from when the dry ice started to turn into a liquid, which was a very rapid process, we measured the heat of fusion through this rapid process by a certain time interval of when the ice actually melts, before it turns into the gas phase. During the phase of sublimation is where we could’ve gained our percent error, we observed that each time we removed the beaker from the heat, the water evaporated a lot more than expected. Claims: We claim that our heat of fusion values were relatively close to the accepted value of the heat of fusion because of the low percent error calculated. We believe that this error was bound to occur, especially within the sublimation process. Many particles could’ve escaped during this process due to the waiting around and probably not the most proper containment of the reaction. Although there was a percent error, our values were pretty close due to the precise calculations and observations done; for example, recording the exact times and temperatures that the ice started to melt and how that provided us with accurate time intervals for the equation.

Works Cited 1. Bruce M. Conservation of Mass. A CORE Learning Cycle Lab Experiment. InterChemNet. h ttp://interchemnet.com/ [ Accessed on Febuary 2, 2017] 2. L. (2017, January 18). Heat of Fusion. Retrieved March 02, 2017, from https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Thermodynamics/State_F unctions/Enthalpy/Heat_of_Fusion...