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Arizona State University *

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Chemistry

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Feb 20, 2024

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Investigation Report for A2Z Written by: Chiara Palacios, Gianni Johnson, Maya Golic, Jazmin Perez Experimental Team includes: Name(s) of Other Member(s) of Your Group Experiment performed on: 09/07/2023

Purpose The purpose of this investigation was to create our own procedures with given materials and values to be able to conduct an investigation according to our own set up. The goals associated with this experiment were to find the rate law, the activation energy, and propose a mechanism that is consistent with the data. To achieve the goals of this experiment, the reaction of HCl with magnesium metal strips was utilized. My group came up with four different variations for four trials. We used a labquest device to graph the pressure while the reaction was happening to create graphs for each trial and collect data on them. Varying a different variable for each trial was useful in seeing how the rate differed and then also helped us determine the rate order as well. The pressure data was collected to calculate the change in the molar concentrations of H 5 produced for each trial so that we could find the rate of the reaction. Using the rate of reaction the rate constant can then be found and with that information, the order of reaction is found and utilized to then find the rate law. The activation energy was then found using the rate constants as well as the varying temperatures from the experiment. The reason for changing the temperature in trial four was to use that to find the activation energy. The information from the activation energy correlates with the rate. For example, the higher the rate the slower the chemical reaction. Methods To achieve the goals for this investigation, the methods we used were calculating the pressure of each reaction of HCI and the magnesium strips. The balanced chemical equation that was utilized to propose a reaction mechanism was: Mg(s) + 2HCl(aq) > H , T MgCl 2(aq). The first trial was our trial in which nothing changed, but the second trial we doubled the amount of magnesium metal used, the third trial the molarity of HCI was doubled, and the fourth trial the reaction was conducted at a lower temperature. The reason for conducting four trials was so that we could be able to see how changing different variables of the reactants would affect the products. The methods used to calculate the change in the products that occurred was through measuring the pressure of the H , &8s. The data that we collected from the data from the labquest gave us our graphs and that was where we found the rates for each trial. Using the rates, we found the order of reactions by comparing the concentrations for specific trials in which the concentrations were constant of HCI to compare the concentrations of Mg. And we did this vice versa for each HCI and Mg. This is how we found the order. Then using that fourth trials concentration we found the Ea using a 1 R(T1 k Arrenius’s Equation: In— 2 = — Tl ). The k ) is the rate constant for the trial 1 2 at the lower temperature and the k was the average of the rate constants for the first 3 trials. This is the information that we reported to A2Z. Materials e Mg strips e (gloves e temperature probe

Scissors 1.0 M HCI 2.0 M HCI LabQuest Pressure Sensor Ice Analytical Balance scale 125 mL erlenmeyer flask 250 mL Beaker Procedure There will be four experiments, and each experiment is different. After gathering all the necessary materials, start with cutting the Mg strips in half. Each experiment will use the same amount of magnesium, while one experiment will double the amount of Mg. When you are cutting the Mg strips make sure they are about the same size. Measure the Mg using an analytical scale for each experiment and record the weight. You will also have each experiment use 1.0M of HCI, while one experiment uses 2.0M of HCI. Fill the erlenmeyer flask with 20 mL of HCIl for each experiment. For experiment 1, cut the Mg strips in half and measure the weight. You will only use one half of the Mg. Next, fill the erlenmeyer flask with 20 mL HCI. You will use the 1.0M of HCI. After the HCI in the Erlenmeyer flask, connect the Labquest and set it to the settings you want it to be. Add the Mg strip into the erlenmeyer flask, and seal it carefully. Make sure you are holding the erlenmeyer flask in an upright position. Notice how the pressure changes throughout the experiment. After 20 seconds, stop recording, save the data, and record the results. Experiment 2 will have similar steps as experiment 1, but instead of using half of the Mg strip, we will double the amount of Mg for this experiment. Cut Mg strips in half carefully with scissors. Make sure that they are cut similarly in an equal size. Record the weight of the Mg strips. Fill the erlenmeyer flask with 20mL of HCI using 1.0M of HCI. After the solution has been created connect the Labquest with the pressure sensor. Make sure to adjust the Labquest settings the way you want it to be. Then, add the Mg into the solution and seal the erlenmeyer flask. Start recording the data in the Labquest. Notice how the pressure changes in the graph. Record for 20 seconds. After 20 seconds, stop recording, and record your results. Experiment 3 everything will be the same except the molarity of HCI. Instead of 1.0M of HCIl, use 2.0M HCI. Cut the Mg strips in half carefully, and record the weight of half of the Mg strip. Then fill the erlenmeyer flask with 20mL of HCl. Make sure to use 2.0M and NOT 1.0 of HCI. After the solution has been created, connect the Labquest to the pressure sensor. Adjust the settings the way you need it to be(change units to atm). After everything has been set up, put the Mg into the solution and seal it carefully. Start recording right away. Notice how the pressure changes. After 20 seconds, stop recording and record your results. Experiments 1-3 will be room temperature, but you will use ice for Experiment 4. Cut Mg strips and record the weight for half of it. Next, fill the erlenmeyer flask with 20

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mL of HCI using the 1.0 M of HCI. After the solution has been created, fill a beaker with ice. After the solution has been created, connect the LabQuest and connect it to the pressure sensor. Once everything is connected, turn on the Labquest. Adjust the settings to the way it should be. After the settings have adjusted, time to do the experiment. Insert Mg strip into the solution in the erlenmeyer flask carefully and seal it. Make sure to hold the erlenmeyer flask in an upright position. Start recording on the Labquest. Notice how the pressure changes. Record for 20 seconds. After 20 seconds, record the data based on the graph that has been created on the Labquest. Measure the temperature of the ice in the beaker. Then, put the flask of the solution in the beaker full of ice and let it sit there in an upright position.Using the Labquest start recording and record it for 20 seconds Notice the pressure changing overtime. Once a graph has been created on the Labquest, record the data. Data Table 1: Concentration of magnesium used in experiments xperimen Viass of Mg | Moles of Mg | Volume o oncentration Q HCI (m of Mg (\V 1 0.0108 | 44 x 10~ 20 0.022 2 0.0231 20 0.0475 9.5 x 10" 3 0.0134 | tc % 10" 20 0.0275 4 00136 | t ¢ % 10" 20 0.028 Table 2: Initial concentration of reactants and measured reaction rates Experiment [Mg] (M) Rate (M/s) 1 1 0.022 (0.0017 2 1 0.0475|0.0037 3 2 0.0275 |0.0041 4 1 0.028 10.0011 Calculations Utilizing the method of initial rates, the following rate law for the given reaction was determined: Table 3: Rate constants of each experiment and the average k at room temperature

1 0.0773 2 0.0779 3 0.0745 Average 0.0766 Table 4: Temperature data and the determined activation energy -mmm——w- T,=? 296.35 T,=? 275 215.92 Sample Calculations: 1. Sample calculation of magnesium concentration for one experiment 44)(10 Mg xm—0.0ZZ 2. Initial conversion of pressure vs. time data to Molarity vs. time data P = conc(RT) P = 0.022 ™ (0.08206 =22 x 296.35 K) = 0.535 ATM 3. Determination of the reaction order of Mg Rate 1 0.0037 n Rate2 ~ 0.0017 2.18=2"n=1 4. Determination of the reaction order of HCI Rate 3 0.0041 n Rate2 ~ 0.0017 241 =2"n=1 5. Determination of the rate constant (k) for one experiment Rate = k[mg]'[HCI]" k(0.022)(1) = 0.0017 k =0.0773 6. Calculation of the average of the rate constant at room temperature 0.0773+0.0779+0.0745 0.0766 3 - [

7. Calculation of activation energy using Arrhenius two-point equation 1y 0039 Fa R 8314 008206 \ 29635 275 Ea = 215.92 J/mol Discussion and Conclusions Our team achieved the overall goal of exploring the kinetics of the reaction between HCI and a magnesium metal. Therefore, it helped us determine the rate law of a given reaction Mg(s) + 2HCl(aq)—H?2(g)+MgClI2(aq), the activation energy, and any possible mechanisms that remained consistent with the experimental data that our team concluded as part of our result. After our team designed the experiment and collected the data, we constructed four consistent graphs. Analyzing the applicable data, we noticed that all four graphs show a consistency of an increasing reaction with certain variables affecting the reaction over a certain amount of time. The increased reaction remained consistent for the most part, however there were minimal spikes within the graphs of one and two, which can be caused from the reaction itself or outside variables in how the experiment was handled or completed. These spikes are not alarming as our data perfectly corresponds to our experiment and the consistency of all points persists. Unequivocally, our constructed experiment transpired to be successful in fathoming the mechanisms of an experiment that allows us to conclude our report. Our team was able to ascertain that the Mg is a first order reactant in the given reaction, and that HCl is a second order reactant, forming a third order reaction taking everything into account. Additionally, by comparing two parts of our trials, specifically the results of our experiment three and four, which were both completed and tested with disparate temperatures, our team was able to demonstrate the reaction’s activation energy, which happens to be Ea = 215.92 J/mol. Since there are three molecules in the reactants' place, we can easily determine that the reaction mechanism of this specific reaction is termolecular given HC] and Mg. Taking into consideration, this reaction mechanism can be theorized as Mg + Cl2 - MgCl2 (fast) and 2HCl - H2 + Cl2 (slow) Our group concluded that this is the reaction process because we know that before the CI can react with the Mg, the HCI must be broken down into its constituents. Assuming that the first step is the rate regulating step since the magnesium is always available in the reaction but is dependable on the rate of which can only be reacted with as quickly as the CI2 can be provided to it. The significant errors that occurred were mainly caused by human and procedural errors. Following the experiment’s procedures, most mistakes encompassed measuring the pressure, but not when it was presumably measured within our variable, the beaker of ice. Our team conducted another trial for one out of our four trials for our reactions because of the inaccuracy of the graph for trial three. The reasoning was unknown, but

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our suggested error could have been because of the size of the magnesium metal strip that we cut in half about three different times to try and get an accurate estimation of mass. Since all magnesium metal strips had to be the same size and mass, we tried to cut the metal strip in an equal size comparing it to the other strips. A further possible assumption as to why our third graph didn’t show a consistency of data is because the reaction ran way too fast. These are just some of the conclusions we proposed collectively as a possibility to why our third trial didn’t correspond to the other graphs. If this experiment or investigation was repeated, we could eliminate the number of errors that were made by repeating the accurate measurements and taking the same mass that is at least exact or almost exact to the mass sample sizes that we had sampled. As for the carelessness of mistakes causing our group to miss key details in the procedure, this can be prevented by reading the procedure as we go to ensure we don’t miss any important steps. As each step is highly important in receiving precise and feasible results. For the reason that H2, hydrogen, is expensive to produce and is not readily available, hydrogen is less common in the environment than other gasses. For its manufacturing, procedures like water electrolysis are necessary. This technique is time costly and highly expensive. Using an emission-free energy source would be counterproductive because this method is expensive and produces more carbon dioxide, thus damaging our quality of life. This gas is also very combustible and an explosive chemical that cannot be easily transferred from one location to another, making it even more unreliable. Even if it was to be cautiously transferred from one place to another, there are not many locations to refill. Hydrogen gas burns in the air in a wide range of concentrations, ranging from 4 to 75%. Other non-renewable sources of energy, such as coal, oil, and natural gas, are frequently utilized to separate it from oxygen. While the goal of converting to hydrogen is to eliminate the usage of fossil fuels, fossil fuels are still frequently used to manufacture hydrogen fuel. When it comes to oil, it can be transported via pipelines. When it comes to coal, it is simply transported on the backs of trucks. When it comes to hydrogen, even transferring little amounts is prohibitively expensive. Transporting and storing such a material is deemed impracticable for this reason alone. To this day, gasoline is still frequently used. And, as of now, there is no infrastructure that can sustain hydrogen as a fuel. This is why even thinking about replacing fuel becomes too expensive. Since there is no infrastructure currently, just transporting hydrogen itself will also affect exceedingly expensive prices. Although hydrogen cells are increasingly utilized to power hybrid vehicles, it is still not a viable fuel source for everyone. Until technology that makes the entire process more simpler is developed, hydrogen energy will remain a costly choice and unsubstantial when it comes to our environment. Renewable energy sources such as solar and wind can be used to generate hydrogen energy, making it a more environmentally friendly and an alternative option to overcome these limitations. Why make our environment worse by representing a new fuel source that uses hydrogen gas, when our environment is already coming to a grapple to maintain or develop? If the process was straightforward, everyone would be doing it with relative ease, but it isn't. Therefore, A2Z Products should not continue pursuing H2 as an alternative fuel source as it has very unreliable sources.

Appendix A: Experiment 1 9.80E-01 y =0.0017x + 0.9657-" ¢ RZ = 05!5.76‘ 9.76E-01 L 9.78E-01 9.74E-01 * 9.72E-01 9.70E-01 9.68E-01 9.66E-01 9.64E-01 Experiment 2 1.02E+00 y =0.0037x + 0.9808 1.01E+00 RZ=0.9669 .. ® 1.01E+00 [ 1.00E+00 9.95E-01 9.90E-01 T : 9.85E-01 ! 9.80E-01 9.75E-01

1.01E+00 1.01E+00 1.00E+00 9.95E-01 9.90E-01 9.85E-01 9.80E-01 9.75E-01 L. 9.70E-01 9.95E-01 9.94E-01 9.93E-01 9.92E-01 9.91E-01 9.90E-01 9.89E-01 9.88E-01 9.87E-01 9.86E-01 985601 & 9.84E-01 Experiment 3 3 4 5 Experiment 4 y = 0.0041x + 0.9738 .9 R?=0.9994."" 6 7 8 y=0.0011x+0.9853.4 R? =0.9953"" 6 ? |

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Appendix: B - Original data E Experiment 1 Experiment 2__/__,_ Mass of Mg (g) 0.0]0% & Mass of Mg (g) e B/ ] Concentration of HC| (M) [.OM*E Concentration of HCI (M) __Ilﬂ__‘ Volume of Hc| (L) Volume of HCI (L) Temperature (°C) Temperature (°C) j Time (s) Pressure (atm) Time (s) Pressure (atm) 0 0.0 D Sl 2 0 qw%g 2 Q(I :*U»; e © 4 0 .2147 - 6 (0.915% G 0% 8 0“?7<€| 8 | Opg? 10 0.9517 10 e L 12 0.954% 12 i 14 0.9%1¢ 14 W WG 1e 04956, 16 XL 18 (). 49119 18 20 LD 20 R 221 o) Experiment 3 Experiment 4 Mass of Mg (g) 0.0 1% Mass of Mg (g) 0.6\ Concentration of HCI (M) 7.0 N\ Concentration of HCI (M) ). OWN ‘ Volume of HCI (L) 5 Volume of HCI (L) Temperature (°C) Temperature (°C) Time (s) Pressure (atm) Time (s) Pressure (atm) 0 0. 94739 0 0 ag5? 2 0. 482\ 2 0.4875 4 0.S90( 4 0. asaq 6 0.9 98U 6 0.Qq 272 8 1. 00k 8 O ag3s 10 LG1Y8 10 G = = 2 | eceay, | i |.074( 14 \ 16 L0374 16 _W 18 Bzl B | Voes 20 05822 *\ 10