CHEM 1412 DC Kinetic Observable Change of Color as Reaction Lab Report

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CHEM 1412

Dallas College

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Objectives: 1. To determine the order of a reactant in a chemical reaction. 2. To generate the rate law and determine the rate constant at room temperature for a reaction. Materials: ● ● ● ● ● ● ● ● ● ● Zinc metal strip 3 M HCl (22 mL) 10 mL graduated cylinder 100 mL graduated cylinder 250 mL Beaker Test tubes (3) Test tube clamp Test tube rack Marker pipette ● ● ● ● ● ● 250 mL Erlenmeyer flask One hole stopper for flask 3 inch rigid tubing Long flexible tubing Pot with handle (student provides) String or rubber band (student provides) ● Plastic wrap (student provides) ● Distilled water (student provides) ● Sand paper Introduction: Chemical kinetics is the branch of chemistry that is concerned with the study of the rates of chemical reactions and their mechanisms. The rate is the speed at which a reaction occurs and the mechanism is the process by which it proceeds. If you travel from Dallas to Waco you will be traveling at a certain speed, or rate. Likewise, a chemical reaction has a speed or rate which tells you how fast or slow that reaction is. Going back to your Waco trip, one can ask: how are you going to get there? The answer to this provides your means (or mechanism) of transportation. For instance you can ride a horse, you can drive, or you can fly. Mechanisms of chemical reactions are the step by step process of how the atoms rearrange and are very difficult to figure out. We will NOT be figuring out a reaction mechanisms in this lab. This lab will determine the order of reaction of a reactant in a chemical reaction. Background: Reaction Rate The rate of a chemical reaction can be expressed as a change in concentration of either a reactant or product over a time period. Rate Law The rate law for a chemical reaction is an equation that links the reaction rate with the concentrations (or pressures) of the reactants. By measuring how the rate changes with reactant concentration we can experimentally figure out the rate law. Online CHEM 1412 Chemical Kinetics The rate law describes a predictable behavior of the speed (or rate) of the reaction with respect to the reactant concentrations. The rate law is always true for a given reaction at a certain temperature. Consider the following hypothetical reaction: A + B → Products In general, the rate law can be written as Rate = k [A]m[B]n Where ● ● ● ● k is the rate constant m is the order of the reaction with respect to A n is the order of the reaction with respect to B The sum m + n is the overall order of the reaction If m = 1, the reaction is said to be first order in [A]. If m = 2, then the reaction is second order in [A]. If the rate is independent of [A], then the reaction is said to be zero order with respect to [A]. The rate constant, k, is temperature dependent and will vary at different temperatures. (We will perform the reaction at room temperature.) For example, the rate law of the specific reaction 2NO2 + F2 → 2NO2F was experimentally determined to be: Rate = k[NO2][F2] The reaction is first order in both [NO2] and [F2] and second order overall. In this experiment, you will study the reaction of solid zinc metal with hydrochloric acid. The reaction is: Zn (s) + 2HCl(aq) → ZnCl2(s) + H2(g) The reaction order for HCl can be determined by monitoring the rate of the reaction. We will monitor the rate by measuring the formation of hydrogen gas as it fills a graduated cylinder. We will measure the gas in units of mL. Even though we are monitoring the reaction by the formation of the hydrogen gas, the rate of the reaction will depend on the concentration of hydrochloric acid according to the rate law. The rate law for this reaction is Rate = k[HCl]m Where m is the order with respect to HCl and k is the rate constant. The values of m and k must be experimentally derived. They cannot be figured out just from the stoichiometry of the reaction. In this experiment we will determine m and k by performing three trials of the reaction with three different concentrations of HCl and zinc. The initial rates can be measured by the production of H2 gas. Notice the solid Zn does not appear in the rate law and Dallas College CHEM 1412 online Chemical Kinetics pg 2 Online CHEM 1412 Chemical Kinetics therefore does not affect the reaction rate. The reaction rate will change with differing concentrations of HCl. Procedure: Part I: Preparation Caution: Always wear gloves when working with acids or bases. 1. Label three test tubes: 3.0 M HCl, 2.0 M HCl, and 1.5 M HCl. 2. Do the following: Be careful with the HCl as you will need to use the remaining HCl for the other labs. a. Transfer 10.0 mL 3.0 M HCl stock solution to a test tube labeled 3.0 M HCl. b. Take 6.7 mL of 3.0 M HCl stock stolution and put into the 10 mL graduated cylinder. Add distilled water to the 10.0 mL mark. Transfer to test tube labeled 2.0 M HCl. c. Take 5.0 mL of 3.0 M HCl stock solution and put into the 10 mL graduated cylinder. Add distilled water to the 10.0 mL mark. Tranfer to test tube labeled 1.5 M HCl. 3. Carefully insert the rigid glass tube into the rubber stopper. Be careful, as the tube is made of glass. If needed, dip the end of the tube in water as a lubricant to help ease it into the stopper. Caution: Be careful not to break the glass tubing as you work with it. It may be difficult to insert it in the rubber stopper hole without breaking it. Hold the glass tubing close to the end that goes in the stopper to minimize breakage and work the tubing in gently. 4. Hold the end of the long plastic flexible tubing and carefully work it over the other end of the rigid tubing. Be sure to hold the rigid glass tubing close to the end that is being inserted into the flexible tubing. 5. Fill a large pot with water. Dallas College CHEM 1412 online Chemical Kinetics pg 3 Online CHEM 1412 Chemical Kinetics 6. Fill the 100 mL graduated cylinder completely with water. Seal the top of the cylinder with plastic wrap. 7. Invert the cylinder into the pot of water so that the cylinder remains completely full of water. Be sure that there is not an air gap at the top in the cylinder. 8. Remove the plastic wrap. 9. Clamp the graduated cylinder with the test tube clamp. 10. Secure the graduated cylinder to the pot. Use a string or rubber band to strap the handle of the test tube clamp to the handle of the pot. 11. Insert the long flexible plastic tubing extending from the rigid glass tubing into the graduated cylinder. This will allow the gas to be collected inside the graduated cylinder as shown in the picture below. Be sure that the flexible plastic tubing is completely inside the cylinder and will not come out. 12. In the 250 mL beaker add 200 mL of tap water and set this aside. 13. Bend the zinc strip in half so that it will lay flat in the bottom of the flask. You may also cut the metal in half, but do not cut it into small pieces, as it will be hard to weigh. 14. Put the zinc strip in the bottom of the Erlenmeyer flask. Part II: Performing the Reaction 1. At time zero, add 10.0 mL 3.0M HCl solution to the zinc strip in the Erlenmeyer flask and quickly stopper the flask. 2. Shake the flask gently so that the HCl will come in contact with the zinc. Dallas College CHEM 1412 online Chemical Kinetics pg 4 Online CHEM 1412 Chemical Kinetics 3. Record time and volume every 30 s until 70.0 mL H2 is collected in the graduated cylinder. The H2 gas will displace the water in the graduated cylinder. 4. When 70.0 mL of gas are collected the trial is over. Record this time. 5. Clean up the apparatus in preparation for Trials 2 and 3: Remove the stopper from the flask and dump the contents of the flask into the small 250 mL beaker with the 200 mL of water. (This will dilute the acid so that clean up is less hazardous.) 6. Take the 250 mL beaker to the sink and with the water running, carefully pour out the solution leaving the zinc strip. Flush the solution down the drain with plenty of water. Caution: Do not put your hand directly into the beaker to remove the zinc strip. Remember that the beaker does contain the hydrochloric acid solution. 7. Rinse the Erlenmeyer flask and the zinc strip well. Dry and sand off any black residue on the zinc strip. Put the zinc strip in the bottom of the Erlenmeyer flask. 8. Refill the graduated cylinder with water and set up the apparatus for two more trials. 9. Repeat Part II Steps 1-7 using the 2.0 M and 1.5M HCl solutions. 10. Save the zinc strip for a later experiment. WASTE DISPOSAL: Dispose of all chemical waste down the sink with plenty of water. Sample Calculations: 1. I am studying a reaction that produces CO2 gas. I perform the reaction and collect 80.0 mL of the gas and it takes me 185 seconds to collect this 80.0mL. What is the rate of this reaction? Rate = change in the amount of product/change in time Rate = 80mL-0mL/185s-0s = 0.43mL/s Dallas College CHEM 1412 online Chemical Kinetics pg 5 Online CHEM 1412 Chemical Kinetics 2. For a reaction X + Y → Z the following data was obtained: Trial 1 2 3 4 [X] 0.050 0.050 0.025 0.050 [Y] 1.0 2.0 2.0 4.0 Rate of formation of Z (M/s) 0.20 0.40 0.10 0.80 Find the value of m in the rate law of this reaction: Rate = k[X]m[Y]n a. Look in the table for two trials where Y is constant and X is varied. This would be Trials 2 and 3. We see that when X is doubled, the rate is quadrupled. The value of m is 2 in order for this to be true. But to prove it we can do the following. When we fill in the data for the two trials into the rate law we get the following: Trial 2: 0.40 M/s = k (0.050M)m(2.0M)n Trial 3: 0.10 M/s = k (0.025M)m(2.0M)n We can take these two equations and divide the bottom into the top: 0.40 𝑀/𝑠 = 𝑘(0.050𝑀 𝑋)^𝑚(2.0𝑀 𝑌)^𝑛 0.10 𝑀/𝑠 = 𝑘 (0.025𝑀 𝑋)^𝑚(2.0𝑀 𝑌)^𝑛 Simplifying gives us: 4 = 2m We can see that in order for the equality to hold, m must equal 2. Or if you insist on doing it Algebraically: log 4 = log 2m log 22 = log 2m 2log 2/log 2 = m 2=m The order of the reaction with repect to X is 2. This reaction is second order with respect to X. b. Find the value of n in the rate law for this reaction. Look in the table for two trials where X is constant and Y is varied. This would be Trials 1 and 2. We see that when Y is doubled, the rate is also doubled. The order of this reaction with respect to Y is 1. This reaction is first order with respect to Y, or n = 1. ● What is the rate law of this reaction? Rate = k[X]2 [Y] Dallas College CHEM 1412 online Chemical Kinetics pg 6 Online CHEM 1412 Chemical Kinetics ● What is k? Using one of the trials (generally it does not matter which), fill in the values and solve for k. Include the units! The following calculation uses Trial 1 data from the table. Rate = k[X]2[Y] 0.20M/s = k (0.50 M)2 (1.0M) 0.20 M/s = k 0.25 M2 1.0M 0.20 M/s = k 0.25 M3 k= k= 0.20𝑀/𝑠 0.25 𝑀3 0.80/𝑠 𝑀2 Dallas College = 0.80 M-2s-1 CHEM 1412 online Chemical Kinetics pg 7 Online CHEM 1412 Chemical Kinetics Kinetics Lab Report Sheet Name: Partner (if applicable): Observations of reaction: Data Tables: Trial 1 Time 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 630 660 690 mL H2 Dallas College Trial 2 Time 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 630 660 690 mL H2 Trial 3 CHEM 1412 online Chemical Kinetics Time 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540 570 600 630 660 690 mL H2 pg 8 Online CHEM 1412 Chemical Kinetics Trial [HCl] M 1 3.0 2 2.0 3 1.5 Time taken to produce 70mL of H2 Rate of reaction (ml H2/s) Fill in the table below (show work). You will determine k from each of the trials and then average them together. Order of HCl in rate law: m = Rate law: Rate = Rate constant trial 1: k1 = Rate constant trial 2: k2 = Rate constant trial 3: k3 = Average rate constant k= Conclusion Dallas College CHEM 1412 online Chemical Kinetics pg 9 Grading Rubric for NLC CHEM Lab Reports Lab Report Sheet The following is a breakdown of the different parts of the Lab Report for all labs except Experimental Design. The Experimental Design lab has a slightly different format as outlined in the next section. 1. Performing the lab and recording data: ~60 points (may vary). There may also be some pertinent calculations. 2. Questions and problems: ~ 20 points (may vary). These will be at the end of the Report Sheet. Show your work. 3. Conclusion: 20 points. Not all North Lake labs require a written conclusion, this varies from course to course. Currently only CHEM 1407 and CHEM 1412 online are required to write conclusions for every lab. The 20 points for the conclusion replaces the 20 points lab quiz. The Experimental Design Lab does not have a quiz and for this lab, everyone has to write a conclusion (see breakdown for Experimental Design Lab below). The conclusion should be succinct and NOT a reiteration of the procedure. It should have the following: ➢ Thesis statement or Explanation of the Lab – one sentence that explains what the lab’s purpose is. ➢ Results and Conclusion - experimental data and analysis to either support or disprove the thesis. ➢ Error Analysis Please see the rubric below for further details. Lab Report Sheet - Experimental Design The following is a breakdown of the different parts of the Experimental Design Lab Report. 1. Unknown identification/answering the specific question – 10 pts There may be calculations that will be checked for accuracy. 2. Procedure – 20 points Must write a step by step procedure that anyone can follow and get consistent, reproducible results. Make sure that the procedure is clear and unambiguous. This necessitates attention to detail, do not leave out any steps. Do NOT copy and paste a procedure from one of your labs or from other sources (this is plagiarism). Put it in your own words. 3. Conclusion - 20 points. See rubric below. 4. Case Study – 25 points Read the case study and answer the question posed. Document your position from credible sources. ➢ 10 pts- thesis statement ➢ 10 pts – argument ➢ 5 pts – citations/bibliography 5. Team Work 25 pts – Please answer the questions honestly. There is no right or wrong answer. No points will be deducted unless you do not answer the question. We are interested in your experience with your team. For the online Experimental Design Lab Grading Rubric for NLC CHEM Lab Reports you will reflect on a previous team experience you have had. You do not need to work in a team for the experiment. Rubric for Conclusions The table below is a guide to what is expected of a conclusion and how it will be graded. Be aware of the distinctions between “Observations” and “Results.”* ➢ Observations are descriptions of what you perceive with your senses. That is, what you see, hear, or smell (but not taste or feel since we abide by safety regulations and do not permit direct contact with chemicals in our labs!). For example if you mix two solutions and a solid forms, you can describe that you saw a solid materialize from the solutions which were previously liquid. You could write something like “a solid formed from two liquids.” The more descriptive, the better. Was there a color change? Do not merely say “it was orange” since perhaps the liquid started out an orange color. Say rather “the solution changed from green to orange.” Or “an orange solid formed from two clear liquids.” The more detailed, the better. Do NOT write the formula of the solid (even if you know it) under “Observations.” One obviously cannot “observe” the formula of a compound! (Figuring out the formula of the solid would be a “result” or “conclusion.”) ➢ Results is the presentation of the data and observations. They may be a calculation of the data or a deduction from observations. For example the result is that a precipitation reaction occurred since you observed a solid appearing in the solution. A result could be your suggestion of the formula of the precipitate. The formula of the precipitate would NEVER be an observation since we can’t see the atoms or molecules. But it could be a result that you suggest from your observations and knowledge of the solutions you mixed together. Results could also include what was learned from the experiment on an individual level and may include applications you see to the world around us. For example you could say “I had no idea that dissolving salt in water changes its physical property of freezing point! Now I understand why they “salt” the roads in icy weather.” There should be enough detail for someone not familiar with the lab to understand what was done and what was learned. The Result section should also include an error analysis. (You can put an error analysis in a separate paragraph if you prefer.) See rubric for conclusions below for details on what is included in an error analysis. The last sentence of this part should be your conclusion which is a summary of what the lab proved. *Scientific Research Journal papers also include a Discussion section. We will not deal with this since we are not doing original research. But just so you know, the Discussion section is where you analyze your results and explain their meanings. The Discussion will include any new questions (and possible answers) and perspectives and describe the most interesting points for the entire field. The Discussion section is where researchers can be wildly speculative and talk about what they think the far reaching implications are of their research. Grading Rubric for NLC CHEM Lab Reports Conclusion Part Expectation to receive full credit Explanation of Lab 4 points This is a well written sentence of the purpose or goals of the experiment. It should be the first sentence of your conclusion. For the Experimental Design lab your explanation will depend on the question/problem you are given. (Length is one sentence to one paragraph) Results and Conclusion 6 points Talk about what happened in the experiment. Did what happen support or not support your expectations? Results are not a restatement of facts and theory or a reiteration of the procedure. DO NOT include steps of the procedure in this section. The results are your interpretation of your observations and data. The last sentence of this part should be a conclusion sentence. This is a summary of what the lab proved. For our lab reports it should only be one sentence. (Length one to three paragraphs.) Error Analysis 6 points Discuss any possible errors that may have occurred in your experiment. Error analysis will first be of the technical errors that may have happened as you performed the lab. Did you notice anything wrong while performing the lab? Any spilling? Overheating? Generally when performing labs you should write down observations at each step. That way, if an unexpected result occurs you can go back and jog your memory and perhaps figure out what error caused the unexpected result. This section should be detailed and not general. Do NOT say “human error caused bad results.” Discuss the possible effects the error would have on the results. For example if the error was that “the salt solution spattered out of the beaker when drying” say that “since this error occurred I expect a lower yield of salt. Therefore my percent composition of salt in the mixture is probably lower than the actual.” You could also include how the error could be reduced. Perhaps better equipment? Or more care when boiling solutions? General statements of “human error” or “calculation mistakes” are not acceptable. (Length one paragraph.) Spelling, Punctuation and Grammar 4 points Conclusions should be free of errors in spelling, punctuation or grammar. One point deduction for each error up to 4 points. Grading Rubric for NLC CHEM Lab Reports Examples of acceptable conclusions from NLC students: These are conclusions that have the necessary elements per the rubric. Some are not particularly well written. This is a Chem class and we do not grade for literacy, only comprehensibility. Conclusion #1 The purpose of this experiment was to become more familiar with the separation of mixtures of solids. I was given a mixture of sodium chloride, benzoic acid, silicon dioxide, and iron. The mixture contained an unknown amount of each substance. I was required to separate each substance one at a time, and then find their mass and percent of the whole mixture. The experiment took a few days to complete because a few of the steps required water to evaporate, leaving behind the desired substance. Iron was the first and easiest to separate out because of its magnetic characteristics. Next, was the sand. Since sand is insoluble in water, I put the remaining mixture in water and put it over a fire. The Sand settled at the bottom of the beaker, and the remaining mixture dissolved into the water. I put the liquid mixture into an ice bath. The benzoic acid crystallized, which allowed me to filter it out, leaving behind the sodium chloride. The experiment required patience and close attention to detail. Sources of Error The errors occurred in the recovery of the mixture. I started with 5.8 grams of the mixture and finished with 5.4 grams, which is about 93%. The results were also skewed by the balance, and the fact that it only measures to a tenth of a gram. I lost part of the mixture along each step, but the major loss occurred with the sand in the beaker. I baked the sand in the oven to expedite the drying process, but some sand baked to the bottom and the sides of the container. I dislodged most of the sand, but I lost part. [Editor’s note: It would have been better to add a part about how it would be expected that this would cause the sand component results to be less.] Conclusion #2 The lab involved burning a few household items and measuring the amount of heat released so that caloric information could be calculated. By burning the food and measuring the heat released into the water, we are able to make the needed calculations. The possible errors in this lab include measuring the temperature wrong, or making the calculations incorrectly. The second error which has been discussed before in previous labs can be corrected by making sure to read the thermometer at eye level immediately after removing it from the liquid. The third error is making calculations incorrectly. This lab involved a lot of calculation which makes keeping up with Sig Figs and rounding difficult. I tried my best to reduce my errors and I thoroughly enjoyed this lab. Grading Rubric for NLC CHEM Lab Reports Conclusion #3 The purpose of this lab was to study and identify some physical and chemical properties of gases that are commonly used in the laboratory and to use these properties to identify these gases when there is a gas present. By combining certain chemicals, elements, and household products, I was able to discover the different properties that were produced and create exciting reactions. It was amazing to see the gas released by putting the water filled pipet tubes over the stoppers with plastic gas delivery tubes. The best part of the experiment was to see the immediate bubbling from adding Hydrochloric Acid to the mossy zinc and the overflow of bubbling by adding two common household items, the vinegar and the baking soda. It was also interesting to see the color change of the BTB to a yellow color indicating an acid when the gas from the reaction of the sodium bicarbonate and vinegar had taken place and been released into the BTB. Any error in this lab could have been attributed to mistakes with the pipets and releasing too much liquid or potentially mishandling and contaminating the various chemicals that I was using because there were many different combinations going on and some of them were messy. It was difficult to see a reaction with the limewater at first, but as I continued to use it, I noticed the bubbling. This lab proved very useful in becoming familiar with working with different chemicals the gas releasing or delivery equipment. It was something I had never used before and found very interesting. Conclusion #4 The objective of this lab was to identify metallic ions in solutions. I soaked cotton swabs with different salt solutions over passed them over the burner to excite the electrons of the metals in the salts. I observed and recorded the color of the flame produced by the excited electrons. I was able to notice the color for each solution that was tested. The lab experiment was very straightforward and I experienced no major complication other than the smell produced by the occasional roasted cotton swab. The only difficult color to identify was the calcium nitrate. Overall, the experiments were well planned and easy to perform. I was able to complete the lab in a minimal amount of time. I found the experiment to be interesting and enjoyed the different colors that were produced. After completing the lab, I wondered if more colors can be produced by mixing the metallic ions.
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Explanation & Answer

Please view explanation and answer below.Here you go! It went smooth. Filled the report sheet as required.

Kinetics Lab Report Sheet
Name:
Partner (if applicable):

Observations of reaction:

There were never any observable change of color as the reaction occurred. It was assumed a
reaction had occurs since, after mixing the zinc and the HCl solution, a gas evolved and it was
collected in the inverted cylinder. In addition, there was an increase in temperature in the test tube.

Data Tables:
3.0 M HCl

Online CHEM 1412 Chemical Kinetics
Trial 1
Time
30
60
90
120
150
180

mL H2

Trial 1
Time
30
60
90
120
150
180
210
240
270
300

1
10
20
38
60
70

mL H2
19
22
34
42
50
53
60
64
66
70

Trial 2
Time
30
60
90
120
150
180

mL H2
1
12
22
40
59
71

2.0 M HCl
Trial 2
Time
30
60
90
120
150
180
210
240
270
300

mL H2
20
24
34
42
48
53
60
64
66
70

Trial 3
Time
30
60
90
120
150
180

Trial 3
Time
30
60
90
120
150
180
210
240
270
300

mL H2
1
11
19
39
57
70

mL H2
19
23
35
39
47
54
58
65
67
70

1.5 M HCl
Trial 1
Time
Dallas College

mL H2

Trial 2...


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