Student Name: Justin Stoichiometry Lab SUBMISSION DOCUMENT Assessed Criteria: D (Scientific Inquiry), E (Processing Data), F (Attitudes in Science), B (Communication) Aim: investigate one factor affecting the change in yield of a chemical reaction Instructions Submit work on this document, self-­‐assessed. Use APA citations in-­‐text and references. Include at least 3 reliable external sources. Learn from your previous labs: be organized and self-­‐assess as you go. Write clearly. Follow the guidance. Delete all red guidance text before submission. •
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Academic honesty declaration: “I confirm that this work is my own work and is the final version. I have acknowledged each use of the words or ideas of another person, whether written, oral or visual. Although I have worked with a partner on collecting data, all written work and data processing is my own.” Signed: Justin
Type your name on the line above when the work is complete. Date: 1/27/2013 Criterion D: Scientific Inquiry Self-­‐assess by highlighting statements that best describe your work Level Descriptor 0 1-­‐2 3-­‐4 5-­‐6 The student does not reach a standard described by any of the descriptors below. The student attempts to state a focused problem or research question. The method suggested is incomplete. The student attempts to evaluate the method and respond to the focused problem or research question. The student states a focused problem or research question and makes a hypothesis but does not explain it using scientific reasoning. The student selects appropriate materials and equipment and writes a mostly complete method, mentioning some of the variables involved and how to manipulate them. The student partially evaluates the method. The student comments on the validity of the hypothesis based on the outcome of the investigation. The student suggests some improvements to the method or makes suggestions for further inquiry when relevant. The student states a clear focused problem or research question, formulates a testable hypothesis and explains the hypothesis using scientific reasoning. The student selects appropriate materials and equipment and writes a clear, logical method, mentioning all of the relevant variables involved and how to control and manipulate them, and describing how the data will be collected and processed. The student evaluates the method, commenting on its reliability and validity. The student comments on the validity of the hypothesis based on the outcome of the investigation. The student suggests realistic improvements to the method and makes suggestions for further inquiry when relevant. Page 1 Student Name: Justin Criterion E: Processing Data Self-­‐assess by highlighting statements that best describe your work Level Descriptor 0 1-­‐2 3-­‐4 5-­‐6 The student does not reach a standard described by any of the descriptors below. The student collects some data and attempts to record it in a suitable format. The student organizes and presents data using simple numerical or visual forms. The student attempts to identify a trend, pattern or relationship in the data. The student attempts to draw a conclusion but this is not consistent with the interpretation of the data. The student collects sufficient relevant data and records it in a suitable format. The student organizes, transforms and presents data in numerical and/or visual forms, with a few errors or omissions. The student states a trend, pattern or relationship shown in the data. The student draws a conclusion consistent with the interpretation of the data. The student collects sufficient relevant data and records it in a suitable format. The student organizes, transforms and presents data in numerical and/or visual forms logically and correctly. The student describes a trend, pattern or relationship in the data and comments on the reliability of the data. The student draws a clear conclusion based on the correct interpretation of the data and explains it using scientific reasoning. Criterion B: Communication in Science Self-­‐assess by highlighting statements that best describe your work Level Level descriptor 0 The student does not reach a standard described by any of the descriptors below. 1–2 The student uses a limited range of scientific language correctly. The student communicates scientific information with limited effectiveness. When appropriate to the task, the student makes little attempt to document sources of information. 3–4 The student uses some scientific language correctly. The student communicates scientific information with some effectiveness. When appropriate to the task, the student partially documents sources of information. 5–6 The student uses sufficient scientific language correctly. The student communicates scientific information effectively. When appropriate to the task, the student fully documents sources of information correctly. •
Use at least three reliable eternal sources, cited in-­‐text and references, using APA. See the resources here for guidance on using APA in the Word Citation Tool: https://sites.google.com/a/canacad.ac.jp/academic-­‐honesty/apa-­‐method Criterion F: Attitudes in Science Self-­‐assess by highlighting statements that best describe your work Level Descriptor The student does not reach a standard described by any of the descriptors below. 0 1-­‐2 3-­‐4 5-­‐6 The student requires some guidance to work safely and some assistance when using material and equipment. The student requires some guidance to work responsibly with regards to the living and non-­‐living environment. When working as part of a group, the student needs frequent reminders to cooperate with others. The student requires little guidance to work safely and little assistance when using material and equipment. The student works responsibly with regards to the living and non-­‐living environment. When working as part of a group the student cooperates with others on most occasions. The student requires no guidance to work safely and uses material and equipment competently. The student works responsibly with regards to the living and non-­‐living environment. When working as part of a group, the student cooperates with others. Page 2 Student Name: Justin Research Question: “How does changing the mass of sodium bicarbonate affect the yield of sodium chloride ” Background Balanced equation: HCl(aq) + NaHCO3 (s) NaCl (aq) + CO2(g) + H2O(l) Type of reaction, with reason: •
Neutralization: this is a neutralization reaction because in a neutralization reaction, salt is always produced. Alongside this, there can also be water. As you can see in the reaction equation above, NaCl (salt) has been produced and so has H2O (water) (Ophardt, 2003). Define yield. What are some variables you could change in order to affect yield in this reaction? •
How many elements gets produced or extracted from the reaction. In this case, the mass of sodium bicarbonate can affect the yield of sodium chloride (McClinton, McClinton, & Douglass, n.d.). Molar Masses: HCl 36.46g/mol NaHCO3 84.01g/mol NaCl CO2 H2O 58.44g/mol 44.01g/mol 18.02g/mol Variables Independent: Measured by: Reason for choosing this: Dependent: Measured by: Hypothesis Mass of sodium bicarbonate Units & uncertainties grams (± 0.01) Using an electronic mass scale I chose this because I know that by changing the mass of products, then the mass of the yield also has to change. I chose to use the electronic mass scale in this situation because it is the most accurate scale available to me in the lab. Mass of salt Units & uncertainties grams (± 0.01) Weighing the beaker with salt in and after the beaker is washed clean. Predict the effect of your independent variable on the dependent variable •
My hypothesis for this experiment is that as I increase the amount of sodium bicarbonate that I put in, I will have a higher yield of sodium chloride. Also, looking at the stoichiometric relationship, we know that for every one mole of NaHCO3, we get one mole of NaCl. This is why I know that as I increase the amount of sodium bicarbonate I put in, I will get a steady increase of salt as well. •
Stoichiometry example: HCL + NaHCO3 -­‐-­‐-­‐-­‐-­‐ NaCl + CO2 + H2O 2(HCL) + 2(NaHCO3) -­‐-­‐-­‐-­‐ 2(NaCl) + 2(CO2) + 2(H2O) Page 3 Student Name: Justin Give a sketch graph of your predictions Graph 1: predicted data 3.000 Product yield 2.500 2.000 1.500 1.000 0.500 0.000 0.000 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000 3.250 3.500 3.750 4.000 4.250 Increments Table 1: predicted data Reactant: NaHCO3 Product: NaCl Molar Mass: Increment (g) Moles 0.000 0.000 Molar mass: Predicted yield product (mol) Predicted yield product (g) 0.000 0.000 84.01 g/mol 0.500 0.006 1.000 0.012 2.000 0.024 58.440 g/mol 0.006 0.351 0.012 0.701 0.024 1.403 4.000 0.048 0.048 2.805 In terms of how I got these predictions, it’s very simple. First, the increments that I used are in that way because it is easier to work with. Since to get to the next increment, you have to multiply by two, and the moles would also be easy to predict just using those increments. Next, in order to get the moles, all you have to do is divide the increment by 84.01. We have to do this because the increment is how much of sodium bicarbonate we are putting in, so we need to find how many moles that is. We know that one mole of sodium bicarbonate is 84.01, so the answer should be below 1. Calculations: 
0.500/84.01= 0.0059 
1.000/84.01= 0.0119 
2.000/84.01= 0.0238 
4.000/84.01= 0.0476 Next, we had to find out the yield of salt in moles, but since we know the stoichiometric relationship between sodium bicarbonate and salt, this is easy. The ratio is 1:1, so the product of salt in moles is the number of moles of sodium bicarbonate reacting. And then, using those numbers, we multiply them by the molar mass of salt, which is 58.440. Calculations: 
𝟓𝟖. 𝟒𝟒𝟎×𝟎. 𝟎𝟎𝟔 = 𝟎. 𝟑𝟓𝟎𝟔 
𝟓𝟖. 𝟒𝟒𝟎×𝟎. 𝟎𝟏𝟐 = 𝟎. 𝟕𝟎𝟏𝟐 
𝟓𝟖. 𝟒𝟒𝟎×𝟎. 𝟎𝟐𝟒 = 𝟏. 𝟒𝟎𝟐𝟓 Page 4 Student Name: Justin 
𝟓𝟖. 𝟒𝟒𝟎×𝟎. 𝟎𝟒𝟖 = 𝟐. 𝟖𝟎𝟓𝟏 Predict the maximum change in your DV for each mass of solid you use. •
When I use 0 grams of sodium bicarbonate, I obviously will get 0 grams of salt, because I didn’t put anything in. •
When I put in 0.006 moles of sodium bicarbonate, I should be getting no more than 0.351 grams of salt. We know this because if NaHCO3 is 0.006 moles, then so is NaCl. This is the same for all, so I can look at the table above to complete this part. •
When I put in 0.012 moles of sodium bicarbonate, and if all of it is reacted, then I should be getting no more than 0.701 grams of salt. •
When I put in 0.024 moles of sodium bicarbonate, and if it is fully reacted, than I should be getting no more than 1.403 grams of salt. •
With 0.048 moles of sodium bicarbonate, and if we are to assume that all of it reacted, than we should be getting no more than 2.805 grams of salt. Explain your predictions To begin with the explanations, we can look at the stoichiometric equation. For the experiment that I did, the stoichiometric equation is as follows: HCl + NaHCO3  NaCl + CO2 + H2O. I used this as my main way of coming up with my hypothesis. As stated above, my hypothesis is that as I put in more sodium bicarbonate, the mass of salt will increase as well (at a constant rate). Since the molar ration is 1:1 between those two, the increase in sodium bicarbonate should be steadily increasing with the mass of salt produced. The whole equation sets up fundamental knowledge for people who need to predict the outcome of things. Using the equation above, we know that for every mole of HCl, you need one mole of HaHCO3, we produce one mole of NaCl, one mole of CO2, and one mole of H2O (Yield, n.d.). Using these numbers, we know the ratio 1:1  1:1:1 (Stoichiometric ratios, 2005). That’s why in my hypothesis, I was able to predict that the amount of salt will constantly increase as you put in more sodium bicarbonate. Page 5 Student Name: Justin Experimental Design Controlled Variables Identify Variables Concentration of HCl Same beakers possible) (cleanest Filter paper Mass of sodium bicarbonate Same balance Possible impact on results If we don’t keep the same amount of HCl, then it can possibly affect our results at the end. Since we are determining the pattern of how salt increases when you add more of sodium bicarbonate, if we change the concentration of HCl, then the experiment becomes different. In order to get accurate results, we need to keep the same concentration of HCl. If you don’t use the same beaker each time, than your results can be varied. For example, the beaker can be dirty, and that can as change the weight of the beaker. Or, if you accidentally mix up two different masses of sodium bicarbonate, it will also mess up the end results with the mass of salt. Using different filter paper can possibly affect the mass of salt at the end. If there is something inside of the filter paper and you don’t see it, it might get into the salt and alter the mass. That’s why it’s important to use fresh new ones for each beaker. Putting in more or less than what we are supposed to put in will affect our end conclusions. For example, I predicted that when 0.5 grams of sodium bicarbonate is reacted with HCl, 0.351 grams of salt would be produced. Now, if I accidentally put in 0.7 grams of sodium bicarbonate, my predictions are no longer valid, and the experiment will have to be changed a little. If the balance is sort of weird or not functioning properly, it can change the results that we collect later on. That’s why I always use the same balance to weigh everything Specific method for control In order to control this variable, all we had to do was take a beaker and measure out each time, how much HCl we were going to use. For this experiment, we used 30 milliliters of HCl. In order to control this variable, all we had to do was label our beakers. We just took scrap pieces of paper and wrote down the increments and taped it to the beakers so we didn’t get confused. Also, I checked each individual beaker to make sure that they were the same. In order to accomplish this, all we had to do was get them all from the filter paper pile. They were all new ones too. In order to control how much sodium bicarbonate was entering each beaker, I used the electronic scales that were available in the class. I put the plastic container on the balance, zeroed it, and put the powder in until I got what I wanted. All I have to do is make sure to use the same balance. If it means labeling it, than so be it. Page 6 Student Name: Justin Uncontrollable variables Identify Variables Evaporation of HCl Possible impact on results This is uncontrolled because we do not know if all of the liquid was evaporated or not. All though we used an oven to evaporate it over night, there is a possibility that all of it hadn’t evaporated. In this case, it will affect our end results when we measure the mass of salt. Instead of getting what we should be getting, we will add the mass of that left over liquid, and it will alter our experiment. We will not be able to get reliable results. Materials & Equipment 1. Safety goggles to protect eyes 2. Eight medium-­‐sized beakers (that can contain more than 100 ml) (Milliliters ± 0.1) 3. HCl (Total of 120 ml) 4. Beaker for HCl (more than 100ml) (Milliliters ± 0.1) 5. Sodium bicarbonate (Total of 7.5 grams) 6. Electronic scale (Grams ± 0.1) 7. Filter (Four) 8. Filter paper (Four) 9. Oven for evaporating, or natural is ok (but takes much more time) Method for manipulating the independent variable For this experiment, I used the increments 0, 0.5, 1.0, 2.0, and 4.0. Now technically, I only have four because if you put in 0 grams of sodium bicarbonate, than you can’t produce any salt. But, we can count that as an increment because it still helps us determine how much it has increased from 0 to 0.5. I decided to go with this because I thought that for our sake, if we went up by two times the last one, than the pattern would be clearer, as it follows sequence. For instance, if I used 1.0, 3.0, 5,0, and 9.0, it would be harder to determine the relationship and pattern. But if everything goes up by two, than the pattern would be easier to see. In order to get these increments ready, I used the electronic scale and weighed out each of the increments of sodium bicarbonate. Method for recording the dependent variable The following are the steps we took in order to get to the part where we recorded our dependent variable: 1. Pour 30 ml of HCl into each of the four beakers. The numbers on the beaker was used to measure out 30 ml. 2. Put in the different increments of sodium bicarbonate in its corresponding beaker. It doesn’t which beaker gets which one, as long as you put one increment of sodium bicarbonate in one beaker. 3. Wait until the reaction stops. This part might take a couple minutes, so allow it to do what it has to do. 4. Next, use the other four beakers to set up the other part of the experiment. Line up the beakers, take the filter and filter paper, and lay them in the empty beakers so that you are ready to pour the HCl and sodium bicarbonate into the empty ones. 5. Pour the HCl into the empty ones and leave them until there is no liquid left in the filter paper. This will also take a couple minutes. 6. After all the liquid has gone and there is no more left in the filter, take it out and throw it away. Then take the newly filled beakers that have been filtered and evaporate the liquid that’s inside. You can do this anyway you want, but a heating oven is the quickest way to do this. 7. After the evaporation has finished, you are ready to record your data. First, measure it with the salt inside. 8. Wash each beaker thoroughly after measuring the beaker with the salt, and then weigh again. Just subtract the weight of the beaker that’s been cleaned and the beaker that had salt and that is the weight of your salt. Measurements: Page 7 Student Name: Justin Throughout this process, we had to measure how much of something we were putting in. First, we had to measure how much HCl we were putting in into the beakers. Than, we had to measure how many grams of sodium bicarbonate we were putting into those beakers. And then at the end, we had to measure the weight of the beaker with salt in it, and the beaker itself after it has been thoroughly cleaned. Calculations: The only calculation we did throughout this experiment was at the end, when we had to subtract the two numbers. In order to find the mass of salt that was produced, we had to subtract the beaker that was clean from the beaker with salt in it. For example, if we had a beaker with salt that weighed 150 grams, and the same beaker but washed and it weighed 135 grams, than that would mean that the salt weighed 15 grams. (Assuming that the beaker was washed cleanly). Method for collecting sufficient relevant data For each increment that we had, we had to do a repeat of three times, just to be sure. This got started in my head because when I weighed the one with 1.0 gram of sodium bicarbonate, the first result was lets say 115.0, but when I accidentally measure it again, it was 109.0. This is why I did everything again and realized that I should measure everything three times just to be safe. The silly thing was that I only did this for the second half. When I was measuring the beaker when it had the salt in it, I measured each one once only. But when I measured the cleaned beaker, I measured each one three times. If I could redo the experiment, I would definitely go back and measure the beaker with salt in it three times as well. This would reassure me that the results are quite reliable. Photo or diagram: Figure #1: This is HCl. This is the liquid that we used for our experiment (HCL, n.d.). Figure #2: This powder you see here is HaHCO3, the sodium bicarbonate that we used in this experiment (Sodium bicarbonate, n.d.). Page 8 Student Name: Justin Figure #3: This is a beaker. This is the kind of equipment we used to measure out and contain the sodium bicarbonate and HCl (Graduated beakers, n.d.). Safety: For this experiment, in order to be safe to yourself, you first have to put on goggles so that if anything splashes out, it doesn’t go into your eyes. In order to be safe to the environment, just don’t fool around. Make sure you don’t knock the beakers with HCl down, and do not put laptops near the experiment area. Page 9 Student Name: Justin Data Collection & Processing Qualitative Data (observations) •
While we were doing the experiment, I was able to observe one thing. Every time I put the sodium bicarbonate into the concentration of HCl, the whole beaker would turn white, and everything will start fizzing. This was quite obvious, as this started the second a dropped the sodium bicarbonate into the beakers. Than, after an estimated time of 15 seconds, the fizzing stopped, and all actions stopped. Raw Data Increments
0.500
1.000
2.000
4.000
Predicted
0.351
0.701
1.403
2.805
Actual
0.300
0.670
0.910
2.700
Data Processing In order to use the data that I have retrieved, I need to use the application called Excel. Excel is the brother of the Microsoft applications that allows you to make tables, and it is the easiest tool to use for making tables and graphs. First, you have to set up the table with headings, like the raw data above, but you also need units and uncertainties. You also need a descriptive title so that you know what the table is about, and if there are others, then which one of those it is. For graphs, we need to have axis labels that clearly describe what they are representing, and they also need units and uncertainties. The graph also needs a descriptive title, so you know which one you’re working with. In some cases, if you have more than one line, which is in my case, then you have to label those lines to show what they are representing. This is how we can turn raw data into process data in the form of tables and graphs. Calculations: 1.
Finding moles of NaHCO3 (One mole is 84.01): As an example of a calculation, if you had an increment of 3.0, then you would divide 3.0 by 84.01 to find the moles. 3.0/84.01 ≈ 0.036 moles 2.
Converting moles to grams for the product (1 mole of NaCl= 58.440): Since we know that NaHCO3 is 0.036 moles, we know that NaCl is 0.036 moles. Now, we just convert that into grams. 58.440×0.036 ≈ 2.104 𝑔𝑟𝑎𝑚𝑠 This is how I predicted the yield of salt in grams. 3.
The actual experiment, Finding the actual mass of salt: First, we measured the beaker with salt, and then after you clean it, you weigh it again, and the difference gives you the mass of salt. For instance, lets say that the beaker with salt was 160 grams, but the washed beaker was 142 grams, we know that the salt was 18 grams. 160 − 142 = 18 4.
Finding the error and percentage error Now lets take that 18 grams, and compare it with 25 grams. Let’s just say that the actual was supposed to be 25, but I measured 18. To find the error, we have to subtract 25 from 18. 18 − 25 = −7 (Ignore the negative signs in this case) The error is 7. To find the percentage error, you divide the error by the actual. So in this case, we divide 7 by 25. 7
= 0.28, 28% 25
The percentage error is 28%. In order to process my data in the format of a table on excel, I didn’t need any special function. All you have to do is make your table with the headers and labels and all, and then put in your information. With the graph, it’s a bit more complicated. First, you have to highlight the numbers that you want to use for the graph, and then go to tool bar Page 10 Student Name: Justin and click on the tab that says graph. When you click on it, you are given different forms of representation, so choose one. After you have made the graph, you can replace axis by going to the tool bar at the top and selecting “graph layout”. There, you can choose to add titles axis, and many other functions. That’s all you need to know for the graph in order to process your data. Comparison of expected and predicted yield of salt: Increment of 0.5 0.300 − 0.351 = −0.051 0.051
≈ 0.15 0.351
= 15% Increment of 1.0 0.670 − 0.701 = −0.031 0.031
≈ 0.04 0.701
= 4% Increment of 2.0 0.910 − 1.403 = −0.493 0.493
≈ 0.35 1.403
= 35% Increment of 4.0 2.700 − 2.805 = −0.105 0.105
≈ 0.04 2.805
= 4% Judging by the percentage error of the increments, I can see that one seemed way off. It is over a quarter of a 100 percent below the expected mass. This means that something must’ve gone wrong while I was doing the experiment. Everything else is not terribly off, and I can see that the increments of 1.0 and 4.0 were quite close. Processed Data The mass of the yield of salt that was predicted and that was measured Increments of the IV (g)(±0.01 )
0.00
0.500
1.000
2.000
4.000
Predicted Yield (g) (±0.01 )
0.000
0.351
0.701
1.403
2.805
Measured Yield (g) (±0.01 )
0.000
0.300
0.670
0.910
2.700
Graphical Representation Page 11 Student Name: Justin 3.000 2.500 2.000 Yield of salt (g) (± 0.01) Graph 2: The yield of salt predicted vs. The yield of salt that was measured 1.500 1.000 0.500 0.000 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60 2.80 3.00 3.20 3.40 3.60 3.80 4.00 4.20 -­‐0.500 Increments of sodium bicarbonate (g) (± 0.01) Predicted Yield Measured Yield Page 12 Student Name: Justin Analysis of Data Description of trends, patterns and relationships Looking at my processed data, there is one outlier. If that outlier weren’t there, than the trend line would look linear. For some reason, all the numbers but the one for the increment 3.0 was very off. In terms of relationship, you can see that both points are close to each other, showing us that they are increasing at the same rate, except for the increment of 3.0. So this means that as the increment of the sodium bicarbonate increases by two, so does the mass of the predicted yield of salt. This is all true for the measured results as well, except that one outlier makes the end conclusion a bit more difficult. The same patterns also appear on the table, which has the exact same numerical data as the processed graph. We can say from this processed data, that in general, as the x values double, so do the y values. Reliability of the data In general, the data that I gathered was reliable. Except, that’s what I thought until I saw the outlier in the processed graph. Everything else seems reliable because I repeated the measurements three times to be sure, and I did that with the outlier as well, and so I don’t know why I got a number that was way off from the prediction. If I did this experiment again, I would get the same results for the increments of 0.5, 1.0, and 4.0, but I believe that if I did the experiment for the increment of 3.0 again, I would get a different result. I can say that only half of my data is very precise. This is because when I measured the beaker with the salt inside, I only measured it once, so I could’ve made a mistake or forgotten to zero out the numbers, or anything technical like that. But, luckily for me, I remembered to repeat the measurements when I measured the beaker after it had been washed. I took three measurements for each increment with the beaker that was washed cleanly. I am quite confident of the results I received for all but the one with the increment of 3.0. I personally cannot believe the results I got for the increment of 3.0 are true. In the data, the uncertainty is quite small. Since I used an electronic balance, the uncertainty on that was ± 0.01. That is a very low uncertainty, so it should be quite accurate in the readings. And this is why when I consider the fact that the uncertainty is ± 0.01, I start to feel like the results for the increment of 3.0 might actually be correct, but it’s not good enough to convince me. But, if I was to make a conclusion, I would be able to use my results because 75% of it I am very sure is correct, so overall, I am quite confident about my results. Evaluation of the hypothesis Judging by the data that I received from the experiments, my hypothesis was very valid. As my hypothesis, I said that as the increments of sodium bicarbonate increases, the salt produced at the end will also increase. And since the stoichiometric ratio is 1:1 between those two compounds, and so the rate at which they increase should remain constant. First, in order to prove that the first part of my hypothesis is correct, we should take a look at the processed table of the data. First of all, as you can see, as the increments increased, the yield of salt also increased. This was a very obvious hypothesis because if you increase the amount of sodium bicarbonate, you are increasing the mass of it, hence you are adding more reactants, and therefore, more products are produced. That is why as I increased the mass of sodium bicarbonate that I put in, I yielded more salt. Next, the second part of my hypothesis was about the fact that the rate at which they increase will be constant, and they should be similar. So that means that if the increments/moles of sodium bicarbonate double, than the yielded salt should also double. Now let’s take a look at the table. As far as things go, the results are being doubled, but that outlier makes it harder to evaluate the hypothesis. From 0.300 to 0.670 is pretty much doubled, but since the third one is 0.910, the pattern or trend is broken. If it was around 1.3, which is what it should be ideally, then the pattern would be constant throughout. I believe that there was some calculation error a moment of electronic balance failure/malfunction. If I were to get rid of the outlier and add in the ideal result, than I could say that my hypothesis is valid. So in conclusion, I can say that my results show that my hypothesis is quite valid. If I could do something about the outlier, than my hypothesis would be completely valid without a second thought. Page 13 Student Name: Justin Conclusion By looking at the data that I got, first, I already stated that my hypothesis was valid. Also, they show me that the stoichiometric formula and ratios work and are also valid. Using the stoichiometric formula, I was able to predict the yield of salt for each increment I chose. Since my question was, “How does changing the mass of sodium bicarbonate affect the yield of salt,” the results that I got were completely appropriate. These results answer my research question, while also validating my hypothesis. Now, we can talk about how my results can be compared to the predicted numbers. For an example, let’s take a look at the increment of 1.0. For that increment, using the stoichiometric formula, I was able to predict that 0.701 grams of salt was going to be yielded, but in reality, I yielded 0.670 grams of salt. Now, to be honest, that is very close, and the percentage error is actually 4%. This means that my results were not accurate, but were very close to being accurate. There could’ve been a couple factors that affected the mass of salt, or seemed to make us think that the salt was what it was. For instance, during the experiment, we could’ve spilled some of the HCl during the transportation step. If any HCl splashed out, than it carried elements with it, and so by all means, the HCl that we supposedly spilled could’ve carried 0.031 grams of salt with it. This is the likeliest way we could’ve lost salt in the experiment. This went the same for all our results. All of them, except for the one for the increment of 3.0, were slightly below the predicted yield. On the other hand though, the measured results seem to be reliable, as the stoichiometric equation told us that the rate of increase was to be constant. From 0.300 to 0.670 is approximately times two, but from 0.670 to 0.910 is not multiplied by two. If, on the other hand, the increment for 3.0 was more realistic, like 1.3, than the trend would’ve continued throughout, because the number after is 2.7, which is also approximately two times the ideal measurement for the increment of 3.0. What scientists refer to what I am talking about is called theoretical yield. This basically talks about the products that will be yielded if the experiment were to react completely (Theoretical yield, 2013). Using this, we can tell that the results we got were not wrong, but have been altered because of the method that we used. Before, I also mentioned how we could’ve lost some products while doing filtration, but there are other ways we could’ve gotten the outlier. There is always the fact that the reaction wasn’t fully reacted, in which case, there’s no way you will get 100% of your reaction. Also, there could’ve been miscalculations, which is likely (Percent yield, theoretical, 2011). This is very likely because miscalculations in measurement can usually be caused by malfunctions in calculators, or just the fact that you made a mistake. I calculated the numbers on paper, so if I carried the one to the wrong place, than it definitely would’ve given me a different result. These are the possible reasons for why my results were what they were, being lower than the predicted yield. The aim of my research question in this was to help me lead the experiment, and the point of the experiment was to change the mass of sodium bicarbonate I put into different beakers to see what the different in yield would be. I would say that I have met the aim of my research question nearly to the fullest. Since I used different increments to measure different yields of salt, my research question’s aim was fulfilled to pretty much its fullest. Page 14 Student Name: Justin Evaluations Validity of the method The method we used to conduct this experiment was very valid. First, we asked Mr. Taylor for guidance, and he suggested we do this, and second, it was the most logical thing to do, as we were trying to find the mass of salt produced depending on how much sodium bicarbonate we put in to the HCl solution. First, we pour HCl into a beaker and we put in the sodium bicarbonate, this first step is valid. Then, after the reaction has stopped, we pour the liquid into another beaker, through filter paper. This step is also valid because the filter paper gets rid of any solids that may be in the way of the experiment and our success. Than, we put the beaker into an oven and evaporate the HCl until only salt is left in the beaker. This is also valid because we already know that to separate what’s in the liquid from the liquid itself, you have to evaporate the liquid. After that is done, all we had to do was measure the beaker with the salt inside, and then clean it, and then weigh it again. This step is also valid because we need to find what’s inside the beaker, which is the salt. If we measure the beaker with the salt, and than measure the beaker when it’s completely clean, than we know the mass of whatever was inside (which is salt in this case). This is why the method used to obtain the mass of salt and everything else is valid. Reliability of the method Overall, the method was reliable, but there was one step that we took that might be not as reliable. For instance, when we transport the HCl solution to the other beaker through the filter paper, there could’ve been some mishaps. For instance, if we didn’t recognize it, there could’ve been a hole in the paper, and it would’ve added more mass to the end result. That was one part that was not reliable, but I believe we had no other way of separating the solids from the liquids as easily. Than came the washing of the beaker. This step is also not reliable, because the results that we get will depend on how clean we washed the beakers. If we were lazy and didn’t wash the beakers properly, than it could’ve added more mass to the end result. These two were the only steps that we took that weren’t that reliable. Basically, depending on how careful we were, the results could’ve been altered. Evaluation of specific limitations and sources of error Source of error/ limitation Concentration of HCl Same beakers Sodium bicarbonate powder Filter paper Potential impact on results, with magnitude (1-­‐10 (Affected a lot)) Can affect the yield of salt, but the problem is most likely not a big deal. (4) Outline a specific method to improve this error/ limitation In order to improve this, we can take a beaker with the most specific marks, so that it is easier to be accurate. The more marks there are, the easier it becomes to pour out the right amount of HCl. If you use different beakers, than the Simply put, in order to make sure you use results can be different. If one beaker is the right beakers, all you have to do is label dirtier than the one you used, it could them. Since you will be using similar add more mass. This could be potentially beakers (assumable), you should label a big deal. (7) them so you don’t get confused. Adding in the wrong amount of sodium This has to do with the limitation of the bicarbonate as described is not a electronic scale, and that’s because the scale we used only measures to the closes 0.01, so it’s not as accurate as we want it to be. The best we can do is to double check that the weight of the bicarbonate powder is correct. Although it might be harmful to the In order to solve this source of error, all environment to not reuse paper, but in you need to do is make sure that you pull an experiment like this, it is important to out filter paper from the original packet get fresh new ones, because that was, you that it came in. will be able to get more reliable data. If you get one from some where and it was lying around, you never know what had happened to it, but if it’s fresh from the Page 15 Student Name: Justin packet where it came from, it should state how much each piece weighs. This is a big problem if you make a mistake and use a dirty one. (7) Washing beakers Electronic balance This is a slight limitation to our experiment. The results that we got depended on how clean we were able to wash the beakers. If we washed it and scrubbed it clean, than our results would’ve been reliable, but if we took the short way and only rinsed and cleaned, than it could’ve added more mass than what it should’ve gotten. If this were the case, than it would a big deal. (8) This is a source of limitation because it can only do as much as weigh things. Even if it was off, or not correct, we wouldn’t know that, and when we did find out, it would be too late. If we rely on the technology too much, than one day, it will really let you down. This is a small issue, as there are many solutions to this limitation. (3) To limit this limitation, you need to make sure that you scrub as well, not just rinsing. If it is hard to wash, like a tapering beaker, than the best you can do is get a toothbrush (that won’t be used) and scrub as much as you can. For the balance issue, all you can do is to unplug and plug in again, if it is acting up. And, if you want to be sure about you’re results, than you can weigh it once, turn it on then off, and weigh it again, and see if it’s precise. Suggestions for further inquiry By doing this investigation, I think that a future one can be about the difference in concentration of HCl. Throughout the experiment, I’ve been wondering whether or not the different concentrations of HCl would affect the experiment, and so that’s why I had to be very careful with how much I put in. So for the next investigation, I would like to determine whether or not different concentrations of HCl make a difference. So each beaker will have 5 grams of sodium bicarbonate, and I will pour different concentrations of HCl into each one and see if I get different results. Page 16 Student Name: Justin References Graduated beakers [Photograph]. (n.d.). Retrieved from
http://www.rickly.com/sai/images/GRADBEAK.JPG HCL [Photograph]. (n.d.). Retrieved from http://www.mentorfitnesscoach.com/wpcontent/uploads/2012/08/Bottle-HClNaOH.jpg McClinton, M., Dr, McClinton, D., & Douglass, M., Dr. (n.d.). Product yields in chemical reactions.
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http://www.elmhurst.edu/~chm/vchembook/183neutral.html Percent yield, theoretical yield, and actual yield. (2011). Retrieved January 26, 2013, from
http://www.sglearnonline.com/percent-yield.html Sodium bicarbonate [Photograph]. (n.d.). Retrieved from
http://www.ugolice.co.nz/shop/images/bakingsoda.jpg Stoichiometric ratios. (2005). Retrieved January 25, 2013, from
http://www.chembuddy.com/?left=balancing-stoichiometry&right=ratio-proportions Theoretical yield. (2013). Retrieved January 24, 2013, from
http://orgchem.colorado.edu/Technique/Procedures/Notebook/Yield.html Yield. (n.d.). Retrieved January 22, 2013, from http://www.ausetute.com.au/yield.html Page 17