Decomposition of Hydrogen Peroxide

Transcription

1 SCIENCE - UNIT 4 - CHEMISTRY, BOON OR BANE? Decomposition of Hydrogen Peroxide Investigation of a Factor Affecting the Rate of a Reaction Prepared for: Ms. Homanchuk 25 February, 2014 Prepared by: William Hu

2 SCIENCE - UNIT 4 - CHEMISTRY, BOON OR BANE? PURPOSE To observe how a factor could affect the reaction rate. To learn how to produce a graph of reaction rates. To learn how to find the average rate of reaction. RESEARCH QUESTION How does the amount of catalyst affect the reaction (mass over time taken) of the decomposition of hydrogen peroxide? HYPOTHESIS If a higher amount of catalyst is mixed with hydrogen peroxide, then the average rate of reaction (measured using mass change over time taken) will increase as well, because the catalyst is a compound that creates more collisions between particles, resulting with an acceleration in the reaction (The Effect of Catalysts).

3 SCIENCE - UNIT 4 - CHEMISTRY, BOON OR BANE? VARIABLES Independent Variable: Amount of Catalyst (mg) Independent Variable What is the Range? How will it be Prepared? Amount of Catalyst (MnO From 50mg to 250mg It will be measured by the following procedure: 1) Place the weight boat onto the digital balance, along with pressing the tare button. 2) Pour the catalyst powder into the weight boat. 3) Measure the weight of the catalyst and make sure it s following the variable s range. Dependent Variable: Average Rate of the Reaction using Mass Change over Time Taken Dependent Variable How will it be Measured? Average Reaction Rate (Mass Change Time) It will be measured by the following procedure: 1) Find the mass change with a balance after the reaction stopped. 2) Record the time it takes for the reaction to stop, by using a timer. 3) Divide the mass change by the time taken to measure the reaction. 4) After 3 trials, find the average reaction rate. Controlled Variables: Temperature, Concentration and Amount of Hydrogen Peroxide Controlled Variable Temperature Concentration of Hydrogen Peroxide (H Amount of Hydrogen Peroxide (H How will it be Monitored? The experiment will be completed under the same environment (same room), so that the temperature is constantly the same. I will make sure that all of the hydrogen peroxide solution shares the same concentration of 5%. I will make sure that the amount of hydrogen peroxide solution are all in 25 ml. Equipment Use - Beaker I will make sure that I m using the same beaker constantly, since the beaker has its own unique mass.

4 SCIENCE - UNIT 4 - CHEMISTRY, BOON OR BANE? MATERIALS 1 x 100mL Beaker 1 x Digital Balance Scale 1 x Stop Watch 1 x Weight boat 1 x Spatula 375 ml of 5% Hydrogen Peroxide (H2O2) 2,250 mg of Catalyst (MnO2) 1 x Lap Top METHOD Starting the Lab 1. Wear safety goggles and lab coat. 2. Gather all of the materials needed. 3. Create qualitative and quantitative tables to record any data or observations. 4. Place the 100mL beaker and the digital balance scale onto a table. 5. Plug in the digital balance with an electricity source. 6. Find the weight of a weight boat. 7. Find the weight of the 100mL beaker. Data Collection 8. Pour 25mL of Hydrogen Peroxide into the beaker. 9. Place a weight boat onto the digital balance. 10. Press the tare button on the digital balance. 11. Using a spatula, pour the Catalyst powder onto the weight boat until the balance says it s 50mg. 12. Place the beaker of Hydrogen Peroxide onto the digital balance.

5 13. Pour the 50mg Catalyst powder into the beaker. 14. At the same time, start the timer. 15. Within every 15 seconds, note down the current time and mass onto the lap top. 16. When the mass remains constant (reaction stopped), stop the timer. 17. Repeat step step 7-15 for two more trials. 18. Repeat step 7-15 for three trials, but change 50mg of Catalyst to 100mg. 19. Repeat step 7-15 for three trials, but change 50mg of Catalyst to 150mg. 20. Repeat step 7-15 for three trials, but change 50mg of Catalyst to 200mg. 21. Repeat step 7-15 for three trials, but change 50mg of Catalyst to 250mg. Ending the Lab 22. Clean up everything used in this lab. (Criterion F) Data Processing 23. Duplicate all of the data into Excel. 24. Decide the uncertainty for each range. 25. Calculate the average reaction rate for each trial. 26. Calculate the average reaction for each increment (using the averages from the 3 trials). 27. Calculate the upper and lower ranges. 28. Make a graph of reaction rates for the 5 ranges. 29. Explain any patterns or trends noticed in the data analysis section.

6 DATA COLLECTION Table #1: Raw Data Table of the Reaction of 50.00mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Time ±1 (s) Mass Trial #1 ± 0.10 (g) Mass Trial #2 ± 0.10 (g) Mass Trial #3 ± 0.10 (g) * Due to the space constraint, the data shown above is the not the full data, it has been condensed (to every 30s). In addition, although this cannot be seen from the table above, all of the data has reached a plateau. Table #2: Raw Data Table of the Reaction of mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Time ±1 (s) Mass Trial #1 ± 0.10 (g) Mass Trial #2 ± 0.10 (g) Mass Trial #3 ± 0.10 (g) * Due to the space constraint, the data shown above is the not the full data, it has been condensed (to every 30s). In addition, although this cannot be seen from the table above, all of the data has reached a plateau.

7 Table #3: Raw Data Table of the Reaction of mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Time ±1 (s) Mass Trial #1 ± 0.10 (g) Mass Trial #2 ± 0.10 (g) Mass Trial #3 ± 0.10 (g) * Due to the space constraint, the data shown above is the not the full data, it has been condensed (to every 30s). In addition, although this cannot be seen from the table above, all of the data has reached a plateau. Table #4: Raw Data Table of the Reaction of mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Time ±1 (s) Mass Trial #1 ± 0.10 (g) Mass Trial #2 ± 0.10 (g) Mass Trial #3 ± 0.10 (g)

8 Time ±1 (s) Mass Trial #1 ± 0.10 (g) Mass Trial #2 ± 0.10 (g) Mass Trial #3 ± 0.10 (g) * Due to the space constraint, the data shown above is the not the full data, it has been condensed (to every 30s). In addition, although this cannot be seen from the table above, all of the data has reached a plateau. Table #5: Raw Data Table of the Reaction of mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Time ±1 (s) Mass Trial #1 ± 0.10 (g) Mass Trial #2 ± 0.10 (g) Mass Trial #3 ± 0.10 (g)

9 Time ±1 (s) Mass Trial #1 ± 0.10 (g) Mass Trial #2 ± 0.10 (g) Mass Trial #3 ± 0.10 (g) * Due to the space constraint, the data shown above is the not the full data, it has been condensed (to every 30s). In addition, although this cannot be seen from the table above, all of the data has reached a plateau. Table #6: Qualitative Observations during the Experiment Process The mixture turns grey in colour. Qualitative Observations Evidences showing that the mixture is reacting, are fizzing and bubbling. The mixture turns opaque in transparency. Smoky gases and water vapours were formed during the reaction. The beaker became warm during and after the reaction, which means heat is another product of the reaction exothermic. Units like mg are too small and precise to measure a source of error. There s always remaining precipitate and liquid in the beaker that get reused in the next trial another source of error.

10 DATA PROCESSING Sample Calculations Average Reaction Rate of 50.00mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Mass Trial #1 Average Reaction Rate = (Initial Mass - Mass after Reaction) Time Taken = (72.41g g) 165s = 0.07g 165s = 70.00mg 165s = 0.42 mg/s Average Reaction Rate of 50.00mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Mass Trial #2 Average Reaction Rate = (Initial Mass - Mass after Reaction) Time Taken = (69.10g g) 180s = 0.10g 180s = mg 180s = 0.56 mg/s Average Reaction Rate of 50.00mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Mass Trial #3 Average Reaction Rate = (Initial Mass - Mass after Reaction) Time Taken = (71.42g g) 150s = 0.10g 150s = mg 150s = 0.67 mg/s

11 Increment Average Reaction Rate of 50.00mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) All Trials Average Reaction Rate = (Sum of All Trials Reaction Rates) Number of Trials = (0.42mg/s mg/s mg/s) 3 = 1.65mg/s 3 = 0.55 mg/s Upper Range of Average Reaction Rate of 50.00mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Upper Range = Highest Average Reaction Rate - Average Reaction Rate = 0.67mg/s mg/s = 0.12 mg/s Lower Range of Average Reaction Rate of 50.00mg MnO2 (±2.00mg) + 25mL H2O2 (±2mL) Lower Range = Average Reaction Rate - Lowest Average Reaction Rate = 0.55mg/s mg/s = 0.13 mg/s

12 Processed Data Table #7: Processed Data Table of the Average Reaction Rate of the Decomposition of Hydrogen Peroxide (H2O2) in the Presence of Manganese (IV) Oxide (MnO2) Amount of H2O2 ±2 (ml) Amount of MnO2 ± 2.00 (mg) Average Reaction Rate ± 0.01 (mg/s) Trial 1 Trial 2 Trial 3 Average Upper Range (mg/s) Lower Range (mg/s) Figure #1: Average Reaction Rate of the Decomposition of Hydrogen Peroxide (H2O2) in the Presence of Manganese (IV) Oxide (MnO2) Average Reaction Rate of the Decomposition of Hydrogen Peroxide (H2O2) in the Presence of Manganese (IV) Oxide (MnO2) Average Reaction Rate (±0.01mg/s) y = E-5x x Amount of MnO2 (±2.00mg)

13 Data Analysis While processing the collected data, I have noticed a trend that the average reaction rate of Hydrogen Peroxide and Manganese (IV) Oxide reached its highest point when the amount of catalyst is 150mg. The two lowest average reaction rates, surprisingly, are seen when the amount of catalysts is 50mg and 250mg. As a result, the relationship between the amount of catalysts and the reaction rates cannot be described as a direct proportional relationship. What we see from Figure #1 is more likely a parabola - a quadratic polynomial trendline. Therefore, with the use of the parabola and the given equation above (generated automatically), we can find out the vertex of the parabola, which will give us a better understanding of the relationship between Hydrogen Peroxide and Manganese (IV) Oxide (catalyst). Figure #2: Calculations of the Parabola s Vertex (Parabola from Figure #1) Formula of a Quadratic Equation in General Form: [ax^2 + bx + c] Formula of Vertex s x-value for a Quadratic Parabola: [-b 2a] Given that the quadratic equation of the parabola is: [y = E-5x^ x ]. We can find out the vertex s x-value by subbing values into [-b 2a]. x = -b 2a = -(0.0194) 2(-5.686E-5) = = or (in my data format) Now we have the vertex s x-value, we can simply sub it into the original quadratic equation to find out its corresponding y-value. (To make it more accurate, I would sub in as the x-value). y = E-5x^ x = E-5( )^ ( ) = or 1.42 (in my data format) Therefore, the vertex, also known as the maximum value, would be (170.59, 1.42).

14 From Figure #2, we can see that the vertex has as its x-value, as well as 1.42 as its y- value. In this case, with the x and y axis I ve set for Figure #1, 1.42 would represent the maximum average reaction rate (mg/s) that could be reached, and would be the corresponding amount of catalyst (mg) that is required for such reaction rate to be reached. During the data collection process, there was no unusual results showed. From the results of three trials per increment, I noticed that multiple trials have provided similar results, despite that there is still a few outliers. As an example, from Table #7, when the amount of Manganese (IV) Oxide is 250mg, the average reaction rates are 1.04mg/s, 1.04mg/s, and 1.21mg/s respectively; the outlier would be 1.21mg/s, with a difference of 0.17mg/s. Regarding to the upper ranges and the lower ranges of the results, I ve noticed that the largest difference between the trial results and the average is 0.40mg/s and the smallest difference is 0.06mg/ s. The upper ranges and lower ranges that shows as error bars in Figure #1 might make the data seem unreliable and inaccurate, but it s not, since the unit being used for the lab is milligram per second (mg/s). This is a very small and precise unit for reaction rates, and it could be easily affected by any careless observational errors or human errors that relates to time (in seconds) and mass (in milligrams). Therefore, I would still claim my data as reliable and accurate. CONCLUSION As shown at the beginning of the lab report, the research question for this lab is: How does the amount of catalyst affect the decomposition of hydrogen peroxide? From the data that I ve collected and processed, especially from Figure #1 and Figure #2, I ve observed the fact that the amount of catalyst affects the decomposition of hydrogen peroxide by increasing the average reaction only to a certain point; after the particular point, the average reaction rate began to decrease. In this case, with only 25mL of hydrogen peroxide, I observed that the average reaction rate continues to increase till the point which mg of catalyst are added; after inputting mg, the catalyst is no longer effective anymore, as it starts to decrease the average reaction rate. As stated in most of the sources, increasing the amount of catalysts would speed up the reaction (The Effect of Catalyst). From my lab outcome, Figure #1, we can see that catalyst does increase the average reaction rate, but it only remains effective till the point where mg of catalyst is inserted into 25mL of Hydrogen Peroxide. After that particular point/amount of catalysts, the average reaction rate starts to decrease as more catalyst is added. Possibilities that could ve caused the decrease phenomenon to occur, would be that there s no more reactants in the solution after the decomposition. Through the decomposition process, products like oxygen get produced and leaves the solution (H2O2 > H2 + O2), which thereafter reduces the amount of reactants in the solution. Referring to the Collision Theory, as the solution H2O2 becomes less concentrated, fewer H2O2 would be able to collide with the catalyst and decompose (Rate). With a higher concentrated catalyst, the

15 reaction continues reluctantly and lasts for a longer time, hence decreases the overall average reaction rate. My hypothesis of the lab is: If a higher amount of catalyst is mixed with hydrogen peroxide, then the average rate of reaction (measured using mass change over time taken) will increase as well, because the catalyst is a substance that provides an alternative route for the reaction with a lower activation energy, resulting with an increase in the average reaction rate. From the data I ve collected, it has proven that my hypothesis is not completely true. To be precise, inputting catalyst does increase the average rate of reaction to a certain extent, but after a specific amount of catalysts, the catalysts are no longer that effective, and eventually the average rate of reaction begin to decrease. In this case, referring to Figure #1 and Figure #2, the average rate of reaction only increases till 1.42mg/s (with mg), and starts decreasing afterwards. EVALUATING THE INVESTIGATION There are three significant procedural weaknesses for this lab. First of all, it s the missing steps of Pour Hydrogen Peroxide into the graduated cylinder and Drop 25mL of Hydrogen Peroxide with a disposable pipette. Without the two steps, readers that follow the method would simply pour 25mL of Hydrogen Peroxide directly into the beaker, without knowing the actual amount that is being poured in, in which would definitely affect the outcome experimental results. Adding the two steps above would enhance the method and make sure that the beaker is really having 25mL of hydrogen peroxide (not 26mL nor 24mL). This would also ensure the reliability and accuracy of the data being collected. Secondly, the other procedural weakness for this lab would be the missing step after the reaction stopped, which is Clean the beaker and make sure there is no catalyst remain in the beaker. The step would prevent readers from leaving bits of catalysts in the beaker and reuse it for their next trial; since the remaining catalyst would continue to function like the way it is, affecting the average rate of reaction. Last but not least, another weakness of my method is that it does not mention any safety precautions. For this lab in particular, I should be warning anyone that follows the method to be aware for hydrogen peroxide, since it s an irritant and the reaction produces flammable oxygen gas. Therefore, including precautions or safety warnings in the method would make it a better procedure for one to follow. The current method does produce a fairly reliable and valid data, since the method is designed with controlled variables. This ensures that there are sufficient data being collected, as well as ensuring that the data is capable of answering my research question.

16 IMPROVING THE INVESTIGATION To improve the investigation, I would have to implement several modifications to the method. First of all, I would be adding some steps that are involved with measuring the amount of Hydrogen Peroxide, such as Pour Hydrogen Peroxide into the graduated cylinder and Drop 25mL of Hydrogen Peroxide with a disposable pipette. This would improve the overall reliability and accuracy of the data I have collected, as well as reducing the possibility of having any observational or human errors (like meniscus). Second of all, I would add the step Clean the beaker and make sure there is no catalyst remain in the beaker right after the step which the reaction stopped. This would also ensure reliable and accurate data being collected. Lastly, I would include precautions and/or safety warnings into the method, in order to raise people s awareness that hydrogen peroxide is an irritant, and it reaction actually produces flammable oxygen gas. This is something that I would definitely be doing for my next lab report. For further investigations, I would investigate further by adding 300mg, 350mg, and 400mg of catalysts into 25mL of hydrogen peroxide; I would observe whether the average reaction rate continues to decrease, or whether it simply goes levelled off. Alternatively, I would also try to modify my dependent variable from average reaction rate to instantaneous reaction rate. I would change my method - instead of collecting data until there s a plateau (which takes over 10 minutes), I would stop my data collection at 180 seconds so that it s going to be easier for me to figure out the instantaneous rate. Changing the dependent variable to instantaneous reaction rate and modifying the method would expand the investigation and would allows me to understand further in the effects/functions of catalysts in reactions. WORK CITED "The Effect of a Catalyst." Boundless. Boundless. Web. 15 Mar "The Effect of Catalysts on Rates of Reaction." Chemguide. Chemguide. Web. 15 Mar "Rate of Reaction." Chem4Kids.com. Chem4Kids. Web. 15 Mar