Chemistry Lab Report

Question REFERENCES =Ebbing D. & Gammon S. D. (2010). General chemistry. (9th ed. ed.). Belmont: Brooks/Cole Pub Co. (chapters 7 and 8) Report needs at least one Graph and data Table as required to display data. Spectrophotometer Lab Report Spectrophotometers are instruments that measure the amount of light absorbed by molecules in a solution for a given wavelength. In this exercise you will measure the Percent Transmission (%T) of a light through a pink cobalt chloride solution of varying dilutions with water. From that data & graph you will determine the concentration of an unknown solution. Now what do you do? 1. Open ChemLab and select ?Spectrophotometer Lab? when prompted. 2. Read through the Introduction in BOTH the course and in ChemLab. Some labs include some modification from the ChemLab instructions and if so these modifications will be listed in our course with each lab. 3. Follow the Procedure as outlined in ChemLab. 4. Perform the lab collecting the indicated data as noted in the observations section (create your own data table within your lab report collecting the specific data from this list). 5. Perform the various calculations with your collected data as listed in the lab?s observations section and if you are given a sample of cobalt solution with a reading of 44.7% transmittance with no dilution. You must report the concentration of this sample in your report & you must construct an absorbance vs. concentration graph (in MS Excel as an x-y scatter plot with a trendline& equation of the line included on the graph) to determine the concentration of this solution. 6. Write a lab report of the lab within MS Word. (There is a ?Sample Lab Report? and ?Lab Report Instructions? files in week 1?s course folder). 7. Submit your lab report by the milestone due date. LabIntroduction: Spectrophotometers are instruments that measure the amount of light absorbed by molecules in a solution for a given wavelength. In this exercise you will measure the Percent Transmission (%T) of a light through a pink cobalt chloride solution of varying dilutions with water. According to the Beer-Bouger Law the quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is directly proportional to the concentration of the substance and the path length of the light through the solution. Beer?s law is commonly written in the form A=(epsilon)cl where A is the absorbance c is the concentration in moles per liter l is the path length in centimeters* and epsilon is a constant of proportionality known as the molar extinction coefficient. The law is accurate only for dilute solutions; deviations from the law occur in concentrated solutions because of interactions between molecules of the solute the substance dissolved in the solvent. The terms percent transmittance and absorbance are used to describe spectrophotometric analysis. Percent transmittance (T) is the ratio the amount of light passing through the sample to the amount of light applied to the sample multiplied by 100.:% T = [(light passing through the sample) / (light shined on sample) ]X 100Absorbance (A) or Optical Density (O.D.) is directly proportional to concentration of solute and it represents the logarithm to the base 10 of the reciprocal of the transmittance. O.D. can be derived from % T according to the following formula:O.D. = 2 – log10 of % Transmittance *Note: the path length is given to be equal to 1 cm for the spectrophotometer arrangement in ChemLab. Lab Procedure: Step 1: Obtain a Spectrophotometer from the equipment menu set the wavelength to 510 nm. Note: the sample for the spectrophotometer is held by a cuvette which is displayed as part of the spectrophotometer by ChemLab. Step 2: Select the Spectrophotometer and add 10 ml of 0.001 M Cobalt Chloride solution from the Chemicals dialogbox. To insert the cuvette into the spectrophotometer select it and use the spectrophotometer insert procedure from the procedures menu (or use right mouse context menu). Step 3: Record the Percent transmission from the Spectrophotometer in the observation window. Remove the cuvette sample from the Spectrophotometer and empty the cuvette. Step 4: Prepare a diluted solution (1:10) of Cobalt Chloride. Add 10 ml of Cobalt Chloride to a 100 beaker. Then dilute with 90ml of distilled water. Step 5: Extract 10 ml of the (1:10) diluted solution with the 10 ml pipette and place in Spectrophotometer?s cuvette and insert the sample in the Spectrophotometer and record the % Transmission in the observation window. Remove the cuvette sample and empty the cuvette. Step 6: Prepare a diluted solution (1:100) of Cobalt Chloride. Using a 10 ml pipette extract 10 ml of the (1: 10) diluted solution from the beaker (step 4). Release the contents from the pipette into a new 100 ml beaker and dilute with 90 ml of distilled water. Step 7: Extract 10 ml of the (1:100) diluted solution with the 10 ml pipette and place in Spectrophotometer?s cuvette and insert the sample in the Spectrophotometer and record the % Transmission in the observation window. OBSERVATION SHEET BEGIN Observations: Undiluted solution: Reading From Beaker: Water H?O (Liquid) (1.000000e+01 g) (5.550930e-01 moles) Cobalt ChoridehexahydrateCoCl? (6H?O) (In Solution) (2.379300e-03 g) (1.000000e-05 moles)I?m Not sure why the values from the Beaker and the values from the Spectrophotometer are different. If it these values are important use the Spectrophotometer values. Reading From Spectrophotometer: Water H?O (Liquid) (1.000000e+01 g) (5.550930e-01 moles)Cobalt ChoridehexahydrateCoCl? (6H?O) (In Solution) (2.379300e-03 g) (1.000000e-05 moles) % Transmission of Cobalt Chloride:31.62% OD of undiluted solution (OD = 2 ? log10 (%T)):O.D. = 2 – log10 of % Transmittance = -29.62(Please Double Check My Math) Diluted solution (1:10): Reading From Beaker: Water H?O (Liquid) (7.000000e+01 g) (3.885651e+00 moles) Cobalt ChoridehexahydrateCoCl? (6H?O) (In Solution) (1.665510e-03 g) (7.000000e-06 moles)I?m Not sure why the values from the Beaker and the values from the Spectrophotometer are different. If it these values are important use the Spectrophotometer values. Reading From Spectrophotometer: Water H?O (Liquid) (1.000000e+01 g) (5.550930e-01 moles)Cobalt ChoridehexahydrateCoCl? (6H?O) (In Solution) (2.379300e-04 g) (1.000000e-06 moles) % Transmission of Cobalt Chloride:89.13% OD of undiluted solution (OD = 2 ? log10 (%T)):O.D. = 2 – log10 of % Transmittance = -87.13(Please Double Check My Math) Diluted solution (1:100): Reading From Beaker: Water H?O (Liquid) (8.000000e+01 g) (4.440744e+00 moles) Cobalt ChoridehexahydrateCoCl? (6H?O) (In Solution) (1.903440e-04 g) (8.000000e-07 moles)I?m Not sure why the values from the Beaker and the values from the Spectrophotometer are different. If these values affect the report use the Spectrophotometer values or let me know. Reading From Spectrophotometer: Water H?O (Liquid) (1.000000e+01 g) (5.550930e-01 moles)Cobalt ChoridehexahydrateCoCl? (6H?O) (In Solution) (2.379300e-05 g) (1.000000e-07 moles) % Transmission of Cobalt Chloride:98.86% OD of undiluted solution (OD = 2 ? log10 (%T)):O.D. = 2 – log10 of % Transmittance = -96.86(Please Double Check My Math) OBSERVATION SHEET END Components of the Lab Report 1. Title Page (1 points) o The title of the experiment. o Your name o Your instructor’s name. o The date the lab was performed or the date the report was submitted. 2. Title (2 points) The title says what you did. It should be brief (aim for ten words or less) and describe the main point of the experiment or investigation. An example of a title would be: “Effects of Ultraviolet Light on Borax Crystal Growth Rate”. If you can begin your title using a keyword rather than an article like ‘The’ or ‘A’. The title must be more precise than that found in Model Science. 3. Introduction / Purpose (5 points) The introduction needs to provide a clear statement of the problem or project being studied. One needs to provide concise and appropriate background of the problem and its significance. Having provided background into the problem one can then provide a basis for doing the current experiment. This is where a hypothesis is presented. Usually the Introduction is one or two paragraphs. Briefly summarize how the experiment was performed state the findings of the experiment and list the conclusions of the investigation. Introduce the equation(s) you will use and define all terms. If you are running reactions you should provide the balanced equation(s). 4. Materials (2 points) List everything needed to complete your experiment. When using solutions you must include the concentration of the solution. 5. Experimental Methods (5 points) Describe the steps you completed during your investigation. This is your procedure. Be sufficiently detailed that anyone could read this section and duplicate your experiment. Write it as if you were giving direction for someone else to do the lab. It may be helpful to provide a Figure to diagram your experimental setup. DO NOT COPY FROM THE ?LAB BOOK?. 6. Data (5 points) All your data is reported in tables. This includes the starting material and any data taken from then on. Some tables are provided in the prelab. (A graph does not substitute for the data table.) If you make up solutions you need to report how you made up the solution. Unknown numbers must be provided. Units must be included. If the balance reads to the hundredths you record to two places after the decimal. 50 g ? 50.00 g Numerical data obtained from your procedure is presented in a table. Data encompasses what you recorded when you conducted the experiment. It is just the facts not any interpretation of what they mean. It also includes observations (color change odors precipitates etc.) The table must contain the amount of starting materials any values obtained during the experiment and the values at the end of the experiment. A specific example would be the amount of and concentration of potassium iodide solution used in the Reactions Experiment the mass of the watch glass and the mass of the watch glass with the lead (II) iodide product. Another example in the Reaction Experiment would be the mass of Mg used the amount and concentration of HCl and the listing of the final products with their information that is pertinent to the write up. 7. Results (20 points & this includes the quality of your graphs and figures) Discuss in words the raw data in the RESULTS section. You look at the data and formulate a generality. What does it mean? Interpret the data. For the first lab precision and accuracy should be part of this discussion. Do not discuss the results of any calculation in the RESULTS section. Do not put the data in paragraph form i.e. read the tabulated data back to the reader. A figure diagram or graph is required. Do not put a graph in the report unless you do something with it. There is nothing to graph in the first experiment. Each graph diagram or figure needs to be labeled with a descriptive title and discussion/explanation. There are videos in the lessons showing you how to graph if you forgot. (The values in the video tables are different than your values.) Graphs required in our labs are linear graphs. They will be done in EXCEL with the equation of the trend-line shown. There are videos to refresh your memory available in the lessons. Label the axes on a graph being sure to include units of measurement. The independent variable is on the X-axis. The dependent variable (the one you are measuring) is on the Y-axis. Be sure to refer to figures and graphs in the text of your report. The first figure is Figure 1; the second figure is Figure 2 etc. Calculations and any discussion of the calculated results go into the ANALYSIS and DISCUSSION section. 8. Analysis and Discussion (40 points) This section is where you include the equations in a logically explained order with a discussion interpreting the results of your calculations. What do the calculations show? What do the results mean? Interpret them. The Analysis part contains any calculations you made based on the numbers in the Data table. You must show all work. o Show the equation(s) used o Be sure all numbers have units. All types of calculations must be shown. Do not put them in paragraph form. Learn to use equation editor. Use the correct parentheses and brackets. Write the equation then inert your numbers. Units must be included in the equations and in your final result. If you must perform the same calculation for multiple points you must do a sample calculation for at least one. Show all work. Your answer must have units or it is incorrect. This is where you perform your calculations interpret the results and determine whether or not a hypothesis was accepted. This is also where you would discuss any mistakes you might have made while conducting the investigation. You may wish to describe ways the experiment might have been improved. Percent yield or percent error is always calculated. You will have to find the literature value. (Use the internet for the literature value.) This section is no shorter than ? page long. Do not write in words the data in the table for a discussion. The reader can easily read the table. Do not re-write the experimental methods for a discussion. 9. Conclusions (12 points) Most of the time the conclusion is two paragraphs that sum up what happened in the experiment whether your hypothesis was accepted or rejected and what this means. The purpose of this section is to put the interpretation of the data into the context of the original problem based on the evidence presented in the report. This includes briefly restating the purpose of the lab and listing the end results (numbers). 10. References (5 points) If your research was based on someone else’s work or if you cited facts that requires documentation then you should list these references. Model Science with the version number will always be a reference. It is your lab manual. 11. Paste the ?observation sheet? at the end of your report. (3 points) The observation sheet is not your data table.

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