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Objectives
- Conduct laboratory work in compliance with guidelines for personal lab safety and responsible management of chemical waste; this includes appropriate use of personal protective equipment and interpretation of Globally Harmonized System for Hazard Communication (GHS) labels.
- Measure quantities such as mass, volume, temperature, and absorbance with proper technique, and record the results of measurements with the appropriate number of significant figures and units.
- Record observations of chemical processes (such as precipitate formation, gas evolution, etc.) and write chemical reactions consistent with their observations.
- Demonstrate proper techniques for laboratory procedures, such as titration, filtration, solution preparation, spectrophotometric measurements, etc.
- Demonstrate proper use of glassware and equipment, including beakers, Erlenmeyer flasks, volumetric pipets, burets, volumetric flasks, watch glasses, graduated cylinders, filtration apparatus, single-beam spectrophotometer, pH meter, balances.
- Communicate lab procedures, observations, and results in a laboratory notebook, written reports, and verbal presentations effectively.
- Interpret and analyze qualitative observations and quantitative results, incorporating graphs and tables as appropriate.
- Identify errors and explain their effect on experimental data.
- Design an experimental procedure.
- Apply knowledge of scientific theories to problem-solving applications.
- Develop a hypothesis for a scientific experiment.
- Identify the control, independent, and dependent variables for an experiment.
- Predict the next steps for a scientific study using collected data.
- Draw conclusions based on experimental data.
- Calculate pH and hydronium concentration of a solution.
- Utilize the Henderson-Hasselbach equation to create a buffer solution at a specific pH.
- Make an aqueous solution at a specific concentration.
- Identify acid-base conjugate pairs.
- Discuss the results of an experiment in oral and written formats, including predictions, graphs, and calculations.
- Research and complete an analysis of scientific findings on a current topic in chemistry.
Introduction
Please read section 14.6 of your textbook on buffers, paying special attention to the information Henderson-Hasselbalch equation. The Henderson-Hasslebalch equation relates pH of a buffer to the concentration of the conjugate acid-base.
Figure 1: Henderson-Hasslebalch Equation
You will need the pKa value for the conjugate acid used. You can find this using the question below:
Figure 2: Formula for determining pKa from Ka
Appendix H of your textbook provides a list of Ka values for most the weak acids listed below. You may also need to look some of the Ka values up online. You can use this resource to help identify the chemicals you will need to prepare your buffer solutions. Then use the Henderson-Hasslebalch equation to determine how much of the conjugate acid-base pair you will need to create your buffer.
The pKa of each conjugate acid can be used to identify the best conjugate acid-base pair needed to make a buffer. For instance, if you want to create a buffer with a pH of 4, then choose a conjugate acid with a pKa close to 4 to make your buffer.
Experimental Procedure
Experimental Materials
1M Hydrochloric Acid
1M Sodium Hydroxide
6M Acetic Acid
Sodium acetate
Sodium Hydrogen Carbonate
Sodium Carbonate
Potassium Phosphate Monobasic (KH2PO4)
Potassium Phosphate Dibasic (K2HPO4)
Sodium Phosphate Tribasic
Sodium bisulfite
Sodium sulfite
DI Water
Glassware in your drawer
5 100-mL volumetric flasks
pH meter
pH paper
Digital Balance
Sea Shells
Plastic Pipets
Label Tape
Sharpe Marker
Paper Towels
Vortex Stirer
Timer/Clock
Experimental Purpose
The purpose of the lab is to design an experiment to investigate the impact of increasing acidity on sea shells over time.
Experiment Outline
Design a lab to test the effect of pH on sea shells. Below are some parameters for your experiment.
- Design and write a step-by-step experimental procedure. You will be provided the experimental supplies provided below. Your procedure should include all steps of your experiment, including directions on making any necessary solutions.
- You will create five aqueous buffer solutions using the chemicals provided by your instructor (4 buffer solutions and 1 DI water only). You decide on the pH of each solution; however, each solution needs to vary by at least a pH of 0.5. Record the pH of each solution at the start and each time you take the mass of the sea shells.
- All solutions should have a 0.1M concentration of solute(s).
- Use the resources provided by your instructor to select the chemicals you will use to create each solution. Include all of your calculations in your lab notebook.
- You must collect at least 6 data points for each tested sea shell. There are multiple ways you can time your experiment; however, Google Chrome does offer a timer option that you may find useful.
NOTE: You may not need to use all of these supplies. That is okay. You may find you need additional supplies to complete the experiment. If you need additional supplies beyond this list, please talk with your instructor to obtain them.
You will not be given any chemicals beyond the ones included in the list above for the experimental materials.
Before leaving lab today, you need to:
- Write your hypothesis for this experiment.
- Identify the control, dependent, and independent variables.
- Identify the control sample.
- What qualitative and quantitative data are you collecting in this lab? (Hint, you should have both forms of data.) List the data you will be collecting at the start, during, and at the end of the lab.
- A list of the specific materials you need for the experiment.
- Write your experimental procedure. Please type your experimental procedure. Then, you and your partner can print it and paste it into your lab notebooks.
- Please email all of the above information to your instructor so she can review it, offer you notes, and help you make sure your procedure will address the purpose of the experiment appropriately. CC your lab partner(s) when you send the email. Your instructor will reply all with her feedback.
Before Next Week’s Lab:
- Copy/paste your experimental procedure into your lab notebook.
- Draw a table in your experimental notebook to collect your data.
- Calculate the amount of acid and base you need to create the 4 buffer solutions you will use in your experiment. Include your calculations for making your solutions in your lab manual. I recommend creating a table or otherwise listing out how to make each solution before coming to class. The clearer and more organized your solution information, the easier it will be for you to create your solutions.
Post Lab Assignment
- Graph your lab data for each of your samples. You want to graph your dependent variable vs. time for each sample. Your graph should have a total of 5 lines. Include the R2 value and equation for each line. Title your graph and label the axes and samples. Paste this in your lab notebook.
- Write up your discussion and conclusion in your lab notebook. Be sure to note if you reject or accept your hypothesis and why.
- Submit your data table and a minimum 200-word typed summary of your observation/findings and if you accept/reject your hypothesis and why to your lab instructor at the start of the following lab period. This table/summary is how you earn your 25 points for this lab.
Ensure you have your information for this experiment in your lab notebook. You will write a lab report over your experiment and findings.
Lab Report
You must write a lab report on the experiment and your results. Please see the guidelines on How to Write a Lab Report. The due date for this assignment is noted on the semester schedule.
Below is some experiment-specific information you will need to include in your report:
- The experimental procedure and a complete list of experimental supplies. Be sure to include any updates you made to your procedure while you conducted your experiment. Since you wrote this portion of your experiment, this section will be worth more points than on previous lab reports. Take the extra time to ensure its complete and clear.
- A data table(s) outlining your results/data.
- Formulas and sample calculations from the experiment.
- Include the graph you created using your data. Your graph should include the equation and the R2 value for the line.
- Discuss the accuracy and precision of the data points you collected. If you chose to throw out a data point, explain why.
- What do your results tell you about ocean acidification’s impact on animals with shells?
- You will also want to use one peer-reviewed journal article as a resource for your introduction. You will need to find this source, but since you have been researching OA all semester, you likely already have a resource you can use. Also, cite any other resources you used to write your lab report.
Remember that this is your research and you are the expert on what you did in the lab. Write this report as if you are reporting your results to other scientists.
A rubric for this formal lab report can be found on Brightspace if you go to Assignment → Rubrics → Ocean Acidification Lab Report Rubric.
References
This page was published on February 1, 2024 and last updated on March 18, 2024.
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