MODULE 1
Objective 1.7 Lesson D
Ensuring Accuracy
Course
Advanced
Biotechnology
Unit
Lab
Overview
Essential
Question
How do scientists collect and analyze data?
TEKS
130.364 1A,
1C, 1D, 1G,
1H, 1J, 1K, 2E,
2F, 2G, 2H, 2I,
2J
TAKS
Science 1A,
2A, 2B, 2C, 2D
Prior Student
Learning
Basic Math
Skills
Estimated
Time
120 minutes
Rationale
Different pieces of lab equipment are designed to measure properties such as temperature, pH, mass, and volume to varying degrees of accuracy. If the temperature markings on the side of a thermometer are not set accurately, the instrument’s measurements will not be accurate. The accuracy of these markings is due to the calibration, or standardization, of the thermometer.
The standards used to calibrate a thermometer are freezing and boiling water.
Some equipment must be periodically recalibrated because the settings are not as immovable as lines on a graduated cylinder or thermometer. The calibration of instruments such as pH meters, electronic balances and micropipettors can be rendered inaccurate by factors such as movement, humidity, electrical field changes, and many others.
Objective
Students will:
• Calibrate a pH meter using standard pH buffers and an SOP.
• Use a pH meter to correctly determine the pH of an unknown solution.
• Calibrate an electronic balance using standard weights and an SOP.
• Use an electronic balance to obtain a desired mass of a substance.
• Compare the measuring accuracy of glassware.
• Leave a clean lab area.
Engage
• Can anyone think of a consequence of having a scale that is “off” by 5 grams? Think of a consequence in your personal life and in the biotech community. For example: pharmaceutical companies, drug design, and so on. Project this Virtual Biotechnology Company Tour to give students and idea of the type of sophisticated equipment they will be using and why accuracy is vital.
Key Points
• Refer to Power Point from Module 1 Objective 6 and Objective 7.
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Activity
1. Students should set up the lab the previous day and complete the prelab activity.
2. Students perform Calibrating Lab Instruments Lab and complete
Calibrating Lab Instruments Post Lab .
3. While students are performing lab, ask them to perform some of the tasks listed on the Skill Standard: Calibrating and Using
Equipment and assign skill grades.
4. Depending on time, this activity leads to quite a few extensions: a. Design an experiment to test for accuracy of an instrument. b. Use previous EXCEL activity to perform statistical analysis on data collected. c. Practice entering this experiment into a scientific notebook. d. Students create their own SOP’s for designed experiments.
5. Students can add additional criteria to the skill standards that they think is important for proficiency.
Assessment
• Skill Standard: Calibrating and Using Equipment o Have students enter additional grading criteria for optional activities. o Great lab to Peer Grade
Materials
• Calibrating Lab Instruments Pre Lab
• Calibrating Lab Instruments Lab
• Calibrating Lab Instruments Post Lab
• Skill Standard: Calibrating and Using Equipment
Accommodations for Learning Differences
•
Visit the Special Populations section of the CTE Career and
Technical Education Website: http://cte.unt.edu/special-pops .
National and State Education Standards
Texas College Readiness Standards
I. Nature of Science: Scientific Ways of Learning and Thinking
A4, B1, B2, B3, D3, E1, E2
II. Foundation Skills: Scientific Applications of Mathematics
A1, A2, A5, A7, E1, F1, F2, F3
III. Foundation Skills: Scientific Applications of Communication
B1, B2, B3, B4, C1
Copyright © Texas Education Agency 2012. All rights reserved.

Name:_________________
Pre-Lab
1. What does it mean to calibrate a piece of equipment? Why is it important?
2. Go to http://www.bio-link.org/GMP/sopparts.html
. What is an SOP?
3. View the tutorials for each piece of equipment below you will be calibrating in this lab. For each tutorial you must type an SOP and list at least 2 user “tips” on using the equipment. A sample SOP is provided below*. Tape SOPs on the back of this paper to be turned in. o How to Adjust pH with a pH Meter o How to Weigh with an Electronic Balance o How to Pipet
* 5.4. Operation
5.4.1. Ensure that the desired weighing unit is displayed. If this is not so, use the configuration parameters menu to change it.
5.4.2. Place sample onto the weighing pan, close all draft shields and read off value from the LCD display.
5.4.3. If using the tare function, place empty weighing container on the weighing pan, press the TARE key and then place the sample in the weighing container
5.4.4. Close all draft shields and read off the tared value from the display.
5.4.5. Use the tare function repeatedly if necessary.
Copyright © Texas Education Agency 2012. All rights reserved.

Lab
Part A: Calibrating a pH Meter
►View
How to Adjust pH with a pH Meter
Materials
Name:_________________
Each Group: large waste beaker
Class Shares: pH meter with SOP
25 mL of a solution of unknown pH electronic balance with SOP
10 mL graduated cylinder 200 g standard mass for balance calibration
50-mL beaker with 10-mL graduations
100- or 150-mL beaker pH standard buffers for meter calibration
5 mL pipette
10 mL pipette
Pipette bulb or filler
Beral pipettes
Procedure
1. Select a pH meter to calibrate and record its model number. Turn on and calibrate the pH meter using the SOP provided. You will be using pH 7, pH 10 and pH 4 standard buffers. The manufacturer often adds color to help identify the solutions; become familiar with these characteristic colors. Buffers are used because they have very stable pH value. Remember to always rinse the pH electrode with a wash bottle of distilled water or with the next solution before using it, catching the rinse liquid in a waste beaker labeled as such. Never rinse into the electrode storage solution or buffer.
2. After calibration is complete, use the meter to measure the pH of an unknown solution. Swirl the solution slightly to ensure that it makes good contact with the electrode before recording a reading.
Record the pH on your answer sheet and have the instructor check your answer before going to the next section.
Part B: Calibrating and Using an Electronic Balance
►View
How to Weigh with an Electronic Balance
The standards used to calibrate electronic balances are objects of known mass. For balances that measure to ± 0.01g, the standard is usually a 200-gram weight. These balances are used to measure amounts over 0.05 g. When you place the 200-gram weight on the balance in calibration mode, the balance recognizes the weight as 200 grams, and will then use that information to measure other masses.
1. Dispense 50 mL of orange stock solution into a 100- or 150-mL beaker.
Tip: Never pipet from a stock solution. Rather, pour the approximate amount that you plan to use from a stock solution, and never return unused portions to the stock solution. This will prevent contamination.
Copyright © Texas Education Agency 2012. All rights reserved.

2. Select a balance and record the model number. Follow the instructions in the SOP provided for the balance model to calibrate the balance. Have the instructor look at the live readout with the 200-gram weight on the balance before moving to the next section.
3. Place a weigh boat on the balance pan and press the tare button. This subtracts the weight of the weigh boat so that you are only weighing what is put inside it.
4. Draw up 4 mL of orange water using a 5 mL pipette and pipette filler or bulb and deliver it into the weigh boat. You might need to practice drawing up and delivering the liquid back into the flask until you can do it smoothly. If these are blowout pipets, to get the most accurate measure you must blow out the last drop (see the lab equipment exercise for ways to distinguish between blowout and to deliver pipettes). If you have a pipette filler, roll the wheel up and down quickly several times; if you have a pipette bulb, squeeze the bulb after emptying the pipette. Another option is to measure 5 mL and then deliver only down to the 1 mL mark. Remember to discard the remaining liquid in your waste beaker, not back into the stock solution.
Tip: When adjusting the volume of a pipette, the bottom of the meniscus should be even with the marking to which you are adjusting. Make sure that your eye is level with the marking and meniscus in order to make sure that they are lined up correctly. Keep your pipet perpendicular to the benchtop. Make sure that there are no droplets of liquid on the outside of the pipet before you transfer it, and touch the pipet tip to the side wall of the container as you are dispensing the liquid.
5. Record the mass of the orange water in your notebook and in the analysis section. At sea level, 1.00 mL of water weighs 1.00 g. This should help you decide if your measurement was accurate.
6. Have each member of the group repeat step 4 and add 4 mL of orange water to the weigh boat (do not empty the weigh boat between measurements). Divide the total mass by the number of people in the group to find the average mass. Show calculations in your on your answer document.
Part C: Measuring Accuracy of Glassware
►View
How to Pipet
Tip: Always inspect glassware before use. This is especially important if you are handling hazardous materials or heating the glassware. Discard chipped or cracked glassware in a specially designated glass disposal box. Never throw away glassware in the trash, and never dispose of plastic pipettes or other non-glass items in the glass disposal box.
1. Create a data table for procedures below and record on answer sheet.
2. Measure 10 mL of water in a 50 mL beaker using the lines on the beaker for your measurement.
Tare a weigh boat on the balance. Pour the water in the weigh boat and record the mass in your lab notebook and on the analysis page. Each member of the group should repeat this step and record each measurement.
3. Repeat step 1 using a 10 mL graduated cylinder and repeat step 1 again with a 50 mL graduated cylinder.
4. Repeat step 1 using a 10 mL pipette.
5. Repeat step 1 using a 50 mL flask.
6. Clean up your lab station. Pour the contents of the waste beaker down the sink with plenty of water, and return dirty glassware to the cart. Wipe off your lab bench with a wet paper towel. Make sure that the balances, pH meters, and the areas around them are clean and dry, and turn off the equipment.
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D. Design and Experiment: What is the best way to measure 2.7 mL of gH2O?
You are working in a lab where you need to put 2.7 mL of dH
2
O into a test tube. One member of your group thinks it would be best to use a 5 mL pipet to measure this volume. Another member of your group thinks it would be best to use the 100 – 1000
μL micropipettor three times, measuring out 0.9 mL each time. You think it doesn’t make any difference. Design and carry out an experiment to see who is correct. Make sure you repeat each method for measuring 2.7 mL at least eight times.
E. Design and Experiment: How does incorrect use of the micropippetor affect its accuracy and precision?
According to the instructions for using the micropipettors, it is very important to press the button down to the FIRST stop when getting ready to fill the tip, and all the way down to the SECOND stop when emptying the tip. (Note: detailed instructions for using the micropipettors are in a previous lab.)
A lab tech working at a medical lab, who did not pay close attention during her cellular and molecular biology class in college, has been using the micropipettors incorrectly. Her procedure is to press the button all the way down to the second stop both when getting ready to fill the tip and when emptying the tip. Design and carry out an experiment to determine how her mistake affects the accuracy and precision of her measurements. Make sure you repeat each method for measuring (correct and incorrect) at least eight times
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Post Lab
Part A:
Unknown pH:
Teacher Initials for Correct pH of calibrated solutions:
1. Based on what you know about the pH scale, why do you think the meter was calibrated with both pH 7 and pH 4 buffers?
Part B:
Calculations:
2. What does it mean to “tare” a balance?
3. What is a blowout, or serological pipet?
4. The definition of a gram is the mass of 1 mL of pure water at 20
˚C (about room temperature) and 1 atmosphere of pressure. a) What should be the average mass of the water measured? Show your calculations. b) What was the average mass of the water your group measured? Show your calculations. c) If there is a difference between the predicted mass (A) and the observed mass (B), how can you account for it?
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Part C:
Data Table:
5. Calculate the mean, the percent error of mean, and the standard deviation for the volumes of water delivered when using the 50 mL beaker, the 10 mL graduated cylinder, the 10 mL graduated cylinder, the 10 mL pipette, and 50ml flask. Display your calculated values in a clearly labeled table. USE your EXCEL knowledge!
6. Give the table an appropriate title, and be sure to use the correct number of significant digits and appropriate units when reporting your results. a) When measuring 10 mL of dH
2
O, which measuring device seems to be more accurate, the 50mL beaker or the 10 mL graduated cylinder? Be sure to explain your answer. b) When measuring 10 mL of dH
2
O, which measuring device seems to be more precise, the 50 mL beaker or the 10mL graduated cylinder? Be sure to explain your answer. c) Use the Student’s t-test (USE EXCEL) to test the null hypothesis that there is no difference in the accuracy of the 50 mL beaker and the 10 mL graduated cylinder when measuring 10 mL of dH
2
O. Be sure to show your p value and explain your conclusions. Remember, if your data support your hypothesis you should NOT conclude that your hypothesis is correct.
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Part D:
Describe the experiment you carried out to answer the question in part E of the lab procedures on a separate sheet of paper . Display your results in a clearly labeled table. Explain your conclusions and support them by referencing your data and any statistical tests you performed. Remember, if your data support your hypothesis you should NOT conclude that your hypothesis is correct.
Part E:
Describe the experiment you carried out to answer the question in part E of the lab procedures on a separate sheet of paper . Display your results in a clearly labeled table. Explain your conclusions and support them by referencing your data and any statistical tests you performed. Remember, if your data support your hypothesis you should NOT conclude that your hypothesis is correct.
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Criteria
Use of an electric balance
Chooses appropriate glassware
Use of pH meter
Needs Improvement
1pt
Rarely / Never
Rarely / Never
Rarely / Never
Adequate
2pt
Sometimes
Sometimes
Sometimes
Adequate
3pt
Usually / Always
Usually / Always
Usually / Always
Use of pipette Rarely / Never Sometimes Usually / Always
Correctly answers analysis questions from Part A
Correctly answers analysis questions from Part B
Correctly answers analysis questions from Part C
Optional
Rarely / Never
Rarely / Never
Rarely / Never
Rarely / Never
Sometimes
Sometimes
Sometimes
Sometimes
Usually / Always
Usually / Always
Usually / Always
Usually / Always
Optional Rarely / Never Sometimes Usually / Always
Optional Rarely / Never Sometimes Usually / Always
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