Scientific Measurement and Lab Skills
At the end of this lab, students should know...
How can you visualize the relationship between two measured variables?
To display the relationship between two variables, plot the data points with the dependent variable on the y-axis and the independent variable on the x-axis. This is called a two-dimensional graph.
How can you tell whether a variable is independent or dependent?
The variable that you want to be able to predict based on another variable is t...
Source: Smaa Koraym at Johns Hopkins University, MD, USA
- Preparation of the Laboratory
Here, we show the laboratory preparation for 10 students working individually, with some excess. Please adjust quantities as needed.
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To set up for this lab experiment, wear the appropriate personal protective equipment, including a lab coat, chemical splash goggles, and gloves.
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Prepare a 1.5 x 10-5 M erythrosin B red dye solution. To prepare 500 mL of this solution, weigh 0.0066 g of erythrosin B on an analytical balance.
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Transfer the erythrosin B to a 250-mL Erlenmeyer flask. Then, measure 200 mL of deionized water and add it to the flask. Place a magnetic stir bar in the flask, set the flask on a stir plate, and mix the solution until it appears homogeneous.
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Use a funnel to pour the solution into a 500-mL volumetric flask, and carefully fill the flask to the line using deionized water. Seal the top of the flask with paraffin film and invert it several times until the solution is well-mixed.
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Label a 500-mL squeeze bottle with the concentration and transfer the solution into the bottle. Store the bottle on a mat in the hood. Note: Take significant figures into account.
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Place acetone in an area so that students have access to it during the lab. Note: Each student will need about 40 mL.
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Set weigh boats, scoops, and a container of sand next to a balance. Note: Each student will need about 3 g.
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Place an organic waste container in a central hood.
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Set out the following glassware and equipment at each student lab station (we suggest students work independently during this lab):
150-mL beaker 1100-mL beaker 1250-mL beaker 1400-mL beaker 1600-mL beaker 1500-mL filter flask 1Büchner funnel 110-mL graduated cylinder 1Watch glass 15-mL volumetric pipette 110-mL volumetric pipette 110-mL capacity pipetter 110-mL volumetric flask 1String (18 in) 1Silicone vacuum tubing (18 in) 112-in ruler 1Rubber adapter 1Rubber stopper 1Glass stirring rod 1Rubber policeman 1Disposable pipette 1Bottle of deionized water 1Lab mat 1Box of filter papers (1 filter paper per student)
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View the full transcript and gain access to JoVE Lab Manual videos
Q1: What personal protective equipment should you wear when preparing a laboratory?
Wear a lab coat, chemical splash goggles, and gloves to protect yourself from chemical hazards during solution preparation. These items shield your skin, eyes, and clothing from potential splashes or spills when handling reagents like erythrosin B dye and other chemicals throughout the experiment.
Q2: How do you prepare a 1.5 × 10⁻⁵ M erythrosin B solution?
Weigh 0.0066 g of erythrosin B on an analytical balance and transfer it to a 250-mL Erlenmeyer flask. Add 200 mL of deionized water, stir until homogeneous, then transfer to a 500-mL volumetric flask and fill to the line with deionized water. Invert several times to ensure thorough mixing and proper concentration.
Q3: Why is a volumetric flask used when preparing solutions?
A volumetric flask ensures precise solution concentration by allowing you to fill to an exact volume mark with accuracy. This precision is critical for reproducible experimental results, especially when preparing dilute solutions like erythrosin B dye at specific molarity concentrations for consistent lab outcomes.
Q4: What glassware and equipment should be set up at each student lab station?
Each station requires beakers (50, 100, 250, 400, 600 mL), a 500-mL filter flask, Büchner funnel, graduated cylinders, volumetric pipettes, volumetric flask, watch glass, stirring rod, rubber policeman, and filter paper. Additional items include tubing, ruler, rubber adapter, stopper, string, and disposable pipette for independent student work.
Q5: How should you store the prepared erythrosin B dye solution?
Transfer the solution into a labeled 500-mL squeeze bottle indicating its concentration and store it on a mat in the hood. This storage method protects the solution from light exposure and contamination while keeping it accessible for student use during the experiment.
Q6: What materials should be prepared for student access during the lab?
Place acetone in an accessible area, with approximately 40 mL per student. Set out weigh boats, scoops, and sand (about 3 g per student) next to a balance. Position an organic waste container in a central hood for safe disposal of chemical materials used throughout the experiment.