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# Scientific Measurement and Lab Skills

JoVE Lab Manual
Lab: Chemistry

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Scientific Measurement and Lab Skills

# Scientific Measurement and Lab Skills

## Learning Objectives

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 the dependent variable, and the variable that the prediction is based on is the independent variable.

#### What is the sample standard deviation?

The sample standard deviation expresses the variation within a group of data points. This is relevant when you have multiple data points for the same condition, such as repeated measurements of gas volume at the same temperature. The standard deviation can also be used as an uncertainty range for calculated values.

#### How can you quantify the relationship between two variables in a two-dimensional graph?

To quantify the relationship between variables on a two-dimensional graph, use the best-fit function tool in spreadsheet or graphing software to generate the equation that best fits the data. This equation will allow you to calculate dependent values as a function of independent values.

#### How can you determine the precision of your calculated linear relationship between variables?

The coefficient of determination (R2) shows the variation between the actual dependent values and the theoretical dependent values that are calculated by plugging the independent values into the best-fit function. The closer the R2 value is to 1, the better the linear function fits the data.

## List of Materials

• Acetone (40 mL/student)
400 mL
• Sand (3 g/student)
30 g
• 50-mL beaker
10
• 100-mL beaker
10
• 250-mL beaker
10
• 400-mL beaker
10
• 600-mL beaker
10
10
• 83-mm Büchner funnel
10
10
• Watch glass
10
• 5-mL volumetric pipette
10
• 10-mL volumetric pipette
10
• 10-mL capacity pipetter
10
10
• String (18 in)
10
• Silicon vacuum tubing (18 in)
10
• 12-inch ruler
10
10
• Rubber stopper (size 15)
10
• Glass stirring rod
10
• Rubber policeman
10
• Disposable pipette
10
• 250-mL bottle of deionized water
10
• Filter paper (1 per student)
10
• Lab mats (+1 for instructor)
10
• Weigh boats
20
1
1
1
• Powder funnel
1
• Magnetic stir bar
1
• Stir plate
1
• 500-mL wash bottle
1
• Plastic paraffin film
1 roll
• Weighing paper
1
• Erythrosin B
0.0066 g
• Deionized water
500 mL
• Lab spatula
Dependent on the lab size
• Analytical balance
Dependent on the lab size

## Lab Prep

Source: Smaa Koraym at Johns Hopkins University, MD, USA

1. Preparation of the Laboratory

Here, we show the laboratory preparation for 10 students working individually, with some excess. Please adjust quantities as needed.

• To set up for this lab experiment, wear the appropriate personal protective equipment, including a lab coat, chemical splash goggles, and gloves.
• 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.
• 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.
• 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.
• 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.
• Place acetone in an area so that students have access to it during the lab. Note: Each student will need about 40 mL.
• Set weigh boats, scoops, and a container of sand next to a balance. Note: Each student will need about 3 g.
• Place an organic waste container in a central hood.
• Set out the following glassware and equipment at each student lab station (we suggest students work independently during this lab):  1    50-mL beaker 1    100-mL beaker 1    250-mL beaker 1    400-mL beaker 1    600-mL beaker 1    500-mL filter flask 1    Büchner funnel 1    10-mL graduated cylinder 1    Watch glass 1    5-mL volumetric pipette 1    10-mL volumetric pipette 1    10-mL capacity pipetter 1    10-mL volumetric flask 1    String (18 in) 1    Silicone vacuum tubing (18 in) 1    12-in ruler 1    Rubber adapter 1    Rubber stopper 1    Glass stirring rod 1    Rubber policeman 1    Disposable pipette 1    Bottle of deionized water 1    Lab mat 1    Box of filter papers (1 filter paper per student)

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