As much of the world remains affected by COVID-19, some schools remain in virtual or hybrid learning structures for the fall semester. These modified learning environments have significantly restricted classroom laboratory work. Since my school is operating entirely online, I put together a series of virtual laboratory experiments that follow a framework described in a previous ChemEd X post: A Virtual Lab Format for Online Teaching During COVID-19

Here, I’d like to share my first virtual lab activity in this format. In this investigation, students learn about density through a combination of video demonstrations and PhET simulations.

significant figures, particulate level, equipment, how to use a balance, how to use a graduated cylinder, how to analyze the data

additional vocab: intensive & extensive, quantitative & qualitative

This can be done in one class period. The extension "at home" section would require about 30 minutes.

Section 1 and 2 only require videos and PhET simulations. Section 3 (at-home investigation) requires a 100-mL graduated cylinder (available at amazon or home brewing supply stores), a kitchen scale (preferably with at least 0.1 g precision), tap water, 10 pre-1982 pennies & 10 post-1982 pennies

Students work through the * Density - Virtual Lab* assignment document (found in the Supporting Information) as described below. The document includes all of the required links to videos and PhET simulations.

### Section 1 - Defining Density

First, students learn about the concept of density by way of an instructional video tutorial (video 1). I offer a simple demonstration that compares the density of water, oil, and a metal coin to begin to consider density through particulate representation.

* Video 1: *Virtual Chemistry Experiment: Exploring Density Part 1

*on The Science Classroom YouTube Channel (Published 9/2/2020)*

After this introduction, students use the PhET simulation, *States of Matter Basic*, to observe solids, liquids, and gases at the particulate level (image 1). Then, students answer a few analysis questions to deepen their thinking about density.

**Image 1:** "States of Matter Basic" PhET simulation (accessed 9/15/2020)

### Section 2 - Determining Density

Next, students watch a second instructional video tutorial to learn how to experimentally determine the density of a collection of pennies (video 2). This video focuses on equipment and technique to learn how to use a balance and a graduated cylinder. I also describe how to analyze the data, using the measured mass and volume to calculate the pennies’ density.

* Video 2: *Virtual Chemistry Experiment: Determine Density (Part 2),

*on The Science Classroom YouTube Channel (Published 9/3/2020)*

After watching the video, students use the PhET simulation, *Density*, to experimentally determine the density of the five mystery objects (image 2).

**Image 2:** "Density", PhET simulation (accessed 9/15/2020)

### Section 3 - Try it at Home

In general, the video demonstrations use simple household materials and should be safe to complete at home. The last section of the virtual lab activity includes a straightforward lab sheet so that students can attempt experiments on their own. This section is optional since students may not have access to all of the materials necessary to carry out the procedure.

*For the most part, these activities are easy to carry out in a virtual classroom setting. However, minor technical difficulties can always occur when using computer simulations. The second simulation, Density, uses Flash (link: https://get. adobe.com/flashplayer/about/) which may not run properly unless your computer is updated with the latest version. I recommend setting a small portion of class time for troubleshooting technical issues. Thankfully, PhET’s website includes a beneficial help center for this purpose. *

**See the Density - Virtual Lab Student Document in the Supporting Information..**

Post the student pdf for students to access and complete.

## Safety

### General Safety

General Safety

**For Laboratory Work:** Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016).

**For Demonstrations:** Please refer to the ACS Division of Chemical Education Safety Guidelines for Chemical Demonstrations.

#### Other Safety resources

RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies

## NGSS

Mathematical and computational thinking at the 9–12 level builds on K–8 and progresses to using algebraic thinking and analysis, a range of linear and nonlinear functions including trigonometric functions, exponentials and logarithms, and computational tools for statistical analysis to analyze, represent, and model data. Simple computational simulations are created and used based on mathematical models of basic assumptions. Use mathematical representations of phenomena to support claims.

Mathematical and computational thinking at the 9–12 level builds on K–8 and progresses to using algebraic thinking and analysis, a range of linear and nonlinear functions including trigonometric functions, exponentials and logarithms, and computational tools for statistical analysis to analyze, represent, and model data. Simple computational simulations are created and used based on mathematical models of basic assumptions. Use mathematical representations of phenomena to support claims.