Summary

In this simulation, students will investigate the effect of changing variables on both the volume and the density of a solid, a liquid and a gas sample. Students will analyze the different states of matter at the particle level as well as quantitatively. This lesson accompanies the simulation from the September 2015 issue of Chemistry Solutions.

Grade Level

High or middle school

Objectives

By the end of this lesson, students should be able to

• Understand the relationships between temperature, volume and density in a liquid and solid sample.
• Understand the effect of changing the pressure or the temperature of a gas sample on both the volume and density of the gas sample.
• Accurately calculate the final values for both volume and density of a sample based on a set of conditions.
• Predict the spatial distribution of particles in samples of solid, liquid and gas as variables are changed.
• Describe the interaction and motion of particles in samples of solid, liquid and gas as variables are changed.

Chemistry Topics

This lesson supports students’ understanding of

• Density
• Molecular Motion
• Volume
• Temperature
• Gas Pressure

Time

Teacher Preparation: 10 minutes

Lesson: 45-60 minutes

Materials

• Computer with internet access
• Calculator
• https://www.teachchemistry.org/density

Safety

No specific safety considerations are needed for this investigation.

Teacher Notes

• All particles are represented in the same manner in this simulation (both molecules and atoms are represented as spheres).
• The values shown on the controls for temperature are the same fixed amounts for solid, liquid and gas; the options are 23.0⁰C, 50.0⁰C and 90.0⁰C. The user cannot choose any other temperature value other than these.
• In the gas simulation, the user can manipulate either temperature or pressure, but not both. If the temperature is changed, the pressure with automatically become locked at 1.00atm. If the pressure is changed, the temperature will automatically become locked at 50.0⁰C.
• In all of the simulations the user can choose to display either Kelvin or Celsius units for temperature.
• Students should understand the density formula, and how to calculate density, mass and volume from the formula before using this activity.
• Students should understand the meaning of density, temperature, volume and pressure (gas only) before the activity.
• All values and calculations are reported with correct significant digits in the simulation.
• For best results students should work individually or with a partner. Larger groups should be avoided for this activity.
• Younger students may not know Kelvin units yet, so this option can be ignored if that is the case, as well as the pre-lab question regarding Kelvin.
• Answers to the student activity:
• Pre-lab Questions:

1. Student sketches should show that the particles have the least amount of space between them in the solid example, followed by more space in the liquid sample, and the gas should have the most space represented between particles.
2. Solid
3. a. Temperature is the measure of the average kinetic energy in the particles of a sample of matter at a specific time.
   b. Celsius units are often the most common measurement units used in chemistry. Kelvin units are measured on an absolute scale, and are often associated with the measurement of gas temperature, particularly important when calculating values using any of the gas laws.
4. Expansion refers to an increase in volume, and an increase in the amount of space between particles in a sample of matter. Compression is the opposite of expansion, referring to a decrease in volume and a decrease in the amount of space between particles in a sample of matter.

• Activity Questions:

1. a. T₁ = 50.0 ⁰C, V₁=2.000 cm ³ , D₁= 7.850 g/cm³
   b. T₂=90.0 ⁰C
   c. The volume of the nail increased by 0.001cm³ when the temperature was increased. This change cannot be seen in the image of the nail because it is so minor; however the particles in the sample can be seen to increase their speed.
   d. V₂= 2.001 cm³, D₂= 7.846 g/cm³
2. a. n/a
   b. T₂=23.0 ⁰C
   c. The volume of the nail decreased by 0.001cm ³. The particles in the sample can be seen to decrease their speed.
   d. V ₂= 1.999cm³, D₂= 7.854g/cm³
   e. As the temperature fluctuates throughout the year, it is important that the connectors be able to expand and compress as needed in order to support the bridge properly.
3. a. There is much more empty space between particles, and the particles in the liquid sample can flow more freely than the particles in the solid sample.
   b. Correct answer is “a temperature increase will cause the volume of water to increase.”
   c. The volume increases from 10.00mL to 10.20mL. The particles in the sample move faster when the temperature has been increased.
   d. D ₂ (at 90.0⁰C)= 0.965 g/mL
   e. D₂ (at 23.0⁰C) =0.998g/mL
   f. greater than 10.00mL, but less than 10.20mL
   g. In general, as the temperature of liquid water increases, the density decreases, and as the temperature of liquid water decreases, the density increases. This is an indirect relationship.
   h. Volume =103.6mL
4. a. The volume in the balloon will increase when temperature is increased and the volume will decrease when temperature is decreased; this is a direct relationship.
   b. The volume in the balloon will decrease when pressure is increased and the volume will increase when pressure is decreased; this is an indirect relationship.
   c. Increasing the pressure only.
   d. D₂ (at 2.00atm) = 0.357g/L
   e. D₂ (at 90.0⁰C) = 0.159g/L
   f. Yes!