Simulation: Density FOR THE TEACHER 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. • •
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Answers to the student activity: Pre-lab Questions: o 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. o 2. Solid o 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. o 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: o 1.a. T 1 = 50.0 ⁰C, V 1 =2.000 cm3 , D 1 = 7.850 g/cm3 b. T 2 =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. V 2 = 2.001 cm3, D 2 = 7.846 g/cm3 2.a n/a b. T 2 =23.0 ⁰C c. The volume of the nail decreased by 0.001cm3. The particles in the sample can be seen to decrease their speed. d. V 2 = 1.999cm3, D 2 = 7.854g/cm3
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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. D 2 (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. D 2 (at 2.00atm) = 0.357g/L e. D 2 (at 90.0⁰C) = 0.159g/L f. Yes!
FOR THE STUDENT Student Activity Sheet: Density Lesson Background Density is the mass of a substance per unit of volume. In this investigation you will interact with several different samples of matter, and examine how manipulating variables can affect the density of these samples. The formula for calculating density is: Density = mass volume Common unit of measurement for density include: g/ml, g/cm3 and g/L. Prelab Questions 1. In the squares below, draw how you think particles are arranged in the three states of matter: solid, liquid and gas. Use circles to represent the particles and label each box with the state it represents.
According to the drawings above, which state of matter is typically the most “dense”? 2. a. Define temperature. b. What is the difference between the Celsius and Kelvin temperature scales? Is there a situation where one unit should be used rather that the other? 3. Define the vocabulary terms “expansion” and “compression” in relation to the behavior of the particles in a sample of matter. Procedure Visit http://www.teachchemistry.org/density. Make sure that you have the simulation set to “solid” to begin. You should see a picture of a nail on your screen.
1. a. Record the initial values for temperature, volume and density in the table below (be sure to include the proper units):
T1 =
T2 =
V1 =
V2 =
D1 =
D2 =
b. Next, increase the temperature of the nail. Record the final temperature value (T 2 ) in the data table. c. Briefly explain how the increase in temperature affected the volume of the nail. Could you see this change in the image of the nail? d. Record the final volume (V 2 ) for the nail in the data table. Using the mass value shown on the screen for the nail, and the V 2 value, calculate the final density for the nail. (Show your calculations below): Use the “calculate” button to check your answer. 2. a. Press the “reset” symbol in the top corner of the screen. The initial values, shown in the table below should appear. T 1 = 50.0 ⁰C
T2 =
V 1 = 2.000 cm3
V2 =
D1 = 7.850g/cm3
D2 =
b. Next, decrease the temperature of the nail. Record the final temperature value (T 2 ) in the data table. c. How was the volume of the nail affected by the temperature decrease? Considering the particles of the nail, what is their response to this temperature change? d. Record the final volume (V 2 ) for the nail in the data table. Using the mass value shown on the screen for the nail, and the V 2 value, calculate the final density for the nail. (Show your calculations below): Use the “calculate” button to check your answer. e. Bridges often contain flexible connections in the middle. Based on what you’ve observed about how solids act when they are heated and cooled, why do you think they put flexible connectors in the road on a bridge? Change the simulation to “liquid” by clicking the option in the top left corner of the screen. You should now see a picture of water contained in a graduated cylinder on your screen.
3. a. Describe the most immediate difference you see at the particle level in the liquid simulation compared to the solid? b. Before changing the temperature value for the water sample, make a prediction by choosing one of the following statements as correct (it is okay if it turns out to be incorrect!): • • •
A temperature increase will cause the volume of the water to increase A temperature increase will cause the volume of the water to decrease A temperature increase will not affect the volume of the water
c. Now increase the initial temperature value from 50⁰C to 90⁰C. What happens to the volume of the water in the graduated cylinder, and what change can you see at the particle level? d. Using the mass value of the water, 9.88g, and the new value for the V 2 of water at 90⁰C shown on your screen, calculate the density value for this sample of hot water. (Show your calculations below): Use the “calculate” button to check your answer. e. Now reduce the temperature value of water to 23.0⁰C. Using the V 2 for the water, calculate the density of the room temperature sample of water. (Show your calculations below): Use the “calculate” button to check your answer.
f. If you heated the 9.88g sample of water to 70⁰C, what volume would you predict for the sample to occupy? How did you determine this? g. In one sentence, make a statement that describes the relationship between temperature change and the density of liquid water. h. If you were given a 100.0gram sample of water at 90⁰C, what volume would you expect the sample to occupy? (Show your calculations below): Change the simulation to “gas” by clicking the option in the top left corner of the screen. You should now see a picture of a helium balloon on your screen.
4. a. When temperature is changed, the pressure value is held constant at 1.00atm. How does volume respond to an increase in temperature? A decrease in temperature? b. When pressure is changed, the temperature value is held constant at 50.0⁰C. How does volume respond to an increase in pressure? A decrease in pressure? c. Based on your answers to the previous two questions, which of the following choices will result in an increase in the density of the helium balloon? Increasing the pressure only OR
Increasing the temperature only d. Calculate the density value for the helium balloon when the pressure value is increased to 2.00atm; use the V 2 value on the screen for the volume. (Show your calculations below): Use the “calculate” button to check your answer. e. Calculate the density value for the helium balloon with the temperature value increased to 90.0⁰C; use the V 2 value on the screen for the volume. (Show your calculations below): Use the “calculate” button to check your answer. f. Do the values that you calculated for density in parts d. and e. above support your answer to the question in part c.?
