Name: ______________________
Density
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.
2. According to the drawings above, which state of matter is typically the most “dense”?
3. 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?
4. Define the vocabulary terms “expansion” and “compression” in relation to the behavior of the particles in a sample of matter.
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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?
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c. 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.
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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
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•
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.
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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?
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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.?
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