Mass, Volume, and Density | Semester 1, Unit 2

LAB 2: MASS, VOLUME, AND DENSITY NOTE TO STUDENTS: This is a dry lab. You are only expected to perform the portions of this lab that do not require you to use laboratory equipment or supplies. WhenWITH appropriate, EXTENSION sample data may be supplied in the lab’s data tables to help you answer the questions.

Goals Table 2.1

1. Determine volumes of several objects Shape Formula Symbols from their linear dimensions and by displacement V = volume 2. Determine the density of several Rectangular l = length materials V = lwh Solid w = width h = height Materials and Equipment

50 mL graduated cylinder V = volume 150 mL beaker 2 π = 3.14… Aluminum bar, rectangular V = πr l Cylinder or r = radius Digital scale ¼πd2l Goggles d = diameter Polyethylene (PE) rod l = length Ruler Steel (iron) bolt water does not tend to cling to plastic Tape measure surfaces, there is little meniscus, and therefore no need to adjust for it. Materials Not Included In this experiment, we will put water in a graduated cylinder and then place Sodium chloride (table salt) an object in the cylinder. There must be Stirring utensil enough water to cover the object. The Water object will push aside, or displace, the water. If the object is submerged, the volume of Introduction the water displaced (pushed aside) is equal to the volume of the object and the rise in The volume of an object is the the water level will also equal the volume of amount of space it occupies. We often use the object. units of length to express volume. Objects There is a legend about Archimedes’ are three-dimensional (have length, width, discovery of displacement. The king and height), and the volume is often suspected that his crown was gold-plated expressed in cubic units. Two equations for silver rather than pure gold. Archimedes calculating the volume of regular-shaped needed to find the volume of the crown objects are given in Table 2.1. without damaging it. One day, he noticed Liquids are often measured in liters. In that the water rose when he stepped into this lab we will find the volume of liquids his bathtub. He was so excited to discover by using a plastic graduated cylinder. Your displacement that he immediately jumped lesson probably mentions a meniscus out of his tub and ran down the street (curve on the surface of the liquid). Since yelling “eureka” (“I have found it”). Nothing is said about his state of modesty. Copyright © 2017 Quality Science Labs, LLC 1 pe Learning Cheistry Labs

Density is defined as mass per unit of 5. Similar to what you did in Procedure volume. Remember, per means “divided by.” step 4, find the volumes of all the other The equation for density is: objects including the bolt. Does the PE rod float? How can you find the volume (Equation 2.1) __m of it by this method? Record your data ρ= V in Table 2.2. where ρ is the density, m the mass, and V the volume. This can be rearranged to give Part 2: The Density of Liquids an equation to find mass: 6. Measure the mass of the graduated (Equation 2.2) m = ρV cylinder using the digital scale. Carefully fill the graduated cylinder with exactly Procedure 50 mL of water and measure the mass Part 1: The Density of Solids of the cylinder and the water. Find the mass of the water by subtraction and 1. Use the digital scale to mass (weigh) the record this in Table 2.3 in the Questions aluminum bar, PE rod, and steel bolt. To section. do this, turn the scale on and make sure the mode is in grams and the display 7. Put about 75 mL of water into a 150 mL reads zero. Push the “M” or “Mode” beaker. Add about 5 cm3 (roughly one button to set the scale in “Grams” and teaspoon) of sodium chloride (table salt) the “T”, “Tear”, or “Zero” button to zero to the water. Stir the solution. Keep the scale so it reads all zeros. One at a adding salt and stirring until no more time, carefully put each object on the salt will dissolve in the water. You now scale and record the measurements in have a saturated salt solution. Table 2.2. 8. Use the method from Procedure step 2. Use the ruler to measure the dimensions 6 to find the mass of 50 mL of the salt of the aluminum bar and the PE rod. solution. Record this in Table 2.3. Estimate your measurements to the nearest tenth of a centimeter. Record Note: You have been calculating the density of solid the data in Table 2.2. materials, but fluids (liquids and gases) also have densities. The density of air varies with temperature, Note: Do not measure the dimensions of the bolt, as it humidity, and pressure, but it is approximately 1.0 kg/ is irregular in shape. m3. One interesting thing about air: dry air is denser than humid air. This is because a molecule of water has 3. Calculate and record the volumes of less mass than the average mass of an air molecule. these objects in cubic centimeters (cm3). 9. Measure the length, width, and height 4. We will also use the displacement of the room in which you are. Do this in method to find the volumes of all the meters and record the measurements in objects. Pour exactly 25 mL of water the space provided at the end of this lab, into the graduated cylinder. Tip the in Questions 8-10. cylinder (do not spill the water) and slide the aluminum bar into the graduated 10. Calculate the volume of the room. cylinder. Note the level of the water. The increase in volume in the cylinder 11. Using the approximate density of air, is due to the volume of the aluminum calculate the mass of air in this room. bar. Find the volume of the bar by subtraction and record this in Table 2.2. 12. Does the mass of air in this room surprise you? Explain. 2 Copyright © 2017 Quality Science Labs, LLC Mass, Volume, and Density

LAB 2 Questions for Mass, Volume, and Density

Table 2.2, The density of solids. Dimensions, Calculated Displacement Density, Material Mass, g cm Vol., cm3 Vol., mL g/mL Aluminum length = 9.7 39 width = 1.6 40 - 25 = 15 (bar) height = 1.0

diameter = 1.7 48 - 25 = 23 PE (rod) 21 length = 10.5

Iron(bolt) 39 XXX XXX 31.9 - 25 = 6.9

Note: Vol. = volume. Since the bolt has an irregular shape, find its volume by displacement only. 1. Calculate the volumes of the samples used in Procedure step 2. Record the calculated volumes in Table 2.2. Why could we not find the volume of the bolt by this method?

2. How did you find the volume of the PE rod using the displacement method? Note: 1 cm3 = 1 mL.

Because PE floats, push the rod under the water with a very small object, such as a pin, and volume of the pin is negligible and can be ignored.

3. Except for the bolt, note the difference between the calculated volumes and the volume found by the displacement method. Which method is more accurate? Why?

4. Use the volumes found by displacement to calculate the densities of the objects. Record your data in Table 2.2.

5. The accepted values for density are: aluminum = 2.71 g/cm3; PE = about 0.925 g/cm3; and iron = 7.87 g/cm3. Compare your values from Question 4 with these. How do they compare? Why are they different? Note: the density of different kinds of PE and PVC vary because of the difference in the arrangements of their molecules.

Table 2.3, The density of liquids Liquid Volume, mL Mass, g Density, g/mL

Water 50 77 - 27 = 50 Saturated Salt Solution 50 83 - 27 = 56

6. Calculate the densities of the liquids in Table 2.3. The accepted density of water is 1 g/ cm3. How do your results compare? Remember that 1 cm3 = 1 mL.

7. How does the density of water compare with the density of the saturated salt solution? Is this what you would have predicted?

8. Length of room ______4.02 m

9. Width of room ______3.37 m

10. Height of room ______2.35 m

11. Volume of room ______m3

12. Mass of air in room ______kg

13. Are you surprised by the mass of air in the room? Explain.