Density of Solids and Liquids

Honors Chemistry Lab

Objectives

The objectives of this laboratory are:

a)  To determine the density of Aluminum (applying the technique of water displacement) and to use it to determine the thickness of a piece of aluminum foil.

b)  To determine the volume of a regularly shaped solid via its measured dimensions.

c)  To determine the density of pure liquid water and pure liquid ethanol.

Background

Volume is the amount of space occupied by matter. Volume is an extensive property. An extensive property is one that is dependent on the amount of matter present. In other words, the greater the quantity of a substance, the larger the volume of that substance.

The volume of a liquid can be directly measured with specialized glassware, typically in units of milliliters (mL) or liters (L). Note that when measuring liquid volumes, it is important to read the graduated scale from the lowest point of the curved surface of the liquid, known as the liquid meniscus.

The volume of an irregular solid must be measured indirectly based on its shape. For regularly shaped solids, such as a cube, sphere, cylinder, or cone, the volume can be calculated from its measured dimensions (length, width, height, diameter) by using an appropriate equation.

For irregularly shaped solids, the volume can be indirectly determined via the volume of water (or any other liquid) that the solid displaces when it is immersed in the water (Archimedes Principle). The units for solid volumes are typically cubic centimeters (cm3) or cubic meters (m3). Note that 1 mL = 1 cm3.

Measuring the Volume of an Irregularly Shaped Solid

Volume water displaced = Final volume – Initial volume

Volume water displaced = Volume of solid

Density is defined as the mass per unit volume of a substance. Density is a physical property of matter. Physical properties can be measured without changing the chemical identity of the substance. Since pure substances have unique density values, measuring the density of a substance can help identify that substance. Density is also an intensive property. An intensive property is one that is independent of the amount of matter present. For example, the density of a gold coin and a gold statue are the same, even

though the gold statue consists of the greater quantity of gold. Density is determined by dividing the mass of a substance by its volume:

Density is commonly expressed in units of g/cm3 for solids, g/mL for liquids, and g/L for gases.

In Part A of this lab, the mass and volume of a sample of aluminum will be measured in order to determine its density.

In part B the experimental density will then be used in an applied problem to determine the thickness of a piece of aluminum foil.

In Part C the density of water and ethanol will be determined

Procedure

Safety

Be careful when adding the aluminum to your graduated cylinder, as the glass could be broken. Also, ethanol is flammable, so avoid using it near an open flame. Although pure ethanol is in alcoholic beverages, the ethanol you are using has been denatured. This means it is unsafe to drink. Don’t even think about it.

Materials and Equipment

10-mL graduated cylinder, 50 mL beaker, metric ruler, aluminum pellets, aluminum foil, electronic balance, ethanol, pipets

Part A: The Density of Aluminum

1)  Obtain a sample of aluminum pellets from your instructor. The pellets will be labeled 1-5.

2)  Using the electronic balance, determine the mass of each pellet. Record this in your data table.

3)  Pour about 5 mL of water into your 10-mL graduated cylinder. Precisely note this volume. Record it in your data table. (It should be to 2 decimal places)

4)  Carefully add one aluminum pellet at a time to the water, making sure not to lose any water to splashing. Also make sure that the pellets are all completely immersed in the water. Measure the new volume after each pellet has been added. Record this in your data table.

5)  When finished, retrieve and dry the aluminum pellets and return them to their bag.

Part B: The Thickness of Aluminum Foil

1)  Obtain a rectangular piece of aluminum foil.

2)  Use the ruler to measure the length and width of the piece of foil in cm.

3)  Fold the foil up into a small square and measure its mass using the electronic balance. Record this in your data section.

4)  When finished, return the foil, and meterstick.

Part C: The Density of the Liquid Water and Ethanol

Ethanol

1)  Using the electronic balance, obtain the mass of your clean, dry 10-mL graduated cylinder. Record this in your data section.

2)  Add approximately 5 mL of pure liquid ethanol to the 10-mL graduated cylinder. Use the pipet attached to the bottle of ethanol. Record the volume of ethanol used in your data section.

3)  Now obtain the mass of the cylinder and ethanol. Record this in your data section.

4)  Pour your ethanol down the drain.

5)  Rinse your graduated cylinder out with water. Be sure to dry the entire outside.

6)  Add approximately 5 mL of tap water to the 10 mL graduated cylinder. Record the volume of water used in your data section.

7)  Now obtain the mass of the cylinder and water. Record this in your data section.

Name ______Date ______Block ___

Data

Part A

Volume of Water in 10.00 mL graduated cylinder (mL)

Pellet # / 1 / 2 / 3 / 4 / 5
Mass (grams)
Volume (mL)
Pellet #1 Added
Pellet #2 Added
Pellet #3Added
Pellet #4 Added
Pellet #5 Added

Part B

Length of Aluminum Foil (cm)

Width of Aluminum Foil (cm)

Mass of Aluminum Foil (grams)

Part C

Mass of clean dry 10 mL graduated cylinder (grams)

Volume of Ethanol Added (mL)

Mass of Ethanol and cylinder (mL)

Volume of Water Added (mL)

Mass of Water and cylinder (mL)

Calculations – Complete on a separate sheet of paper.

Part A

1)  Calculate the volume of each aluminum pellet in cm3.

2)  Determine your experimental density of aluminum based on the total volume of aluminum and total mass of aluminum.

3)  Look up the Accepted value for the density of aluminum and calculate your percent error.

Part B

1)  Use your calculated (experimental) density of aluminum to determine the thickness of aluminum foil. (In millimeters)

Part C

1)  Determine the mass of ethanol used.

2)  Calculate the density of ethanol.

3)  Look up the Accepted value for the density of ethanol and calculate a percent error.

4)  Determine the mass of water used.

5)  Calculate the density of water.

6)  Look up the Accepted value for the density of water and calculate a percent error.

Questions – Complete in the space provided

Part A

1)  Explain why the density of aluminum is considered a physical property?

2)  Is aluminum a mixture or pure substance? Explain your reasoning.

Part B

No questions

Part C

1)  Propose reasons why the density of ethanol is different than the density of water.

Complete the following on the BACK of this sheet of paper.

Discussion of Theory -- What scientific principles allow this lab to be performed.

Discussion of Error -- Not human error. What can cause your results to be off. P.S. This lab does not have any experimental error.

Conclusion – Summarize your findings. What did you learn?

Directions for Turning In

1) Detach pages 5-8. 2) Staple your picture procedure in front of page 5. 3) Staple your calculations after page 8.

Reference

Adapted from:

Chemistry 10 Lab Manual. Santa Monica College. 12 Jan. 2005
<http://homepage.smc.edu/chem10/Experiments.html>.

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