StudentGuiders

# CHEM 101-Introductory Chemistry I-Lab 1 - Density

**Density**

Purpose:

To practice measuring techniques and graphing; to become familiar with density measurements and calculations.

Introduction:

In this lab, we will measure the density of several samples. The density of an object is defined as the ratio of its mass to its volume. We write this mathematically by using the equations:

or

For an example of density, consider the following example: Imagine a brick that is made of Styrofoam. Imagine a second brick that is made of lead. Note that even though the bricks take up the same amount of space - that is, they have the same volume - there is a major difference in their mass or weight. We would say that the lead is more dense. It has more mass in the same volume.

It is important to note that water has a density of 1.0 g/mL. Objects that have a density less than water, that is, less than 1 g/mL, will float on the surface of the water. Those that have a density greater than 1 g/mL will sink. Consider our two bricks again. The brick of Styrofoam will float if we toss it into water. The lead will quickly sink.

Modern ship manufacturers make use of density when designing the ships they build. They use materials that are more dense than water but shape the materials so that they take up enough space to float. Although the ships weigh several thousand tons, that weight takes up a lot of space. Overall, the ship has a density less than that of water and it floats.

Two factors have an effect on the density of water:

1) Temperature will have a small effect on the density. For this lab, we will ignore any temperature effects. They are negligible.

2) If other compounds are dissolved in the water, it will be more dense.

Procedure:

A) Wood Block

Obtain a wooden block. Use the electronic balance to obtain its mass in grams. Record this value in the data table. Use a ruler and measure each dimension of the block. Find the volume of the block by multiplying the three lengths together. Note that this volume will be in cubic centimeters. A cubic centimeter and a milliliter represent the same volume.

cm x cm x cm = cm3 = mL

Compute the density by dividing the mass by the volume.

B) Irregular solid

Obtain an irregular solid. We will use a large bolt as our solid for this part of the experiment. Find its mass using the electronic balance.

Since it is irregular, finding the volume by using the rules of geometry would be very difficult. To find the volume, we will use a technique called water displacement. Fill a 100 mL PLASTIC graduated cylinder to about 40 mL with tap water. Record the exact volume of the water. Tilt the cylinder slightly and let the metal bolt slide in. Now record the volume of the water and the bolt. If you subtract the first volume from the second, you will have the volume of the bolt. Now find the density by dividing the mass by the volume.

C) Density of water

Using the analytical balance weigh a clean, dry 100 mL beaker. Record this mass.

Using a pipet, add 10.00 mL of tap water to the beaker and reweigh.

Calculate the density of water.

D) Density of unknown solution

You are repeating part C for an unknown liquid.

Using the analytical balance weigh a clean, dry 100 mL beaker. Record this mass.

Using a pipet, add 10.00 mL of an unknown liquid to the beaker and reweigh.

Calculate the density of the unknown liquid.

E) Thickness of aluminum foil

In this part of the experiment you will be required to determine the thickness of a piece of aluminum foil. The density of aluminum is 2.70 g/mL or 2.70 g/ cm3. The thickness is too small to measure with our instruments. We will measure the mass, calculate the volume using the density, and then calculate the thickness.

Measure and record the mass of the rectangular piece of aluminum foil. Measure and record the length and width of the aluminum foil. Calculate the volume of the foil using the density of aluminum and the mass of your sample.

Calculate the thickness of foil using this volume and the length and width of your sample.

Remember from geometry that the volume of a rectangular solid can be expressed by this equation:

Volume = length x width x height

In our case today, we will treat the thickness as the height, so that the expression becomes

Volume = length x width x thickness

And then

NAME _______Haoxing Shi________________________

DENSITY LAB SHEET

A) Wood Block

Mass of block _____2.307________ g

Length _____5.05_________ cm

Width _____1.00_______ _____ cm

Height ___ _____1.15_________ cm

Volume _________ 5.808 _____ cm3

Density _____ 0.397_________ g/cm3

B) Irregular solid

Mass ____22.234____ g

Volume of water _____50.5 ____ mL

Volume of water and bolt _____57.0_____ mL

Volume of bolt ___6.5_______ mL

Density of bolt _____3.421_____ g/mL

C) Density of water (one shot)

Mass of beaker _____57.333________ g

Mass with 10 mL _____67.110________ g

Mass of water ______ 9.777 _______ g

Volume of water ____10.00__________ mL

Density of water _______ 0.978 _______ g/mL

D) Density of an unknown solution (one shot)

Mass of beaker _____63.789_________ g

Mass with 10 mL _____72.154_________ g

Mass of liquid _____8.365___ ______ g

Volume of liquid _____10.00_________ mL

Density of liquid ___0.837______ _____ g/mL

E) Thickness of aluminum foil

Mass of the foil _____ 0.557________ g

Length of the foil _______9.85________cm

Width of the foil ______10.10________cm

Volume of the foil ____ ____0.947____ cm3 (or mL)

Thickness of the foil ______ 0.009_______ cm