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# 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

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