Experiment 3.

Density Determination

LEARNING OBJECTIVES

The students will be able to learn that:

1. The density is an intensive property and it is independent of the amount of sample used.

2. The volume of an object can be determined by the volume of the water it can displace.

3. The density of a mixture is between the densities of the constituents forming the mixture.

BACKGROUND

Density is a physical property of a substance that is often useful part of its identification. Density of a substance is described as the mass of a unit volume and it is an intensive property. Intensive properties do NOT depend on the amount of the sample used. Density may be thought of as how heavy an object is for its size, or the ratio of an object’s mass to its volume.

The units of density of a solid object are g/cm3 and for the liquids are in g/mL. (1 cm3 ≈ 1 mL).

There are three parts to this experiment.

a. Density of the regularly shaped objects.

b. Density of the irregularly shaped objects (water displacement method). c. Density of a mixture

In these investigations, you will determine the density of several objects by measuring their mass and volume. The density of a sample usually varies inversely with temperature. The density of an object usually decreases with increasing temperature. Therefore, when reporting the density of a sample, you must report the temperature in the laboratory during the experiment; i.e. “the density of water is 0.997 g/mL at 25 oC”.

SAFETY INFORMATION

1. NO EATING or DRINKING IS ALLOWED IN CHEMISTRY LABORATORIES.

2. OBTAIN and WEAR EYE GOGGLES AT ALL TIME.

3. NOTIFY YOUR INSTRUCTOR IF YOU HAVE ANY QUESTIONS.

4. WASH YOUR HANDS BEFORE LEAVING THE LABORATORY.

MATERIALS

10-mL graduated cylinder, 100-mL graduated cylinder, centigram balance, metric ruler, rectangular or cubic shaped objects (PVC, Wood, Brass, Iron, Copper, Aluminum), marble chips, unknown salt solutions.

DRY LAB SIMULATION:

PRELAB QUESTIONSNAME:

1. Identify the formula for determining the density.

2. List the units for the variables found in the density formula.

3. Identify the formula for a rectangular solid (cuboid).

4. Look at the table of densities found on page 41 in the lab book. Based on the information provided predict if rubber will float.

5. Look at the table of densities found on page 41 in the lab book. Identify one material which will float.

PART A: DENSITY OF A REGULARLY SHAPED OBJECT

h

l

w

Figure 1: Determination of the volume of a cubic or rectangular shaped object

The volume of the object (cm3) = length (cm) × height (cm) × width (cm)Equation 2.

PROCEDURE:SAMPLE #:

1. Obtain a cubic/rectangular object from the box and record the sample number.

2. Weigh the object using a centigram balance.

3. Measure the length, the width, and the height of the object.

4. Calculate the volume of the object using the formula given in Equation 2.

5. Calculate the density of the object using Equation 1.

6. Repeat the experiment and take the average value of the density. This is needed to minimizeerror in the experiment.

NOTE: ALL MEASUREMENTS WILL HAVE TWO DIGITS AFTER THEIR DECIMAL POINTS.

9. Find the accepted density of the sample from the table provided below and calculate the percent error in your determination:

Table 1: Density of some common materials.

Accepted value  exp erimental value

Percent Error  | | 100 =

Accepted value