Experiment 3.
Density Determination
LEARNING OBJECTIVES
The students will be able to learn that:
- The density is an intensive property and it is independent of the amount of sample
- The volume of an object can be determined by the volume of the water it can
- The density of a mixture is between the densities of the constituents forming the
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.
| mass | m g( ) | ||
| Density | ” d = | Equation 1. | |
| volume | V (mL) |
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.
- Density of the regularly shaped
- 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
- NO EATING or DRINKING IS ALLOWED IN CHEMISTRY
- OBTAIN and WEAR EYE GOGGLES AT ALL
- NOTIFY YOUR INSTRUCTOR IF YOU HAVE ANY
- WASH YOUR HANDS BEFORE LEAVING THE
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: http://phet.colorado.edu/sims/density–and–buoyancy/density_en.html
PRELAB QUESTIONS NAME:
- Identify the formula for determining the
- List the units for the variables found in the density
- Identify the formula for a rectangular solid (cuboid).
- Look at the table of densities found on page 41 in the lab book. Based on the information provided predict if rubber will
- 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
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 #:
- Obtain a cubic/rectangular object from the box and record the sample
- Weigh the object using a centigram balance.
- Measure the length, the width, and the height of the
- Calculate the volume of the object using the formula given in Equation
- Calculate the density of the object using Equation
- 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.
| DATE: | NAME: | |
| DATA SHEET FOR PART A. | Trial 1 | Trial 2 |
| 1. Measure and record the temperature. | oC | oC. |
| 2. Mass of the object. | grams. | grams. |
| 3. Length of the object |
cm. |
cm. |
| 4. Width of the object |
cm. |
cm. |
| 5. Height of the object |
cm. |
cm. |
| 6. Volume of the object: V = L × H × W |
cm3. |
cm. |
| 7. Density of the object (line (2) / line (6)) | g/cm3 | g/cm3. |
| 8. The average density of the object: |
g/cm3 at oC. |
|
- Find the accepted density of the sample from the table provided below and calculate the percent error in your determination:
| MATERIAL | Density (g/cm3) at 20oC |
| Acrylic | 1.18 |
| Aluminum | 2.73 |
| Brass | 8.55 |
| Wood | 0.40 |
| Copper | 8.90 |
| Gold | 19.3 |
| Iron | 7.68 |
| Lead | 11.4 |
| Marble Chips | 2.70 |
| Nylon | 1.30 |
| PVC | 1.41 |
| Rubber | 1.20 |
| Steel | 7.85 |
| Water | 0.99 |
Table 1: Density of some common materials.
Accepted value exp erimental value
Percent Error | | 100 =
Accepted value
Part B: Determination of the density of an irregular shaped objects
For each trial, pour about 20 – 30 mL of water into a 50-mL graduated cylinder. Accurately record the volume of water to the nearest 0.1 mL. Dry the outside of the cylinder with a paper towel. Obtain the mass of the graduated cylinder and water with your balance and record the mass to the nearest 0.01
- Weigh 20 marble chips (for the first trial) and 30 marble chips (for the second trial). Carefully drop the chips in the graduated cylinder and gently tap out any air bubbles. Record the new volume level in the graduated cylinder to the nearest 0.1 mL. Calculate the density of the marble chips to the nearest 0.1 g/mL.
Figure 2: Reading the volumes from graduated cylinders.
Note: Segregate the large marble chips and do not use them.
DATE: NAME:
DATA SHEET FOR PART B.
|
Trial 1 (20 chips) Trial 2 (30 chips)
- Density of the marble chips: (Line 1) / Line 4) g/mL g/mL Calculate the average density of the marble chips (show your work): g/mL.
- The accepted density of the sample (marble chips) is 2.70 g/mL. Calculate the percent error in your determination:
Accepted value exp erimental value = %
Percent Error | | 100
accepted value
PART C: DETERMINATION OF DENSITY OF SALT-WATER MIXTURE
Obtain an unknown saline solution from your instructor. Record the number of the unknown sample .
PROCEDURE and DATA SHEET FOR PART C. Trial 1 Trial 2
- Weigh an empty 10-mL graduated cylinder: g g
- Fill the graduated cylinder with the unknown sample to exactly 10-mL V = 10.00 mL.
- Weigh the 10-mL graduated cylinder and the sample again: g g
- Mass of the sample (Line 3) – (Line 1): g g
- Density of the unknown sample: (Line 4) / (Line 2) g/mL. g/mL
- The average density of the unknown sample: g/mL
- Determine the percent composition of your sample from the chart below using the average density of the two trials:
| 8. Measure and record the temperature. | oC. |
| Salt (%) | Density (20oC) |
| (Pure water) 0.0 | 0.998 g/mL |
| 5.0 | 1.036 g/mL |
| 10.0 | 1.074 g/mL |
| 15.0 | 1.112 g/mL |
| 20.0 | 1.152 g/mL |
| 25.0 | 1.193 g/mL |
| (Pure salt) 100.0 | 2.165 g/mL |
- The unknown sample has a density of g/mL. The concentration of the salt is %.
POST-LABORATORY QUESTIONS NAME:
(Observe the significant figures rules in your calculations).
- What is the density of a piece of concrete that has a mass of 8.76 g and a volume of 3.07 cm3?
- Cobalt has a density of 8.90 g/mL. What volume would 17.8 g of cobalt occupy?
- Limestone has a density of 2.72 g/cm3. What is the mass of 24.9 cm3 of limestone?
- A rectangular object has the following dimensions: length 2.00 cm, height 3.00 cm and the width
1.50 cm. It weight is 34.26 grams. What is the density of the object?
- A cylindrical metallic piece weighs 20.00 grams. When it is dropped into a graduated cylinder, the volume of water rises from 50.0 mL to 55.5 mL. What is the density of the piece?
- The density of alcohol is 0.80 g/mL and that of the water is 1.00 g/mL. What is the density of a mixture prepared by mixing 50.0 mL of water and 50.0 mL of alcohol assuming that the volumes are additive?
7a. The density of sugar solutions at various concentrations is tabulated below. Using the chart construct the graph density (y–axis) versus % weight (x–axis). Note: Must use Excel® to graph the below data.
| Density (g/mL) | % by weight (w/v) |
| 0.998 | 0 |
| 1.018 | 5 |
| 1.038 | 10 |
| 1.059 | 15 |
| 1.081 | 20 |
| 1.104 | 25 |
| 1.127 | 30 |
| 1.151 | 35 |
| 1.176 | 40 |
7b. A student determines the density of degassed (flat soda). The density is found to be 1.040 g/ mL. Using the graph you constructed in 7a, determine the sugar content in a 12-oz can of Sprite®. (12 fl oz can equals 335 mL). (Hint: % weight by volume is the mass of sugar in 100 mL of drink,
e.g. if the density is 1.018 g/mL there are 5 grams of sugar in 100 mL of soda).
