Introduction:
Density is a physical property of a substance defined as the quantity of mass in a given unit of volume. Mathematically, Density = Mass/Volume. Units for density are usually g/mL or g/cm3. Density is an intensive property, that is, the density of a substance always has the same value regardless of the size of the sample. No matter what size sample of mercury you may have, the density is always 13.8 g/mL. To determine the density of a substance, you must measure both its mass and volume. Mass can be measured using an electronic balance either directly or indirectly. There are several methods to determine the volume of an object. A metric ruler is used to record the length, width, and height of a regular- shaped solid and these measurements are multiplied together to get the volume in cm3. For Irregular-shaped solids, the water displacement method is used; this is an indirect way of finding the volume of a solid. You will find the densities of several know substances using the methods discussed above. You will then compare these densities to the actual densities and determine your % error.
%
Error = Experimental value – Accepted value x 100
Accepted
value
Objectives:
1. Determine the density of several solids and liquids
2. Compare these values to the accepted densities
3. Calculate percent error of your team's data
Materials:
Balance, 100-mL graduated cylinder, 25 ml pipette and beaker
Honors: water, alcohol, copper (II) sulfate, and 7 metals
Academic: water, alcohol, copper (II) sulfate, and 4 metals
Procedure:
Solids
1. Measure and record the mass each metal sample.
2. Fill a 100-mL graduated cylinder about 2/3 full of tap water. Record the volume to the tenth place
3. Slide the metal sample carefully into the graduated cylinder. Record the volume of the water and stone to the tenth place.
4. Repeat steps 1-3 with each metal sample provided
Liquids
1. Mass and record an empty and dry beaker.
2. Obtain a 25 ml pipette and rinse it twice with tap water and once with distilled water.
3. Pipette 50 ml of distilled water into the massed beaker.
4. Mass the beaker again, with the water added.
5. Repeat steps 1-4 with each liquid sample provided
Data table:
Create two data
tables, one for the liquids and one for the solids. The data tables should
include a columns for sample, mass,
volume, experimental density, actual density and % error
Analysis:
1.
Calculate the densities of each sample by showing the formula and
calculation of the first sample for each data table. (Meaning one liquid sample
and one solid sample)
2.
Using the Handbook of chemistry and physics, look up the density values
of each sample and record in the data table
3.
Calculate your team's percent error using the formula in the background
section of the lab sheet.
Questions:
1.
What is the definition of density?
2.
Describe how the volumes of the metal samples were determined indirectly.
3.
Describe how the mass of the liquid samples were determined indirectly.
4.
Why was a pipette used to determine the volume of the liquids instead of
another type of glassware?
5.
What does the percent error of measurement describe?
Conclusion:
Remember to restate your objectives in the first paragraph
and include your results in describing the procedure. The last paragraph should
include you opinion about the effectiveness of the lab procedure meeting the
objectives.