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Experiment 2
This laboratory provides a bit of fun for the student; the student will use the equipment
in the locker to solve a puzzle. Each will be given unknowns of various kinds and asked to
find out the identities by taking suitable measurements. Thus, using precision, accuracy, and
significant figures in their measurements, each unknown can be identified. (Eureka!)
In the use of the balances, again remind students not to weigh directly on the pan, but
to use a container or weighing paper. In the case of the unknown metal, provide suitable
containers for their recovery. For the other unknowns, waste containers should be provided.
Nothing should be discarded into the sink.
Reading the volume in a graduated cylinder requires lining up of the eye with the
meniscus. Demonstrate the proper technique for doing this. It may be the student’s first
encounter with the Spectroline pipet filler. It would be best to go through the way it works,
particularly in the suction phase of its use. If the tip of the pipet is not immersed far enough
into the liquid to be pipetted, the force of the suction might cause the liquid to be drawn up
into the Spectra line pipet filler’s body; these liquids will cause the inside to deteriorate. In
addition, the liquids in the pipet filler will contaminate the next liquid to be pipetted, and so
this situation should be avoided.
NAME SECTION DATE
PARTNER GRADE
Experiment 2
PRE-LAB QUESTIONS
A. Safety concerns
1. Why do you not discard your solid or liquid samples into the sink? Where should you discard
these samples?
The samples may pollute the environment; also, they may stop-up the drain if they do not
dissolve. Samples should be disposed of in appropriately labeled waste containers.
2. Should you use your mouth when you pipet a liquid? Explain.
Never use your mouth to pipet a liquid. The liquid may be poisonous if swallowed or can
cause burns if any got into the mouth.
3. Why is it necessary to lubricate the end of the pipet before inserting into the pipet filler?
In order not to force, lubrication allows the glass to enter the opening without binding.
Forcing may break the glass.
B. Basic principles
1. Identify the following characteristics as either an intensive property or an extensive property.
Intensive
a. Melting point. ____________ _
Intensive
b. Color —————– Extensive
c. Volume _______________ ,
Extensive
d. Mass —————- Intensive
e. Density ______________ _
2. Cork stoppers float on water. Could you use the water displacement to determine the density
of the cork stopper? Explain.
The displacement method depends on the object being completely submerged. Since the
cork floats, not all of it is covered with water, so not all of the object would be accounted for,
and the method would not work.
3. Exactly 50.0 mL ofliquid has a mass of 40.30 g. What is its density? Show your work.
40.30 g150.0 mL = 0.806 g/mL
NAME SECTION DATE
PARTNER GRADE
Experiment 2
REPORT SHEET
Report all measurements and calculations to the correct number of significant figures.
A. Density of a regular-shaped object Trial! Trial 2
1 (wood block)
Unknown code number
20.8 20.8
1. Length cm cm
5.3 5.3
Width cm cm
4.4 4.4
Height cm cm
485 485
2. Volume (L x W x H) cm3
cm3
287.57 287.57
3. Mass g g
0.593 0.593
4. Density: (3)/(2) g/cm3 g/cm3
0.593
Average density of block g/cm3
B. Density of an irregular-shaped object Trial! Trial 2
2 (Al shot)
Unknown code number
5.232 6.702
5. Mass of metal sample g g
14.90 16.80
6. Initial volume of water mL mL
16.80 19.30
7. Final volume of water mL mL
1.90 2.50
8. Volume of metal: (7) – (6) mL mL
2.75 2.68
9. Density of metal: (5)/(8) g/mL g/mL
2.72
Average density of metal g/mL
Aluminum
10. Identity of unknown metal
C. Density of water Triall Trial 2
22.0 22.0
11. Temperature of water DC DC
26.264 26.257
12. Mass of 50-mL beaker g g
Volume of water 10.00 mL 10.00 mL
36.143 36.176
13. Mass of beaker and water g g
9.879 9.919
14. Mass of water: (13) – (12) g g
0.9879 0.9919
15. Density of water: (14)/ 10.00 mL g/mL g/mL
0.9899
16. Average density of water g/mL
0.998
Density found in literature g/mL
D. Density of unknown liquid Triall Trial 2
3 (Ethanol)
Unknown code number
22.0 22.0
17. Temperature of unknown liquid DC DC
26.810 26.810
18. Mass of 50-mL beaker g g
34.671 34.842
19. Mass of beaker and liquid g g
7.861 7.882
20. Mass ofliquid: (19) – (18) g g
Volume of liquid 10.00 mL 10.00 mL
0.7861 0.7882
21. Density ofliquid: (20)/10.00 mL g/mL g/mL
0.7872
Average density of unknown liquid g/mL
Ethanol
22. Identity of unknown liquid
POST -LAB QUESTIONS
1. When a student drew liquid into the volumetric pipet, air bubbles were trapped in the volumetric
‘pipet Would this give a density less than expected or greater than expected? Why?
The air bubbles occupy space, so it would appear that the metal pieces had a bigger
volume than there actually was. Since the mass did not change, only the volume (which appears
larger) “changed;” Thus, the density would be less than expected.
2. A student has a regular wooden block to work with for a density determination. Unknown to
the student is that the block has a hollow center. How will this affect the student’s determination
of the density?
The density would be less than it should be. The volume displaced assumes a completely
solid object. The mass of the hollow solid is less than the mass of a completely solid block of the
same volume.
3. Ethanol has a density of 0.791 g/cm3 at 20o
e. How many milliliters (mL) are needed to have
30.0 g of liquid? Show your work.
d=m/V
0.791 g/cm3 = 30.0 g/V
v = 30.0 g/O. 791 g/cm3 = 37.9 cm3 = 37.9 mL
