PHYSICAL PROPERTIES
Objectives: To observe and make generalizations about the melting point, boiling point,
solubility, electrical conductivity and volatility (odor) of different classes of substances.
Introduction: There are four general classes of substances: ionic, molecular, network (including
macromolecules) and metallic. Ionic compounds are substances that are held together by the
attraction of the oppositely charged ions that compose the compound. The strength of the ionic
force depends on the charge and the size of the ions. Molecular substances are those substances
whose atoms are held together by covalent bonds (the intramolecular forces) while the individual
molecules are held together by various intermolecular forces (dipole, London dispersion forces,
and "hydrogen bonds" ). The physical properties of molecular substances depend on which of
these intermolecular forces are present and their relative strength. Most of the nonmetallic
elements are molecular (carbon in the forms of diamond and graphite, and silicon are networks).
Networks and macromolecules are substances that contain very large numbers of atoms held
together by covalent bonds and the intermolecular and the intramolecular forces may be involved
in determining their physical properties. Metallic substances are the pure metallic elements or
alloys of those elements which are held together by the "metal bond" involving the attraction
between positive metal ions and a mobile pool of electrons.
Procedure:
Melting Point: Arrange the substances listed below in the indicated pattern around the outer edge
of a aluminum pan or stainless steel spotting plate. The number of wells may be less than the
number of solid unknowns so you may need to use a somewhat different pattern.
zinc
zinc chloride
magnesium oxide
silicon Dioxide
para-dichlorobenzene
tin
potassium iodide
sulfur
sucrose
Use very small amounts of each substance. Heat the metal pan strongly on a hot plate for about
five minutes. Record the order in which the substances melt. If a substance does not melt after
heating strongly for a minute or two, record it as nonmelting. Let the pan cool to room
temperature before handling.
PhyproT.rtf NCSSM 2001
1
Volatility: A substance which is volatile has a measurable or detectable vapor pressure. It may
or may not have an odor, however if it does have a strong odor, it probably does have a
significant vapor pressure. A substance which is volatile has weak intermolecular forces of
attraction. Carefully smell samples of potassium iodide, zinc, sucrose, sand, and
p-dichlorobenzene by waving some of the vapor present towards you. Do not smell them
directly. Record whether the odor is detected and the relative strength of the odor.
Boiling Point: The temperature at which the vapor pressure of a liquid is equal to the external
atmospheric pressure. A normal boiling point is the temperature at which the vapor pressure is
equal to 1 atm. Place about 2 mL of each of the following liquids in separate test tubes: ethanol,
1-propanol, and hexane. Add a boiling chip each tube. Place the tubes in a beaker of water on a
hotplate. Heat the water and watch when each sample boils. Measure the temperature of the
boiling liquid by placing a thermometer directly into the boiling liquid in the test tube. Wipe the
thermometer dry between measurement of the boiling points of the different liquids. Remove
each tube from the water bath after you have measured the boiling point. Empty any remaining
liquid into the waste bottle in the hood.
Solubility:
Solids: The solubility is the maximum amount of solute that will dissolve in a given amount of
solvent at a specific temperature. Place a few grains of sucrose in two clean DRY test tubes and
add 5 mL of water to tube one and 5 mL of hexane to the second tube. Stir each tube thoroughly
with a stirring rod and record the relative solubility in each solvent. Empty the tubes in the waste
bottle in the hood. Repeat these tests with potassium iodide and p-dichlorobenzene.
Liquids: Place about 2 mL of each of the two liquids in the combinations below in a small
testtube. The test tubes for d and e must be dry. Stir thoroughly and record their relative
solubilities. Empty the tubes in the waste bottles under the hood.
a.
b.
c.
d.
e.
f.
g.
h.
Water/ ethanol
Water/ 1-propanol
Water/ 1-butanol
Water/ 1-pentanol
Water/ hexane
Water/ acetone
Ethanol/hexane
Hexane/ cyclohexane
Electrical Conductivity: For a substance to conduct electricity, either ions must be able to move
through the system or electrons must be able to flow. You will test the electrical conductivity of
the substances below using a conductivity tester either directly on the substance or on the sample
in the specially prepared tubes. The molten compound will be done as a demonstration.
PhyproT.rtf NCSSM 2001
2
a. copper
c. sulfur
e. solid potassium iodide
g. distilled water
i. NaCl in ethanol
k. ethanol in water
m. cyclohexane in hexane
b.
d.
f.
h.
j.
l.
mercury
graphite
molten potassium iodide(demo)
NaCl in Water
hexane
silicon dioxide (sand)
PhyproT.rtf NCSSM 2001
3
NAME____________________________
LAB PARTNER____________________________
COURSE___________Period________
DATE____________________________
PHYSICAL PROPERTIES
Data:
1.
Melting Point
Substance
Melts
(Yes/No)
Melting Pt.
from CRC
Bond Type
Classification
Ranking of
Melting
Zinc
Potassium Iodide
Tin
Magnesium Oxide
Sulfur
Silicon Dioxide(sand)
Sucrose
Zinc Chloride
Paradichlorobenzene
2.
Volatility
Substance
Potassium Iodide
Zinc
Sucrose
Silicon dioxide(sand)
p-dichlorobenzene
3.
Odor(Yes/No)
Relative Odor
Bond Type
Classification
Boiling Point
Substance
Ethanol (C2H5OH)
1-Propanol (C3H7OH)
Hexane (C6H14)
Boiling Point(C)
PhyproT.rtf NCSSM 2001
4
Classification
Polar/Nonpolar
4.
Solubility of Solids:
Compound
Sucrose
Potassium Iodide
p-dichlorobenzene
Solvents
Water
Hexane
Classification
Polar/Nonpolar
Liquids
Relative Solubility
Classification
Polar/Nonpolar
Water/ethanol
Water/ 1-propanol
Water/ 1-butanol
Water/ 1-pentanol
Water/ hexane
Water/ acetone
Ethanol/ hexane
Hexane/ cyclohexane
5.
Electrical Conductivity
Substance
Copper Solid
Mercury Liquid
Sulfur Solid
Graphite
Molten Potassium Iodide
Distilled Water
Sodium Chloride in Water
Sodium Chloride in Ethanol
Hexane
Ethanol in Water
Silicon dioxide(sand)
Cyclohexane in Hexane
Electrical Conductivity
PhyproT.rtf NCSSM 2001
5
Bond Type
Classification
6.
What is the general order of the melting points of the different classes of compounds?
7.
What general statements can be made about the volatility of the different classes of
substances?
8.
What general statements can be made about the boiling points of polar and nonpolar
molecular compounds with respect to their molar masses?
9.
a) What general statements can be made about the solubility of ionic, polar molecular and
nonpolar molecular compounds in polar and nonpolar solvents?
b) What general statement can be made about the relative solubility of the series of
alcohols you investigated?
10.
What types of substances:
a) conduct electricity as a solid?
b) conduct electricity in the molten state?
c) conduct electricity as an aqueous solution?
d) do not conduct electricity?
PhyproT.rtf NCSSM 2001
6