July12,2014

1. MELTING POINT
DETERMINATION
EXPERIMENT#8
DIAZ, HOVELYN LOU MARTINEZ, MA. CZARINA
ESTEBAN, REYNAN JAMES SANOTA, MARIELA
GREGORIO, KRYSTAL JANE

2. INTRODUCTION
A melting point can be used to identify a substance and to
get an indication of its purity. The melting point of a solid is
the temperature at which the solid exists in equilibrium with
its liquid state under an external pressure of one
atmosphere. Both the melting point range (the interval
between the beginning of liquefaction and complete
liquefaction) and the temperature of complete
liquefaction are valuable indicators of the purity of the
solid compound. A pure crystalline organic compound
usually possesses a sharp melting point and it melts
completely over a narrow temperature range.

3. PROCEDURE
Prepare 3 melting point capillary tubes by
heating the middle portion of the capillary
tube (1mm diameter) and when soft
enough, pull in opposite directions to
completely seal and separate the two. Test
the tube if completely sealed by blowing air
on the open end, and feeling with fingers if
air comes out from the sealed end, it should
be heated further to completely seal it.

4. PROCEDURE
Introduce powdered samples of acetanilide,
benzoic acid and salicylic acid into 3 separate
prepared capillary by putting a small amount
of sample (about 3-4 mm diameter) on a piece
of clean dry paper and pushing the open end
of the capillary tube into the sample to scoop it
up. The column of solid should not be more
than 1cm, in the tube length and it should be
tightly packed.

7. PROCEDURE
Prepare the set-up for melting point
determination

9. PROCEDURE
Fasten the capillary tube containing
acetanilide to the thermometer with string
or a rubber bond so that the sample is close
to and on a level with the center bulb of the
thermometer bulb. Attach the thermometer
in its place in the set-up where its bulb and
the capillary tube (with sample) is centered
in the beaker and submerged in the oil.

10. PROCEDURE
Heat the oil bath with a moderate
flame. Then gradually increase the
size of the flame so as to cause a
rise in temperature of 1 or 2 per
minute. Stir the bath continuously
to have a uniform heating.

11. PROCEDURE
RECORD:
a. The temperature at which melting begins and
b. The temperature when the entire 1cm
powdered sample in the capillary tube is
completely melted
Repeat the same procedure by using benzoic and
salicylic acid

13. DATA AND RESULTS
COMPOUND INITIAL TEMPERATURE FINAL TEMPERATURE
ACETANILIDE 105C 114C
BENZOIC ACID 110C 122C
SALICYLIC ACID 140C 150C

14. COMPOUND MELTING POINT
ACETANILIDE 114.3 °C
BENZOIC ACID 121-123°C
SALICYLIC ACID 159°C

15. QUESTIONS
1. What are the bonding forces that hold together the molecules in a
crystal? Give examples of compounds with such types of bonding forces.
 Intermolecular forces hold its molecules together such as Van der Waals forces, Ionic
bonding, Covalent bonding, Hydrogen bonding and Metallic forces.
 Examples:
I2, P8 and solid SO2 =Van der Waals forces. Weakly held and easily broken with low melting
points
NaCl, MgO, CaCo= Ionic forces composed of the electrostatic attractions of anions and
cations. Hard, brittle poor electrical conductors.
SiO = Covalent bonded crystal forming quartz and diamond crystals. Hard, poor conductors
of heat and electricity and have high melting points
All of the metallic elements: Ag, Mg, Fe Cu, etc= Metallic bonding positive ions surrounded by
delocalized valance electrons. Conduct heat and electricity well, have low to high melting
points and can be soft or hard.

16. QUESTIONS
2. What is the effect of an impurity on the melting
point of a substance?
 They cause the melting point to turn from the standard.
It actually makes the magnitude of the melting point
lower because impurities decreases the quality of a
material. The melting point is not anymore sharp, but a
range of values. The more impurities present, the
greater the range of values.

17. QUESTIONS
3. How can melting point be used in identifying
and/or characterizing unknown compounds?
 Compounds are identified because each
compound have different melting points. The melting
point value can then be matched to a table of
melting points to identify the unknown.

18. APPLICATION
Melting points of organic solids are useful to organic chemists because:
 They (and other physical constants) aid in the recognition of such
compounds. Extensive tables have been compiled, giving the
melting points of different compounds and their derivatives.
 They aid in obtaining information about the purity of an organic
compound. A pure organic compound has a "sharp" melting point.
 They are useful in establishing the identity of a solid compound:
Mixed Melting Point Determination. This technique is based on the
fact, that one substance will lower the melting point of another
substance if mixed with it. A "mixture" of two specimens of the
identical material, by contrast, shows no change in melting point.

19. GENERALIZATION
By performing this experiment, we learned that the more carbon a
chemical or compound have, the higher the melting point.
Salicylic acid got the highest melting point among the three
because electrostatic bonds between the constituents of
molecules of salicylic acid are increasing over time through a series
of additions of heat than those between acetanilide and benzoic
acid. It needs more heat or energy to melt. Melting Point tells us
that it is something about the forces that hold the molecules
together, and the fact that some substances are not molecules at
all, but networks of atoms held in place by either ionic or covalent
bonds. It is the formation of a network of interconnected atoms
that makes for the high melting point, not the type of bonding
between the atoms.

20. GENERALIZATION
It is those compounds which do not form networks that
have lower melting points, because weaker Van der
Waals forces are the only forces keep the molecules
together.