Chemistry

1. Kurdistan Regional Government of Iraq
Ministry of Higher Education and Scientific Research
University of Zakho
College of Engineering
Petroleum Engineering Department
Practical Chemistry) LAB)
Name of experiment: Melting Point
Name of Student: Taha Sameer Ali
Sample of experiment (A)
Date of experiment :6-11-2019
Group(B)

2. Introduction:
The melting point (or, rarely, liquefaction point) of a
substance is the temperature at which it changes state
from solid to liquid. At the melting point the solid and
liquid phase exist in equilibrium. The melting point of a
substance depends on pressure and is usually specified
at a standard pressure such as 1 atmosphere or 100 kPa.
It is difficult, though, to find a melting point. Usually,
chemists can only obtain a melting range of a 2 - 3oC
accuracy. This is usually sufficient for most uses of the
melting point.
When considered as the temperature of the reverse
change from liquid to solid, it is referred to as the
freezing point or crystallization point. Because of the
ability of some substances to supercool, the freezing
point is not considered as a characteristic property of a
substance. When the "characteristic freezing point" of a
substance is determined, in fact the actual methodology
is almost always "the principle of observing the
disappearance rather than the formation of ice", that is,
the melting point.
The temperature at which a solid melts is known as the
melting point (MP) of that substance. The melting point is
a physical property of a solid and can be used to help

3. identify a substance. In practice, a solid usually melts
over a range of temperatures rather than at one specific
temperature. For this reason it is more useful to speak of
a melting point range. Although the term "melting point"
is usually used, what is meant is "melting point range". If
the compound melts over a very narrow range, it can
usually be assumed that the compound is relatively pure.
Conversely, compounds that melt over a wide range are
assumed to be relatively impure. Besides melting over a
wide range, impure solids also melt at a temperature
lower than that for the pure compound. For our purposes
a range greater than 2° is considered to be wide. For
example, if an unknown solid melt at 102-106° C, the 4°
range suggests that the sample is impure. If the unknown
is one of four possible compounds which melt at 102, 104,
106, and 108° C, it is most likely that which melts at 108° C.
To summarize, an impure solid melt over a wide range
and at a temperature lower than that of the pure solid. It
should be noted that “insoluble” impurities such as bits of
filter paper or dust have no effect on the MP of a
substance. To affect the MP the impurity must be soluble
in the solid. Several devices are available for measuring
melting points.

4. Tools:
Clamp and Stand Glass Thermometer Beaker and Paraffin
Capillary Tube Burner Rubber wire gauze

5. Procedure:
• Set up a ring stand with a bunsen burner (which should be attached
to a gas valve using rubber tubing), a ring above it, and wire gauze on
the ring.
• Place a beaker of mineral oil on the wire gauze.
• Place a sample of the compound into a capillary tube and use a thin
piece of rubber tubing as a rubber band to attach the capillary tube to
a thermometer
• Insert the thermometer through a hole in a cork, and clamp the cork
to the ring stand as shown.
• Use the bunsen burner to heat the mineral oil slowly.
• Record the temperature at which the solid in the capillary tube melts.

6. Calculation:
We have tested the melting point of sample (A) and the
results was 100 – 102 °C.
Discussion:
The beginning of melting of sample (A) it was at
100°C and when the sample was fully molten the
temperature was 102°C according to references
That means the benzoyl peroxide its melting point is
100 – 102 °C.
Compound Melting point
benzoyl peroxide 100 – 102 °C

7. Answer to Questions:
1.Define the "melting point" of a substance?
Answer/The temperature at which a solid, given sufficient heat,
becomes a liquid.
2.What is the purpose of determining melting points?
Answer/A pure compound will have a definite melting point, therefore,
the identity of a
substance can be determined or the purity of a substance can be
determined.
3.Why could the rate of heating influence the melting point?
Answer/ If the rate of heating was too high, the substance may melt
before the thermometer has a chance to register the actual temperature.
The melting point will appear to be lower than the actual value.
4.Why should samples for melting point determination be finely
powdered?
Answer/ This makes the heat transfer into the sample more efficient and
reproducible, and also enhances the overall reflectivity of the sample for
easier automated detection of the melt.
5. Why is this method not used for finding the melting points of inorganic
compounds?
Answer/Inorganic compounds have extremely high melting points.

8. References:
* Ramsay, J. A. (1949). "A new method of freezing-point
determination for small quantities" (PDF). J. Exp. Biol. 26 (1): 57–
64. PMID 15406812.
*
http://www.fao.org/fileadmin/templates/agns/pdf/jecfa/cta/63/Benzoy
lperoxide.pdf
*http://www.wiredchemist.com/chemistry/instructional/laboratory-
tutorials/determination-of-melting-point
*https://brainly.com › question
*https://www.wilkes.edu › centers-and-institutes › labs-and-equipment › _docs
*https://www.thinksrs.com › pdfs › applicationnotes › MPProcedure
*https://www.quora.com/Why-are-the-melting-points-of-inorganic-compounds-
not-calculated