Mixed Melting Point

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: Mixed Melting Point

Name of Student: Taha Sameer Ali

Sample of experiment (Cinnamic acid B)

Date of experiment :13-11-2019

Group(B)

2. Introduction:

A pure organic compound usually melts over a range of two degrees or less, If
the melting point of a pure compound is within a degree of the value found a
lab handbook it is presumed to be pure, A sample is impure if it has a melting
point range that is lower and/or wider than that the literature value. More
impurities increase this effect. In the organic lab, unless something is wrong
with the procedure or the equipment, a substance generally cannot be
observed to melt at a higher temperature than its melting point! Experimental
melting points should be always reported as a range, for example, 42-44°.A
given sample is only used once for MP determination, always use fresh
samples for additional trials. Dispose of used capillary tubes in the proper
receptacle, not in the wastebasket, for a Pure compound usually melt over a
narrow temperature range, often 1° or less, but for an Impure compound melt
lower than pure compounds and over a wider temperature range. A pure
substance melts at a precisely defined temperature, characteristic of every
crystalline substance and dependent only on pressure (though the pressure
dependency is generally considered insignificant). Determining the MP is a
simple and fast method used in many diverse areas of chemistry to obtain a
first impression of the purity of a substance, identify a substance. In practice,
a solid usually melts over a range of temperatures rather than at one specific

3. 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


Tools:




Clamp and Stand Glass Thermometer Beaker and Paraffin

4. Capillary Tube Burner Rubber wire gauze


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.

5. Calculation:

We have tested the mixed melting point of sample (cinnamic acid B ) and
the results were 97-105 °C.




Discussion:

The beginning of melting of sample (cinnamic Acid B) it was at 97 °C and
when the sample was fully molten the temperature was 105 °C so there
are impurities but with very small amount of it. perhaps there is an issue
with the results here is some difficulties they didn’t use fresh sample or
maybe the sample Deposit into capillary tubes or they didn’t close the
capillary tube well then, we couldn’t have the accurate results or someone
have mistaken with reading the thermometer which occur this problem or
someone has problems with vision that he couldn’t see at which
temperature the sample being melt or fully molten.

6. References:


1) https://quondam.csi.edu/ip/physci/faculty/rex/MPTips.htm



2)http://www.chem.uiuc.edu/weborganic/orglab/mixmp/mixmp.htm



3)https://www.thinksrs.com/downloads/pdfs/applicationnotes/MPProcedure.
pdf


4)https://www.wilkes.edu › centers-and-institutes › labs-and-equipment › _docs