Determination Of Melting Point Science In Motion Clarion

determination of melting point ============================== science in motion clarion university introduction: the melting p

Determination of Melting Point
==============================
Science in Motion
Clarion University
Introduction:
The melting point of a compound is the temperature at which it changes
from a solid to a liquid. This is a physical property often used to
identify compounds or to check the purity of the compound.
It is difficult, though, to find a melting point. Usually, chemist can
only obtain a melting point range of 2 - 3 C accuracy. This is
usually sufficient for most uses of the melting point.
Purpose:
The purpose of this lab is to determine the melting point of various
organic compounds and to use these to identify unknowns.
Equipment and Materials:
Melting Point Apparatus
Glass disks
Digital thermometer that can register temperatures up to 200°C
Spatula per organic compound
Solid Organic Compounds
Metal Forceps
Mortar and Pestle (optional)
Safety:
- Always wear safety goggles in the lab.
- The melting point apparatus gets very hot. Be careful when handling
the equipment.
- Be careful when handling the organic compounds.
Procedure:
1.
Obtain a glass disk and organic compound in the following order:
Phenyl Salicylate
Lauric Acid
Stearic Acid
Vanillin
Benzoin
2.
Using a spatula, place a small amount of the organic compound on
the glass disk and place on the stage area of the melting point
apparatus near the center.
3.
Place the digital thermometer onto the melting point apparatus.
4.
Turn on the melting point apparatus. Adjust the temperature to a
low setting so that it heats up slowly. Continue to slowly
increase the heat if necessary to melt the organic compound.
5.
Observe the organic compound and note the temperature at which the
compound begins to melt. Also observe when the substance has
completely melted.
6.
Record your data in table #1.
7.
Complete procedure 1 – 6, until you have completed all the organic
compounds your instructor has provided.
8.
Obtain unknown samples, and determine its melting point range.
Record your results in data table #2.
9.
Identify the unknown by comparing the melting point range with the
ranges found in data table #1. Record your results in data table
#3.
Data Table #1: Organic Compounds and Melting Point Ranges
---------------------------------------------------------
Organic Compound
Melting Point Range in C
Data Table #2: Unknown Organic Compound and Melting Point Range
---------------------------------------------------------------
Unknown Sample
Melting Point Range in C
Data Table #3: Identification of Unknown Samples
------------------------------------------------
Unknown Sample
Organic Compound
Questions:
1.
Define the “melting point” of a substance.
2.
What is the purpose of determining melting points?
3.
Why is the method not used for finding the melting points of
inorganic compounds?
4.
Why could the rate of heating influence the melting point?
Determination of Melting Point
Teacher’s Notes Continues
Organic Compound
Melting Point Range in C
Phenyl Salicylate
41 - 43
Lauric Acid
44
Stearic Acid
68-69.5
Vanillin
81-85
Benzoin
137
Sodium citrate dyhydrate
150
Unknowns:
1.___________________
2.___________________
3.___________________
4.___________________