The document describes a chemistry laboratory experiment to determine the melting point of a solid substance. The purpose is to identify substances and assess purity by measuring the temperature at which the solid transitions to a liquid. The procedure involves filling a capillary tube with the powdered sample, attaching it to a thermometer, and heating the sample while noting the melting range. The student recorded a melting point of 53.5°C for the given substance. Melting points can identify compounds and characterize purity, as impurities lower the melting point range. Well-packing the sample ensures an accurate reading.

1. Technical College Of Engineering
Petroleum and Energy Engineering Department
Chemistry Laboratory
1st
stage
(2016-2017)
Lab # 2(second semester)
(Melting point)
Prepare By:Zanyar nawzad hama ali
Date : 27/5/2017
Group : A

2. The aim of this experiment
The purpose of this experiment is todetermine melting point
temperature of a solidsubstance
Introduction:
A melting point canbe usedto identify asubstance andto get an
indicationof its purity. The melting point of a solidis the temperature
at whichthe solidexists inequilibriumwithits liquidstateunder an
external pressure of one atmosphere. Boththe melting point range
(the interval betweenthe beginning of liquefactionandcomplete
liquefaction) andthe temperature of complete liquefactionare
valuable indicators of the purity of the solidcompound. A pure
crystallineorganic compoundusually possesses asharpmelting point
and it melts completely over anarrow temperature range.
Theory & Backgroundof melting point:
Temperature at which a move happens amongst strong and fluid
stages .
Temperature atwhich harmony exists betweenthe all around
requestedcrystalline state and the more arbitrary fluid state.

3. Equipment:
 Thermometer
 Beaker
 Hot plate
 Capillary tube
 Stand ,clamp, tong
 Watch glass (optional)
 Rubber band
 Spatula

4. Procedure:
1. Powdering the compound and filling of capillary tube:
a) The thinwalledcapillary tube is sealedfromone endby heating it
on a heat source for a few seconds.
b) The givencompound is crushedand it is pushedin the capillary tube
in powderedform. The tube is repeatedly tappedandfilledby the
compound.
2. Fix the tube withthermometer:
a) The capillary is attachedto the thermometer.
b) The whole apparatus is as shownin the Figure.
c) The beaker inwhich the tube has to be placedis filledwithparaffin
or water.
3. Heating the liquidbath:
a) The liquidbath is heatedgently withcontinuous stirring sothat the
constant temperature is maintainedthroughout the liquidusing aglass
loop stirrer moving upand down.
As the temperature reachesnear the melting point of solidthe flame is
reducedand temperature is allowedtorise gradually.
4. Note the melting point:
a) Note the temperature whensubstance starts melting. The
temperature is notedagainwhenthe solidmelts completely.
The average or mean of twovalues gives correct melting point of the
substance.

5. Calculation:
No.
Temperature when
solid starts
melting(t1)
Temperature when
solid completely
melted (t2)
Average =
𝑻𝟏+𝑻𝟐
𝟐
52 55 53.5
T average =
Temperature when solid startsmelting(t1)+Temperature when solidcompletelymelted (t2)
𝟐
T average=
𝟓𝟐+𝟓𝟓
𝟐
=
𝟏𝟎𝟕
𝟐
= 𝟓𝟑. 𝟓 𝒄̊

6. Discussion:
1 -What are the bonding forces that hold togetherthe molecules in a
crystal? Give examples of compounds with such types of bonding
forces.
 Intermolecular forces hold its molecules togethersuch as Van der
Waals forces, Ionic bonding, Covalent bonding, Hydrogen bonding
and Metallic forces.
 Examples:
I2, P8 and solid SO2 =Van der Waals forces. Weaklyheld and easily
broken with low melting points
NaCl, MgO, CaCo= Ionic forces composedofthe electrostatic
attractions of anions and cations. Hard, brittle poor electrical
conductors.
SiO = Covalentbonded crystalforming quartz and diamond
crystals. Hard, poor conductors of heatand electricity and have high
melting points
All of the metallic elements:Ag, Mg, Fe Cu, etc= Metallic bonding
positive ions surrounded by delocalizedvalance electrons. Conduct
heat and electricitywell, have low to high melting points and canbe
soft or hard.
2- What is the effectof 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 lowerbecause impurities
decreases the quality of a material. The melting point is not anymore
sharp, but a range of values. The more impurities present, the
greaterthe range of values.
3- How can melting point be used in identifying and/or
characterizing unknown compounds?
 Compounds are identified because eachcompound have different
melting points. The melting point value can then be matched to a
table of melting points to identify the unknown.

7. 4- Why should you pack the substance well in the melting point
capillary tube?
 If one doesn’t pack the substance wellin the capillary, there will
be air pockets in the capillary. Thus one will obtain a lowermelting
range than the actualrange.
Conclusion :
Melting point of a solid involves the temperature changing from solid
to liquid. Solid and liquid exist in in-equilibrium. The liquid to solid
process is known as freezing or crystallisation. The principle of
observing the disappearance ratherthan the forming of ice is known
as the melting point.