SPARTA HIGH SCHOOL
NONPOLAR, POLAR, IONIC
AND COVALENT
COMPOUND STRUCTURE
AND PROPERTY
LAB NUMBER 1
RACHEL THIES
9/2/2015
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INTRODUCTION
There are two major types of compounds found on Earth. These compounds are ionic and covalent.
They differ in the way that they are bonded. Bonding happens when an atom needs to gain, lose or
share electrons to be stable. All atoms must have a full outer shell of electrons to be stable. Ionic
compounds transfer electrons from the outermost electron orbital from one atom to another.
Generally, they consist of a positively charged metal and a negatively charged nonmetal. These opposite
charges hold the two atoms together. Covalent compounds share electrons rather than transferring
them from orbital to orbital. There is not a positively or negatively charged atom involved in a covalent
compound. Typically, the atoms involved in a covalent compound are both nonmetals. Covalent
compounds may be much bigger than an ionic compound because they can be made up of two to
thousands of atoms at a time. Ionic compounds are known to have much stronger bonds than those that
are covalently bonded. Within these two types of compounds, there is one more characteristic that they
can be classified into: polarity. A polar substance is one that shares electrons unequally and has a partial
positive and a partial negative end. A nonpolar substance shares equally throughout the structure and
will have no charges. Polar substances generally can be dissolved in other polar substances, and
nonpolar substances can be dissolved in other nonpolar substances. This pattern follows the phrase,
“like dissolves like”. Certain polar substances like water can also exhibit a phenomenon called Hydrogen
bonding, which occurs when the partially charged ends of a compound weakly attract nearby
compounds of the same structure.
The purpose of this lab is to investigate the properties of polar, nonpolar, ionic and covalent substances
due to their chemical structure. Examinations were done with each applicable compound such as crystal
structure, hardness, solubility, melting point, and surface tension. Prior to entering lab, predictions were
made. If crystal structures were observed under a microscope, then ionic substances would show
irregularly patterned crystals and covalent substances would show regularly patterned crystals. If
hardness was observed, then ionic substances would show a much higher level of hardness than a
covalent substance because of relative bond strengths. If melting point was observed, then ionic
substances would take a much longer time and higher temperature to melt than a covalent substance
because of relative bond strengths. If surface tension was observed, than the polar substance would
exhibit a force that would allow a small object to float and a nonpolar substance would not allow this
phenomena. If solubility was observed, then a polar substance like salt and sugar would dissolve in a
polar substance like water and a nonpolar substance would dissolve in a nonpolar substance. Unlike
substances, like oil and water; oil and sugar; and oil and salt would not dissolve one another.
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MATERIALS AND METHODS
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Polar ionic substance (salt)
Polar covalent substance (sugar)
Nonpolar substance (vegetable oil)
Polar substance (water)
Two 250 mL beakers
Hot plate
Stirring rods
Compound light microscope
Glass slides
Petri dish
2 paper clips
First the crystal structure was observed under a microscope. To do this, small crystals of each of the
solids, salt and sugar were placed on separate glass slides and placed on the stage to be observed one at
a time. Next, the solid substances were tested for hardness. For this test, a fingernail was used to
scratch and break the solid. An actual numeric value was not recorded, but rather a relative comparison
of each of the solids. Next, each solid substance was measured for melting point. 1 gram each of salt and
sugar were placed in a beaker and placed in the center of a hot plate. A temperature value was not
collected, rather a time value that it took one to melt in relation to the other. Next, surface tension was
examined. To do this, equal amounts (5 mL each) of vegetable oil and water were placed in a petri dish.
A paper clip was placed on the very outer surface of the liquid line in an attempt to have it float. Next,
solubility was tested. To do this, 1 gram of each solid was dissolved in each liquid. Equal amounts (5 mL)
of each liquid were mixed as well. This gave the following potential solubility combinations: salt and
water, sugar and water, oil and water, sugar and oil, salt and oil. Observations were recorded.
RESULTS
In the first test, sugar was arranged into perfect cubes and salt appeared irregularly shaped under the
microscope. In the hardness test, it was found that sugar crystals were much easier to chip with a
fingernail than salt crystals. In the melting point test, the sugar melted in 3 minutes, whereas salt never
changed in state or color. In the surface tension test, the petri dish containing the water was able to
hold a paper clip, whereas the petri dish with the oil alone, the paper clip sunk to the bottom. In the
solubility test, oil and water, oil and sugar, and oil and salt all did not dissolve. The only dissolved
combinations were sugar and water, and salt and water. See Table 1 below for an organized
representation of this data.
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Table 1- Results From Tests 1-4
Test
1
2
Test
Description
Crystal
structure
Hardness
Substance
Result
Salt
Sugar
Salt
Cube
Hexagon
Very difficult
to chip with
fingernail
Very easy to
chip with
fingernail
Neither
melted nor
changed color
Completely
melted and
changed color
within 3
minutes
Paper clip did
not float
Paper clip did
float
Dissolved
Sugar
3
Melting point
Salt
Sugar
4
Surface
tension
Oil
Water
5
Solubility
Salt and
water
Sugar and
water
Oil and water
Salt and oil
Sugar and oil
Dissolved
Did not
dissolve
Did not
dissolve
Did not
dissolve
CONCLUSIONS
In this lab, the purpose was to investigate the properties of the compounds oil, water, sugar and salt and
draw conclusions that relate the structure of that compound to its properties. Looking at the crystals
under the microscope became difficult because of the quality of the microscopes given. However, there
were regularities seen on both crystals. Sugar exhibited hexagonal crystallization, whereas salt crystals
showed perfect cubes when subjected to light. This was different than was predicted. The hardness and
melting points of sugar and salt relate to the bond strengths of those compounds. Because the bond
strength of an ionic compound is generally stronger than one with covalent bonding, then the hardness
and melting point of salt was also greater than sugar, which is just as was predicted. Just as predicted,
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surface tension action was only present in the petri dish, as this is the only compound in the test that
was expected to exhibit hydrogen bonding. The weak attractions between the water molecules held the
paper clip in suspension in the water dish, whereas there were no attractions in the dish with the oil. As
stated in the introduction, salt and sugar are both polar molecules. Because sugar and salt were both
observed to dissolve in water, which is also polar, but not oil, which is polar, the original prediction that
“like would dissolve like” can be supported. All of the original predictions were supported with the
exception of the crystalline structure.
DISCUSSION
Some sources of error in this lab led to the rejection of one of the original predictions. One issue was the
inconsistency of the crystal sizes of the salt. This made viewing the crystal much more difficult. In the
future, a mortar and pestle will be used to combat this issue. Another issue with the crystal structure
examination was the resolve power of a few of the microscopes. The objective seems to show very little
clarity, which made it difficult to conclude at the close of the lab.
It is important to consider the implications that this lab has on real life. Ionically bonded compounds will
generally have a much higher boiling and melting point than covalent compounds because of their
strong bonds. They will tend to be much harder as well. This makes them better at withstanding high
heat than a covalent compound, which can have many industrial benefits. Surface tension is not the only
phenomena that hydrogen bonding is responsible for. Hydrogen bonding will also allow for water to
stick to itself in droplets (cohesion), for water to stick to other materials (adhesion) and for water to rise
up a tube (capillary action). It also makes water stay liquid at a much higher temperature than most
compounds and it also allows it to resist a temperature change (which means that it is slow to heat and
slow to cool) that would cause them to evaporate or freeze. This contributes to the major amount of
liquid water in the world. Water rises up tubes in plants to travel to leaves. With respect to the idea that
“like dissolves like”, this idea that polar substances can only dissolve polar substances and nonpolar
substances can only dissolve polar substances, there is great significance as well. Nonpolar vitamins in
the human body need nonpolar fat or oil to dissolve and be used. Any polar substance can be well
dissolved in water, making it the universal solvent. Oil and water were found to not mix well, which
gives an explanation to why having a nonpolar component to the cell membrane would help it maintain
itsmoisture level.
LITERATURE CITED
None.