Objective
To study, evaluate and compare the
properties of several substances and relate them to their type of bonding
(ionic, covalent or metallic).
Theoretical background
The properties of substances are
related to the kind of bonding present in those substances. The type of bonding
depends on the atoms present and is related to their position in the periodic
table.
Materials
Substances A to D Conductivity meter
Test tubes Distilled water
Spatula Acetone
Bunsen burner
Method
Repeat the procedure for each of the substances
provided:
1. Take ½ a spatula of the substance in
a test tube. Describe the appearance of the substance.
2. Gently heat it in the flame of the
Bunsen burner and state if the approximate melting point. (Low, intermediate or
high).
3. Take ½ a spatula of the substance in
another test tube.
4. Add 10 mL water, stir it and state
whether the substance is soluble in water or not.
5. Repeat the steps 4 and 5 using
acetone instead of water.
6. Using the conductivity meter, state
if the substance is a conductor in solid state.
7. If it the substance is soluble in
water, test whether the solution is a conductor or not.
Table 1: Results taken in class about the properties of the following substances.
Table 1: Results taken in class about the properties of the following substances.
Melting Point
|
Solubility in H2O
|
Solubility in Acetone
|
Conductivity in solid
|
Conductivity in H2O
|
|
Sodium Carbonate anhydrous
|
High
|
Yes
|
No
|
No
|
Yes
|
Paraffin
|
Low
|
No
|
Yes
|
No
|
No
|
Starch
|
High
|
Yes
|
Yes
|
No
|
No
|
Iron Powder
|
High
|
No
|
No
|
No
|
No
|
Table 2: Results that were expected about the properties of the following substances.
Melting Point
|
Solubility in H2O
|
Solubility in Acetone
|
Conductivity in solid
|
Conductivity in H2O
|
|
Ionic bond
|
High
|
Yes
|
No
|
No
|
Yes
|
covalent bond
|
Low
|
No
|
Yes
|
No
|
No
|
covalent bond
|
Low
|
No
|
Yes
|
No
|
No
|
metallic bond
|
High
|
No
|
No
|
Yes
|
Yes
|
Conclusion:
As we can
see in these two tables (mainly the second one), the main characteristics of
ionic compounds are that they have a high melting point; they are soluble in
water, but not in acetone; they don’t conduct electricity in solid state,
however, they do conduct electricity when dissolved in water. All these have to
do with the arrangement and the force experienced within the molecule. As it
has a high melting point, it suggests that it has a quite strong bond and
arrangement (strong electrostatic attractions). As it is soluble in water, but
not in acetone, it demonstrates that it must be polar (water is polar) and as
it is polar, it doesn’t dissolve in non-polar substances, such as acetone. They
don’t conduct electricity in the solid state because in solid state, the strong intermolecular and electrostatic forces keep the particles in a fixed position and hold them tightly together and as there is no flow of particles or electrons, there is no possibility of the electricity to flow. In liquid state, enough energy is given to the substance so particles are able to overcome the intermolecular forces. For this reason, particles start to move around more freely and this way, the flow of charged particles that create the current of electricity is possible. This reasoning for the properties of the substance can be also used in the following compounds.
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In covalent molecules, the melting point is quite low, which suggests that little amount of energy is needed to separate the atoms (weak intermolecular forces). They aren’t soluble in water, but they are in acetone. This demonstrates that covalent bonds are non-polar. They don’t conduct electricity in solid state nor dissolved in H2O. This is because the arrangement doesn’t let the charged particles flow around freely. These properties demonstrate that the substance that we worked in the lab with was a simple molecular covalent compound because giant covalent structures (lattices) have a really high melting point and don't dissolve in water or in an organic solvent.
In covalent molecules, the melting point is quite low, which suggests that little amount of energy is needed to separate the atoms (weak intermolecular forces). They aren’t soluble in water, but they are in acetone. This demonstrates that covalent bonds are non-polar. They don’t conduct electricity in solid state nor dissolved in H2O. This is because the arrangement doesn’t let the charged particles flow around freely. These properties demonstrate that the substance that we worked in the lab with was a simple molecular covalent compound because giant covalent structures (lattices) have a really high melting point and don't dissolve in water or in an organic solvent.
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In metallic bonds, the melting point is high, there are strong intermolecular forces. They aren’t soluble in water or acetone due to their so strong attraction. They conduct electricity either dissolved in water or in solid state because of the continuous flow of electrons.
In metallic bonds, the melting point is high, there are strong intermolecular forces. They aren’t soluble in water or acetone due to their so strong attraction. They conduct electricity either dissolved in water or in solid state because of the continuous flow of electrons.
As we can see reflected in both tables, the experiment went on quite well as the results obtained were really similar to the expected ones, we can just stand out 3 main errors: the melting point in starch; the solubility in water of starch and conductivity in solid of Iron Powder. I will explain why these variations in the results might have taken place in the evaluation.
Evaluation:
Evaluation:
Errors
could have occurred for different reasons:
-The
conductivity of Iron Powder as a solid could have occurred because as the solid
was in really small portions, the space between each portion could have broken
up the flow of electrons. This could be solved getting a big block of this
substance so that there’s no space between each portion.
-When
dissolving the substances, we could have not shaken the test tube enough for
the substance to dissolve and the concepts “high” and “low” are quite subjective.
We could determine a time which serves as a barrier to separate “high” from “low”.
-When
heating up the substance for melting point, the angle in which the test tube is
put may vary how much the temperature rises, if you put it vertically, diagonally
or horizontally, the results change.
-It is almost impossible to take the amount of each substance that we work with but in order to make an aproximation to it, we can weight it each time we get some.
-For the accuracy of the melting points, we could put a thermometer inside the test tube and record the experiment, then slow it down so we can see the temperature more precisely
-It is almost impossible to take the amount of each substance that we work with but in order to make an aproximation to it, we can weight it each time we get some.
-For the accuracy of the melting points, we could put a thermometer inside the test tube and record the experiment, then slow it down so we can see the temperature more precisely
References:
Hyperphysics.phy-astr.gsu.edu,. (2014). Chemical
Bonds. Retrieved 10 October 2014, from http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond2.html
(2014). Retrieved 7 October 2014, from http://www.sciencesfp.com/uploads/2/1/5/9/21597828/1.3_types_of_bonding.pdf
