Lab Report 1: "The properties of substances and their bonding"

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.

	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. 
                                        

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.

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:

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

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