Preparing a Schlenk tube

We need the following materials for the preparation of a Shlenk tube:

- Schlenk tube
- Stop cock
- Cap of schlent tube
- Some vaseline
- Two elastic bands

The first step is to put some vaseline in the stop cock, so that when we insert it in the schlenk tube it moves easily.
Now, hold the schlenk tube with your left hand and make sure the stop cock is perpendicular to you. With the right hand,  hold the elastic band down the stop cock and pass it straight over the top of it. Next, twist it once, and go back over and twist it again, go back over and finally go the way down; This way, we assure that the stop cock does not come out.

In the last step to prepare the schlenk tube we need to put the cap on its corresponding place. With the second elastic band; we double the elastic band and put it over one metal hook and pass it underneath and then put it over the opposite metal hook.

Now, the schlenk tube is ready to be used.

Lab Session 1 - The Properties of Substances

Objective: To study, evaluate and compare the properties of several substances and relate them to their type of bonding (ionic, covalent or metallic).

Results:

Test tube A.

• The substance is sodium carbonate: white, thin, soft, dust…The sodium carbonate has a high melting point [More than 3 minutes and still didn´t melt].
• Sodium carbonate is soluble in water.
• Not soluble with acetone.
• Sodium carbonate is not a conductor in solid state.

Test tube B.

• The substance is paraffin: little white marbles. The paraffin has a low melting point [Less than a minute].
• Paraffin is not soluble in water.
• Not soluble with acetone.
• Paraffin is not a conductor in solid state.

Test tube C.

• The substance is starch: similar to sodium carbonate, white dust. The substance has a low melting point [Immediately it started melting].
• Starch is soluble in water.
• Not soluble with acetone.
• Starch is not conductor in solid state.

Test tube D.

• The substance is iron: brown, like sand. The substance has a high melting point [More than 3 minutes and still didn´t melt].
• Iron is not soluble in water.
• Not soluble with acetone.
• Iron is not conductor in solid state.

Tables: 

              
Table 1: Shows the results obtained during our performance of the experiment.

SUBSTANCE	MELTING POINT	TYPE OF BOND	SOLUBILITY IN WATER	SOLUBILITY IN ACETONE	CONDUCTOR IN SOLID STATE	CONDUCTOR IN LIQUID STATE
Sodium Carbonate	High	Ionic	Soluble	Insoluble	No	Yes
Paraffin	Low	Covalent	Insoluble	Insoluble	No	No
Starch	Low	Covalent	Soluble	Insoluble	No	No
Iron	High	Metallic	Insoluble	Insoluble	Yes	Yes

Table 2: Shows the expected results of the experiment (results we should obtain).

              

SUBSTANCE	MELTING POINT	TYPE OF BOND	SOLUBILITY IN WATER	SOLUBILITY IN ACETONE	CONDUCTOR IN SOLID STATE	CONDUCTOR IN LIQUID STATE
Sodium Carbonate	High	Ionic	Soluble	Insoluble	No	Yes
Paraffin	Low	Covalent	Insoluble	Soluble	No	No
Starch	Low	Covalent	Soluble	Soluble	No	No
Iron	High	Metallic	Insoluble	Insoluble	Yes	Yes

Conclusion: 

As the method was not 100% precise, we did not expect to do the experiment with 100% of success, however we did the experiment as it was expected. From the results we can observe that these covalent bonds have a low melting point and ionic and metallic bonds have a high melting point. Also none of the substances are soluble in acetone, whereas sodium carbonate and starch are soluble in water. Sodium carbonate is the only substance which has conductivity in liquid but not in solid state. Meanwhile starch and paraffin are not conductors either in solid neither in liquid state, iron is conductor in solid and in liquid state.

As we can see starch can dissolve in water because is a simple covalent molecule meanwhile paraffin cannot dissolve in water because it is a giant covalent structure. Simple covalent structures have low melting point, are not conductors and can dissolve in water as they are not as strong as giant covalent structures and molecules can be broken down. Giant covalent structures have high melting point, variable conductivity and are not soluble in water because are too strong to be broken. Water is a polar molecule and paraffin will not dissolve in it because of its non-polar characteristics. Meanwhile starch will be soluble in water as it is a polar molecule like water.

Evaluation:  

The principal error the method has is probably that it does not specify the quantities necessary for each substance, so we suggest to define the quantities. In case the quantity necessary is not specified, to measure the same amount of each substance we could use a measuring cylinder which measures how much of the substance we are using before we start with the real experiment. Another option is to weigh the amount of the substance we are going to use, and specify an unique quantity for every substance. To weigh we would need a scale.

In addition to this, if time was specified it would be easier to identify its melting point, solubility and conductivity. We could more accurately measure the melting points if like we said before we had a specified amount of time which stays constant for each substance. Another way to measure its melting point would be with a melting point apparatus, which is an instrument which includes a thermometer that measures the temperature at which the substance melts.

Melting Point Apparatus (Wikipedia, n.d.)

References:

Useful informational references:

- Bbc.co.uk,. (2014). BBC - GCSE Bitesize: Ionic formulae. Retrieved 13 October 2014, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/ionicrev3.shtml 

- Hyperphysics.phy-astr.gsu.edu,. (2014). Chemical Bonds. Retrieved 13 October 2014, from http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html

- School-for-champions.com,. (2014). Polar and Non-Polar Molecules by Ron Kurtus - Succeed in Chemistry: School for Champions. Retrieved 12 October 2014, from http://www.school-for-champions.com/chemistry/polar_molecules.htm#.VD4qXfl_vX4

- ScienceDaily,. (2014). Chemical bond. Retrieved 12 October 2014, from http://www.sciencedaily.com/articles/c/chemical_bond.htm

- Sciencesfp.com,. (2014). This area is password protected [401]. Retrieved 13 October 2014, from http://www.sciencesfp.com/lab-sessions-and-blog-tasks.html

References we used:

- Crystal Structure of Sodium Carbonate Monohydrate, Na2CO3. H2O. Zeitschrift Für Kristallographie - Crystalline Materials, 95(1). doi:10.1524/zkri.1936.95.1.266

- Bbc.co.uk,. (2014). BBC - GCSE Bitesize: Ionic formulae. Retrieved 15 October 2014, from http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/periodic_table/ionicrev3.shtml

- Wikipedia,. (2014). Paraffin wax. Retrieved 15 October 2014, from http://en.wikipedia.org/wiki/Paraffin_wax

- Candlescience.com,. (2014). Paraffin Wax for Candles | Candlescience - CandleScience. Retrieved 15 October 2014, from http://www.candlescience.com/wax/paraffin-wax

- Chemistryexplained.com,. (2014). Starch - Chemistry Encyclopedia - structure, reaction, molecule. Retrieved 15 October 2014, from http://www.chemistryexplained.com/St-Te/Starch.html

- Wikipedia,. (2014). Iron. Retrieved 15 October 2014, from http://en.wikipedia.org/wiki/Iron

- Wikipedia,. Melting point apparatus. Retrieved 29 November 2014, from http://en.wikipedia.org/wiki/Melting_point_apparatus