Background Information
The physical property that we had to investigate was viscosity. Viscosity is the quantity which describes a liquid’s resistance to flow. “Fluids resist the relative motion of immersed objects through them as well as to the motion of layers with differing velocities within them.” (Elert, 2015)
When the Intermolecular Forces of the substance are strong, the rate of viscosity is larger; and as weak as the IMF’s are, the lower the viscosity of the liquid is. The opposite of viscosity is fluidity, so when the viscosity is low, the liquid is fluid, while if the viscosity is high, the liquid is viscous.
Viscosity is affected by temperature; when we heat the liquid, its viscosity will decrease easily, whereas if we cool it down, its viscosity will increase. This happens because when we increase the temperature, we are giving molecules energy, so the average speed of the molecules increases. This results in the molecules being less time stuck to each other. In conclusion, when we rise temperature, intermolecular forces decrease and molecules interact without being pulled down by each other. On the other hand, when we freeze or cool down the liquid, we are taking away energy from the molecules, so they will move slower and will make contact for longer, increasing the viscosity. (Wen, n.d.)
Acetate
An acetate is an anion (negative ion) which is commonly found in aqueous solutions. It’s chemical formula is: C2H3O2. If the acetate ion is present in solution, then there must also be a cation together forming a soluble salt. A small fraction of the acetate ions will react with water, to make CH3COOH and hydroxide ion.
It is usual to find neutral molecules formed by the combination of an acetate ion and a positive ion (cation), the most common one is hydrogen acetate.
Hypothesis
The stronger the Intermolecular Forces of the chemical are, the more viscosity the liquid will have. This happens because the bonds made between the elements are stronger, so they create a stronger structure, which stops the ball from falling down easily.
Data
Table 1:
Time the ball takes to reach the bottom of the tube (seconds)
| ||||
Propyl Acetate
|
Methyl Acetate
|
Ethyl Acetate
|
Butyl Acetate
| |
TRY 1
|
1,25
|
1,34
|
0,57
|
0,48
|
TRY 2
|
0,79
|
0,84
|
0,57
|
0,38
|
TRY 3
|
0,53
|
0,34
|
0,47
|
0,40
|
TRY 4
|
0, 85
|
0,60
|
0,53
|
0,69
|
TRY 5
|
0,79
|
0,69
|
0,60
|
0,62
|
Average
|
0,79
|
0,69
|
0,57
|
0,48
|
Conclusion
The chemical in which the ball took more time to reach the end of the tube was Propyl Acetate, with an average time of 0,79 seconds, so it looks like it has a stronger intermolecular forces, which is hydrogen bonding.
On the other hand, the chemical in which the ball took less time to reach the end of the tube was Butyl Acetate, with an average time of 0,48 seconds, so it looks like it has a weaker intermolecular forces.
Evaluation
The principal error of this experiment probably has been that the plasticine ball went down through the test tube really fast, so we did not stop the stopwatch in time, which results so instead of using plasticine it could be use a material that took more time to go down through the test tube, use a bigger test tube or even for the timing use a computer program to measure the time electronically. In addition to this we probably didn't drop the ball from the same height all the time, so to solve this we could be conscious about it or establish a certain height (for example 8 cm) to drop the ball every time.
When taking the time was quite imprecise as it took less than a second, so it was very difficult to stop the stopwatch at the exact time it has reached the bottom of the test tube.
As human errors the principal one could be if they are not well labeled to mess up with the acetates and think that one type is another.
Step 5 (return the liquid of the measuring cylinder into its container and retrieve the balls) could be a problem if you didn´t remember in which test tube was each acetate, so probably the best way to solve this could be to do the experiment first with for example propyl acetate, then with methyl, ethyl and butyl .
Bibliography
Elert, G. (2015). Viscosity - The Physics Hypertextbook. Physics.info. Retrieved 21 January 2015, from http://physics.info/viscosity/
Wen, C. Viscosity - Chemwiki. Chemwiki.ucdavis.edu. Retrieved 21 January 2015, from http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Bulk_Properties/Viscosity
Royal Society of Chemistry,. Acetate | C2H3O2 | ChemSpider. Chemspider.com. Retrieved 23 January 2015, from http://www.chemspider.com/Chemical-Structure.170.html
