INTERMOLECULAR FORCES

1.    An introduction to the physical property that your group was investigating and how it is related to IMF´s.

My group was investigating the surface tension. We know that surface tension is the energy required to increase the surface area of a liquid due to IMF's. Intermolecular forces can vary depending on the nature or solutes in the liquid. 

So to understand what does Surface tension is we have to know that is measured as the energy required to increase the surface area of a liquid by a unit of area (mm). As stronger IMF, we have a higher surface tension.

To understand better the procedure of the experiment we have to review intermolecular forces and which are the types.

As it names says, intermolecular forces, are the forces in between different molecules.
They control how well molecules stick together and this affects many of the measurable physical properties of substances. The three studied IMF are Van der Vaals force, Dipole - Dipole and Hydrogen Bonding

- Van der Vaals force --> This IMF is founded in all molecules, and is the most weaker type of bonding. The strength of Van der Waals' forces is related to the size of atoms and molecules.The bigger the atom or molecule the bigger the Van der Waals' force.




- Dipole - Dipole --> This IMF are additional electrostatic forces of attraction, only between polar molecules. Dipole - dipole force is stronger than Van der Waals.




- Hydrogen Bonding -->  This IMF are bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar.

Hydrogen bonds are electrostatic forces of attraction between molecules which contain these highly polar bonds. Hydrogen bonding is stronger than van der vaals and Dipole - dipole

2.    A description of the 2 groups of chemicals including; name, structure and types of IMF present.

In group 1 we can find these chemicals: Methyl acetate, Propyl acetate, Vutyl acetate, Ethyl acetate.

All of the chemicals above have Van der Waals force, as I said before, all of the elements have this IMF.

Methyl acetate - Van der Waals and dipole dipole. 



Propyl acetate - Van der Waals and dipole dipole. 




Vutyl acetate - Van der Waals and dipole dipole. 

Ethyl acetate - Van der Waals and dipole dipole.  

I     In group 2 we can find Buthanol, Diethilether reinst, pentane and propionic acid.

Buthanol - All of them. There is a hydrogen molecule bonded to an Oxigen. This makes buthanol have hydrogen bonding appart from the other two 


Diethilethel reinst - Van der Waals and dipole dipole



Pentane - Van der Waals and dipole dipole



Propionic acid - All of them. We can find a hydrogen atom bonded to an oxygen that is why we say it have hydrogen bonding. It also has dipole dipole, apart from Van del Waals.

3.    A prediction (hypothesis) of the results you expect with scientific explanations. 

We expected that as more forces the substance had, surface tension would be higher. More IMF means they are stronger, which should mean there is more surface tension. Following this, Buthanol and Propianic acid should have the highest surface tensions. Particles sticking together creates this tension. We also considered how Molecular Mass affects surface tension and, researching, we founded that as a higher molecular mass, the surface tension should increase. For example, Propyl acetate, and Vutyl acetate, while Pentane, would have a low surface tension.

4.    Suitable tables of results (title, headings, units).

5.    To what extent do your results match what you had expected? 

Internmolecular forces would mean higher surface tension, which matched, they had low  molecular mass, but the IMF compensate and we still got 11mm and 9mm in Buthanol and Propionic acid respectively. 

 We also found, low molecular mass and only 2 IMF, would mean low surface tension, like in Diethilethel reinst (7mm) and Penta (6mm), group 2 went as expected, however, Group 1, even if most of them followed our hypothesis, it was more messy. We got Methyl acetate, that had similar values to Diethilethel reinst, but still got a really high surface tension (11mm, compared to 7mm from Diethilethel reinst), but after that, it went as expected.

Propyl acetate and Ethyl acetate went as expected 102.13g per mol -1 and 8.11g per mol -1 respectively, with only 2 IMF, got us 10mm, which even if the difference in molecular mass was high between them, it makes sense they got the same surface tension, as well as Vutyl acetate, that had higher molecular mass and same IMF, got 11mm instead of 10. 

Our only unexpected result, is Methyl acetate, for the rest, our hypothesis was quite close.


6.    An evaluation explaining areas where error could have occurred and how you would improve these areas in a future investigation.

In general my group worked well allong the whole eperiment and when we were doing it, we didin't notice any possible problems that could had change the expected results or the way of elaborating the experiment. 

Afterwards, when we finished the elaboration of the experiment, we compared the results with other groups of the class which did the same experiment. Some results were different, so our group concluded that there could be some things we should correct, and get preciser results.

Maybe we could make a mistake in the way of measuring the solutions because the way of measuring it using a pipette is not the best way to do it. We can use another way of measuring liquids that can make our results more exact.

Then another point we need to talk about in the evaluation that the way of seeing and measuring how the liquid goes up in the small cristal tube was not also 100% sure. We think this because the small tube was attached with an elastic band to a ruler and the tube was constantly moving upwards and was not in a fixed position. We can solve this problem by maybe sticking with glue the ruler and in that way it would be more fixed and at the time to measure the solution will be better and easier

.

Avoiding this littles things and improving them for the next time, we'll make an experiment more precise. To finish we think we worked well as a group and we didin't had any important problem that might not permit us doing the elaboration of the experiment correctly.

7.    At least 2 references in APA format.

Chemwiki.ucdavis.edu, (2015). Surface Tension - Chemwiki. [online] Available at: http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Bulk_Properties/Cohesive_And_Adhesive_Forces/Surface_Tension [Accessed 25 Jan. 2015].

Bibliografía: Chem.purdue.edu, (2015). Liquids Help Page. [online] Available at: https://www.chem.purdue.edu/gchelp/liquids/tension2.html [Accessed 26 Jan. 2015


Bibliografía: Bbc.co.uk, (2015). BBC - Higher Bitesize Chemistry - Bonding, structures and properties : Revision, Page2. [online] Available at: http://www.bbc.co.uk/bitesize/higher/chemistry/energy/bsp/revision/2/ [Accessed 26 Jan. 2015].

Chemguide.co.uk, (2015). electronegativity. [online] Available at: http://www.chemguide.co.uk/atoms/bonding/electroneg.html [Accessed 26 Jan. 2015].