scientific theories for hypothesis :)

Heyy everyone! :)

Well id just like to say that im really glad with the progess im making for my srp, in terms of getting the results all neatly sorted and put together, and all of the backfround research im doing! Currently i have a lot of background research and i am still planning on doing more, so its going to be hard trying to condense it all for the report! :s

Anyway, this was the first initial hypothesis that i stated: That the water in the glass with no cover and no chlorine content will evaporate the fastest, followed by the chlorinated water with no cover, followed by the chlorinated water with the liquid pool cover and finally the chlorinated water with the solid pool cover will evaporate the slowest.

But obviously from my results, this was refuted and incorrect. From the results obtained, it was actually, that the chlorinated, pool water evaporated the fastest, followed by the plain tap water, followed by the chlorinated pool water with solid pool blanket, and finally the chlorinated pool water with liquid pool cover evaporated the slowest.

WELL, i will now just separate the different measuring cups. In terms of the plain, tap water and measuring cup 2 with just the chlorinated pool water, as to which one would evaporate the fastest. There were two scientific theories/ explanations i found. But the problem was there were both conflicting, and the explanations opposed each other. So as a result i had to make an educated guess, but obviously i was wrong. Oh well, this experiment was a good way to test which theory was correct. So anyway, here were the 2 theories:
1. chlorinated water will increase boiling of water and thus less evaporation is expected
http://www.sciencebase.com/science-blog/how-does-salt-affect-the-boiling-point-of-water.html

2. Surface tension - Assuming that a lower surface tension will mean faster evaporation the water with the chlorine content will evaporate faster than the tap water with no chlorine content.
http://www.physicspost.com/physicsforums

well obviously as you can see for my first, initial hypothesis, i went with the first theory which stated that chlorinated, pool water would increase the boiling point of water and therefore less evaporation is expected. But this was incorrect as tested by my experiment. This must mean that the theory about the lower surface tension creating faster evaporation must be true.
Well since i didn’t know much about surface tension i decided to do some research to help understand what it was all about!

What exactly is surface tension?
Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with gas, acts like a thin elastic sheet. This term is typically used only when the liquid surface is in contact with gas (such as the air).

So theory 2 suggested that lower surface tension meant faster evaporation. Well simply put, lower surface tension just means that the molecules are dispersed over a greater surface area, as opposed to high surface tension where the molecules are dispersed over a much smaller surface area.

Examples of surface tension:
Ok, so i found a lot of examples of surface tension. But these were the ones that i thought were the most interesting:
Drops of water. When using a water dropper, the water does not flow in a continuous stream, but rather in a series of drops. The shape of the drops is caused by the surface tension of the water. The only reason the drop of water isn't completely spherical is because of the force of gravity pulling down on it. In the absence of gravity, the drop would minimize the surface area in order to minimize tension, which would result in a perfectly spherical shape.

Insects walking on water. Several insects are able to walk on water, such as the water strider. Their legs are formed to distribute their weight, causing the surface of the liquid to become depressed, minimizing the potential energy to create a balance of forces so that the strider can move across the surface of the water without breaking through the surface. This is similar in concept to wearing snow shoes to walk across deep snowdrifts without your feet sinking.

Needle (or paper clip) floating on water. Even though the density of these objects are greater than water, the surface tension along the depression is enough to counteract the force of gravity pulling down on the metal object.

References:
http://www3.interscience.wiley.com:8100/legacy/college/cutnell/0471713988/ste/ste.pdf
http://hyperphysics.phy-astr.gsu.edu/hbase/surten.html
http://en.wikipedia.org/wiki/Surface_tension

xoxo Mira