Table of Contents

Back to list of projects | Introduction | Method | Results | Conclusion | Bibliography |

Introduction


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At the core of our question, we can see that water evaporates faster with increased temperature (steam rising off the ground after rainfall when the sun comes out)[1], and this makes sense, because more excited molecules are more likely to escape their liquid state. Also, surface area increases the rate[2], because there is probably a very small depth at which the molecules can escape. This shallow volume (surface area * depth molecules can escape at) would be increased by higher surface area. Also, wind could affect the humidity (higher humidity saturates the air and slows the rate at which water can enter), and pressure may be a factor as well[3].

Our goal was to find a rate of evpoaration based on temperature, so in the experiment, wind, surface area, and humidity will be controlled, temperature would be independent, and percent of volume lost per minute was the dependent.

Our hypothesis was that the rate of evporation will follow an exponential growth function, where 100% is (almost) instantly vaporized at 100C and the rate of evaporation is 0 at 0 C.

Method


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For our setup, we first filled up a 250ml beaker with water, set the hotplate to a ceratin power level, and then placed the beaker on it. We left the termometer in, so we could observe when the temperature stablilized. Then, I poured out enough water so that only 200ml was left, and took the mass. We then put it back on the hotplate, and took its mass every 5 minutes for 30 minutes total. We recorded these values and repeated our process until we had 5 different temperatures.

The materials were: 250ml beaker, water, hotplate, thermometer, timer, tongs and mass scale.
The annoying thing with the hotplate is that there were no temperature indicators on the adjustment wheel thing, which compelled me to make this picture...


Results


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For our data table, we took the mass and subtracted the mass of the beaker to find the remaining mass of water. After, we converted the remaining mass to a % of the original. After this, we found a trend line for each of the tmperatures, and then placed the slopes of them into another data table. This way, our final trend line equation gives us a way to determine mass lost per mintue based on temperature.
Here is the massive data table...


And after this, we graphed the data, and got graphs similar to the following:


Here is a file containing all the graphs: Graphs
And here is the file containing our data spreaddsheet: Data

Conclusion


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After analyzing our graphs and data, we found exactly what we were looking for. The trend line definitely follows a pwoer function, and this can be seen by an inflection point at approximately 84 C. For this reason, our hypothesis was correct. While the formula for finding the % lost at a given temperature is hardly elegant, we were still both pleased that our data agreed with the hypothesis and made sense. The reason why evaporation occurs faster at higher temperatures is obvious, but whyit si a power function and not linear could be because the distance below the surface that the molecules could escape from could be deeper, and therefore may escape quicker (and on the very surface, molecules are already escaping faster).


Here's the synthesis of all our graphs, we put the slopes of different temperatures onto one final graph.

Our main sources of errow were probably outside disturbances, because we did this on different days, and also the hotplate wasn't very accurate due to its power levels. Lastly, there was some variance in how often we took temperatures, because sometimes taking the mass took longer than other times, so it wasn't exposed to heat for this brief period. Lastly, we think we used the same beaker, but it could have been replaced, or things could have contaminated it. I think doing more trials would give a much more accurate equation for rate of evaporation, but the sheer amount of time each trial took (at least an hour each) would make this a very tedious process.

Related Sites


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[1] http://www.vtaide.com/png/evaporation.htm - More geared for kids, but it is an interactive site for learning about factors that affect evaporation.
[2] http://www.newton.dep.anl.gov/askasci/chem00/chem00964.htm - Someone asks a scientist what factors affect evaporation.
[3] http://www.blurit.com/q316525 - Similar to yahoo answers or wikianswers. Someone asks about what factors affect evaporation.
[4] http://en.wikipedia.org/wiki/Evaporation - You have to reference wikipedia. If you didn't use it you'd be lying.
[5] http://techalive.mtu.edu/meec/module01/EvaporationandTranspiration.htm - Little kid site about evaporation again.
Made by Kevin Stephenson (2010)