Water as Polar Molecule
161: Principles of Living Systems Lab
Water as Polar Molecule
Water is perhaps the most essential molecule for living systems, as it possesses many unique
traits that allow life to flourish. For instance, a low-density solid-state insulates the water beneath,
enabling life to survive during extremely low temperatures (Georgios et al., 2022). Through cohesion
and adhesion, water defies gravity by traveling dozens of feet in the air to nourish plants. Water's
specific heat helps balance environments and regulate climate patterns (Emiliano et al., 2017). These
properties are crucial for supporting life. Water is considered one of the strangest substances ever
studied because its properties are both atypical and essential. In this lab, we will explore the concepts of
polarity, specific heat, and how life has come to depend on water.
Water has a significant impact on the environment around it, which provides us with the
opportunity to form hypotheses by observing its behavior. Assuming that water has a high specific heat
and is polar, we would expect it to heat up at a far lower rate than a substance without hydrogen bonds.
We would also expect water to be influenced by the presence of an electric field due to its polarity. In
contrast, the null hypothesis would state that water does not have a high specific heat or polarity. Thus,
water would heat up at a rate similar to substances without hydrogen bonds and would remain
unaffected by electric fields. This would imply that the life-sustaining properties attributed to hydrogen
bonds and water's polarity would be due to some other mechanism.
Materials and Methods
The laboratory was divided into several stations, each with its own purpose of testing different
characteristics of water. The first station was used to test the specific heat of water as compared to
other substances that lacked hydrogen bonds. The scientific reasoning behind this is that the heat
produced from the hot plate breaks the hydrogen bonds and uses up that energy. This allows water to
absorb a large amount of energy with only a small increase in temperature.
At the first station, we conducted a test to determine the specific heat of water and compared it to
other substances with varying degrees of hydrogen bonding ability. To begin with, we measured 50
milliliters of water, ethanol, and vegetable oil and then poured them into separate Erlenmeyer flasks.
We placed custom rubber stoppers connected to a thermocouple on each flask. Afterward, we placed all
three flasks on the same hot plate and recorded the temperature of each flask every minute for five
minutes.
At the second station, we observed the polarity of water and how an electric field affects it. We filled a
burette with water and placed a basin underneath to catch the water. Next, we rubbed a glass rod with
a rabbit pelt to charge the rod. Once the rod had a charge, we adjusted the stopper to allow a steady
stream of water to flow. We moved the charged glass rod close to the stream of water and performed a
second test with a balloon instead of the glass rod.
We repeated the same test with paraffin oil in the burette. We adjusted the stopper to allow a steady
stream of oil to fall and then brought the charged glass rod near the oil. We also performed a second
test with a balloon instead of the glass rod.
Results
All of our findings can be attributed to the structure of water. The first test that examined
specific heat in comparison to ethanol and vegetable oil illustrated the ability of hydrogen bonds to
absorb energy without rapid changes in temperature. Graph 1 illustrates the resistivity of water to
thermal energy.
Temperature vs. Time
120
Temp (C)
100
80
60
40
20
0
0
1
2
3
4
5
Time (min)
T1: Oil
T2: H2O
T3: ETOH
Graph 1: Temperature vs. Time Graph. Each substance started at relatively similar temperatures. However,
the substances
hydrogen
bonds
increased their
temperature
Eachwithout
substance
increased
its temperature;
however,
waterthe
hadmost.
the least percent change of the
three substances. Oil had a 203% change, ethanol had a 164% change, and water had a 147% change.
The second test observed water polarity and how that is affected in an electric field. Figure 1.
illustrates how water aligns itself in the presence of electric fields.
Figure 1. Caption: The Polarity of Water and Electric Fields. Even in electric fields,
opposites attract. (Granger, 2002)
As the water fell from the burette, it changed its trajectory in accordance with the shape of the
electric field. The electric field did not affect the test with paraffin oil, a substance without hydrogen
bonds. This result was expected and aligns with our current understanding of polarity. Substances that
share electrons equally are considered to be net-neutral molecules. This means that, as a whole, the
charges are balanced and, therefore, unaffected by electric fields.
Discussion
We conducted experiments to analyze water's properties, with a focus on its specific heat capacity and
behavior as a polar molecule. The majority of water's characteristics can be attributed to its polar
nature. For instance, water's ability to resist temperature changes is due to the energy-absorbing
properties of hydrogen bonds (Sokhan et al., 2015). Additionally, the presence of electric fields affects
polar molecules like water, as observed in our second experiment.
Both of our hypotheses were validated, leading to the null hypothesis being rejected. We concluded that
water's polarity is responsible for these phenomena.
While it may seem like these findings have limited significance, they have substantial implications. Many
of water's life-sustaining properties can be traced back to its polarity. These properties, such as
cohesion, adhesion, low-density solid state, and resistance to temperature changes, play crucial roles in
nourishing plant life, stabilizing climates, and creating a habitable environment. Without these
fundamental traits, life as we know it would not be sustainable.
To ensure the accuracy of results and minimize external influences in future repetitions of these
experiments, we recommend several enhancements. For the specific heat experiment, we suggest
providing each flask with its dedicated hot plate, maintaining all substances at a consistent initial
temperature, and ensuring each flask remains at a constant initial temperature throughout the
experiment.
References
Emiliano Brini, Christopher J. Fennell, Marivi Fernandez-Serra, Barbara Hribar-Lee, Miha Lukšič, and Ken
A. Dill Chemical Reviews 2017 117 (19), 12385-12414
DOI: 10.1021/acs.chemrev.7b00259
Georgios M. Kontogeorgis, Andrew Holster, Nomiki Kottaki, Evangelos Tsochantaris, Frederik Topsøe,
Jesper Poulsen, Michael Bache, Xiaodong Liang, Nikolaj Sorgenfrei Blom, Johan Kronholm, Water
structure, properties and some applications – A review, Chemical Thermodynamics and Thermal
Analysis, Volume 6, 2022, 100053, ISSN 2667-3126, https://doi.org/10.1016/j.ctta.2022.100053.
Sokhan, V. P., Jones, A. P., Cipcigan, F. S., Crain, J., & Martyna, G. J. (2015). Signature properties of
water: Their molecular electronic origins. Proceedings of the National Academy of Sciences of
the United States of America, 112(20), 6341–6346. https://doi.org/10.1073/pnas.1418982112
Granger, J. (2002). Water in an Electric Field. The Chemistry of Water, Structure Means
Function. Retrieved 2023, from http://witcombe.sbc.edu/water/chemistrystructure.html.