SCI 209

3

Seawater Paper

Seawater Paper

The molecular structure of water is what makes it such an unusual molecule. The chemical formula is 2 hydrogen atoms covalently bonded to 1 oxygen atom adjacently. The adjacent bond causes a negative charge to the oxygen atom and a positive charge to the hydrogen atoms. This gives the molecule polarity and it can attract other water molecules and other polar chemicals as well. It works like a bar magnet; the negative side attracts positive ends and vice versa. This also gives water the ability to dissolve materials and contributes to water’s salinity. Salinity is usually 3.5%, however, it changes with depth, temperature, and region. Of the 3.5% of salinity, majority of the chemical elements found are, Chloride (19.2), Sodium (10.6), Sulfate (2.7) Magnesium (1.3) Calcium (.40) and Potassium (.38). That accounts for 34.58% of dissolved materials. A few other materials found in smaller amounts are Carbon Dioxide, Nitrogen, Oxygen, etc., but there are more than 80 elements found in trace amounts in our seawater.

Water’s molecular structure affects it’s physically properties as well as the chemical ones. The melting point for water is 0 degrees C and the boiling point is 100 degrees C, and both are unusually high. Water also stops contracting and rather expands, whereas most other substances don’t increase density in a solid state. Water has a high heat capacity and as Trujillo, A. P., & Thurman, H. V. (2014) explain, “The reason is because it takes more energy to increase the kinetic energy of hydrogen-bonded water molecules than it does for substances in which the dominant intermolecular interaction is the much weaker van der Waals force.” (pg. 134). Because of water’s high latent heat, when water changes state or is heated/cooled, it releases or absorbs high amounts of energy.

Desalination is used to remove dissolved material from water so it is safe for drinking. There are many methods used to do this. With distillation, water is boiled and the vapor is collected and a cooling condenser changes it back into liquid state. This seems like a simple and rewarding process, yet, it takes 540,000 calories for just 1 liter of water, making this method quite pricy. Solar distillation would be the perfect fix, but scientists are having a hard time directing sunlight into a small area to force evaporation and speed up the time it takes. When seawater is frozen, majority of the dissolved materials are excluded leaving behind frozen, fresher water. The ice needs to be frozen and melted multiple times, making it time consuming and using quite a bit of energy. Although, we could melt naturally frozen icebergs which would definitely save time and money.

Countries such as Saudi Arabia get majority (70%) of their fresh water from desalination, so these methods are crucial to certain areas. There are many risks and benefits related to desalination. We could provide water to those in need (1/3 of the population) and in times of need, such as droughts. We also get a lot of our drinking water from aquifers and areas with endangered species. Desalination could give those sources a chance to replenish. Yet, these plants are costly, up to 4 billion dollars in some locations and in order to operate, they need a large amount of energy. It can also have a huge effect on marine life. According to Ackerman, A., (2017), “Disposal of the salt removed from the water is a major issue. This discharge, known as brine, can change the salinity and lower the amount of oxygen in the water at the disposal site, stressing or killing animals not used to the higher levels of salt.” There are many contributing factors with these methods, yet it is very hard to choose between our planet and the well-being of those who reside here.

References

Trujillo, A. P., & Thurman, H. V. (2014) Essentials of oceanography (11th ed.). Boston, MA: Pearson Education

Ackerman, A., (2017) Advantages and disadvantages of desalination plants. Retrieved October 5, 2017 from https://sciencing.com/advantages-disadvantages-desalination-plants-8580206.html