Do all Liquids Evaporate at the Same Rate? Josh Lorschy. Acknowledgements: Michelle Lorschy Financial Support

Transcription

1 1 Do all Liquids Evaporate at the Same Rate? Josh Lorschy Acknowledgements: Michelle Lorschy Financial Support

2 2 Abstract This study was investigating the rate at which different liquids evaporate. Through exploring various pieces of literature, it could be determined that the rate of which a given liquid will evaporate largely depends on the amount of energy it requires. The amount of energy needed for evaporation to occur in separate liquids will vary according to intermolecular forces, density and molar mass. By examining the individual characteristics of a given liquid, the rate at which the several liquids evaporate could be theorised. 250mL of each liquid were poured into separate measuring cups. These were positioned outdoors for 7 days and the remaining liquid was recorded daily. This experiment was repeated 3 times simultaneously. From this experiment, it could be concluded that all liquids evaporate at various rates, according to each liquid's specific properties. Nail polish remover evaporated the fastest, followed by water, salt water, vinegar, orange juice and oil. Following this investigation, it could be researched as to which external factors can alter the rate of evaporation, for example temperature or surface area. Another interesting sector includes how the salinity of water can affect how fast it evaporates. Background Information: Evaporation occurs when a molecule on the surface of a liquid escapes into the air as it changes to a gas. This takes place in vast water sources all over the world. Almost 90% of the humidity in Earth s atmosphere is contributed through evaporation from oceans, lakes and rivers (United States Geological Survey 2014). Evaporation is a useful tool to efficiently separate a solute from a solvent. Table salt, magnesium, potash and bromine can all be effortlessly acquired by evaporating seawater in a controlled environment (United States Geological Survey 2014). For the process of evaporation to occur, the molecules require a definite amount of energy. This is obtained through heat, as an increased temperate will allow the molecules to have higher energy. However, evaporation is all about the energy of each individual molecule. Although a thermometer can measure the temperature of a system, it only calculates the average energy of the molecules in the liquid. Not all molecules have the same energy, which is why evaporation can occur even if the liquid isn t boiling. There would be trillions of molecules moving in random paths, bouncing into each other. An increase in temperature raises the kinetic energy of the molecules (Purdue University 2004). As a molecule bumps into another, it transfers energy; so one molecule ends up with more energy than the other. Single molecules then build up enough strength to become gaseous. The partnership of electron couples between atoms, which make up a molecule, are known as intramolecular forces (Purdue University 2004). These bonds are nearly 25 times more powerful than intermolecular forces. Intermolecular force is the attraction

3 3 between adjacent molecules (Purdue University 2004). To evaporate, the molecules in a liquid need to build up enough energy to overcome the attraction of neighboring molecules (University of Wisconsin- Madison). Molecules in a liquid are always continually moving, so as they are in motion the intermolecular bonds consistently fracture and repair (Dr. Mabel Rodrigues 2012). The build up of energy neutralises the intermolecular forces, as the molecules begin to travel too fast to form the bonds (Purdue University). This allows the molecules to separate, so that individual molecules may vaporize (University of Wisconsin- Madison). As a result, moisture in the atmosphere is made up of molecules, which have used kinetic energy to escape the liquid (Helen Schember, PhD). As explained above, the rate of evaporation is dependent on the amount of energy of individual molecules in the liquid. The volume of power needed to vaporize a liquid comes down to the physical characteristics of the liquid (Dr. Mabel Rodrigues 2012). This is because different molecules require varying quantities of energy to evaporate. Heavier molecules need more energy than lighter molecules, as more mass requires more power. Similarly, the density of a given liquid will affect the rate at which liquids can heat up, and therefore evaporate. Finally, liquids in which the forces between molecules are more powerful will take longer to build up the energy to break free of the liquid. Characteristics of Liquids Liquid Density (g/cm 3 ) Boiling Point ( c) Molar Mass (g/mol) Water Orange Juice n/a Nail Polish Remover (main component is acetone) Vinegar Salt Water n/a Olive Oil

4 4 Aim: To determine if the type of liquid affects the rate at which it evaporates into the atmosphere. Hypothesis: That liquids evaporate at different rates according to their physical characteristics. In this experiment, liquids will evaporate from fastest to slowest in the following order: nail polish remover, water, salt water, vinegar, orange juice and oil. Materials: 18 x 50mL plastic measuring cups with a 10cm diameter - $1 from Hot Dollar 750mL water 750mL salt water (please see appendix) 750mL white vinegar - $3.17 from Coles 750mL nail polish remover - $18.42 from Coles 750mL orange juice - $2.41 from Coles 750mL vegetable oil - $4.21 from Coles Table SAFETY: 1. Liquids may be harmful to ingest they were kept out of reach from small children and animals by being placed on a table 2. Liquids could be damaging to eyes glasses were worn to protect eyes from potentially splashing liquid 3. Spilt liquid could pose a hazard any spilt or excess liquid was wiped up and disposed of in a bin Method: 1. 3 separate measuring cups were filled with 250mL of water each 2. Step 1 was repeated with nail polish remover, vinegar, salt water, orange juice and oil 3. All the measuring cups were positioned on a table, outside but undercover for 7 days 4. The remaining liquid in each measuring cup was noted daily and recorded in a table

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6 6 Results: Remaining Liquid Over 7 Days Remaining Liquid (ml) Days Water Salt Water Vinegar NPR OJ Oil *The above graph is made up of averages from a repeated experiment; to see all the raw data please refer to the appendix *In the above table, NPR stands for Nail Polish Remover *In the above table, OJ stands for Orange Juice

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8 8 Discussion: The hypothesis in this experiment was supported, as the liquids were found to evaporate at different rates. The nail polish remover evaporated at the quickest rate, on average 241mL over the 7 days. The next fastest was water, which evaporated 85mL over the course of the experiment. This was closely followed by salt water at 72mL, vinegar at 63mL and orange juice at 57mL over the week. Finally, the oil didn t vaporize at all over the study of this experiment. These results were obtained because the characteristics of each liquid affects the efficiency of its ability to evaporate. For vaporisation to take place, the molecules in each liquid must build up a certain amount of energy, which is largely dependent on the properties of the liquid (Purdue University). Evaporation is when a molecule escapes from the surface of a liquid as it vaporizes. This occurs when an individual molecule builds up enough energy, so that it moves too fast to form bonds, and therefore becomes gaseous (Dr. Mabel Rodrigues 2012). As a result, the rate at which a liquid evaporates comes down to the weight of each molecule, the forces between each molecule, and the density of the liquid. Nail polish remover is primarily made up of a chemical known as acetone. It has an extremely low density of 0.788g/cm, a low boiling point of 56 c and a molar mass of 58g/mol. This means that the liquid has fewer molecules, with weak intermolecular bonds and molecules that have a low mass (Helen Schember, PhD). These properties were significantly less than the various liquids, which is why compared to the other substances, nail polish remover evaporated at such as fast rate. Water has a lower molar mass at 18g/mol, however has much stronger intermolecular forces, with a boiling point of 98.8 c. Consequently, water requires a considerable amount of energy, significantly larger than for nail polish remover, to evaporate. Salt water has a slightly higher density and boiling point, but not enough to make a difference. Despite this, it still evaporates at a noticeably slower rate, which is due to the impurities in the liquid, bringing the molar mass to 76g/mol. The salt creates inconsistencies in the liquid, which means it takes longer to evaporate as the air pressure is lower. Additionally, only the H2O evaporates and the salt is left behind as residue, which became noticeable by day 3, requiring more energy to evaporate the water molecules (United States Geological Survey 2014). Vinegar has a higher density of 1.05g/cm 3 and a much higher boiling point. The makeup of vinegar is acetic acid diluted in water. This means that the water is vaporized, and left behind tiny crystals, which became visible by day 4. Similarly to the salt water, these impurities cause the evaporation rate to lengthen (Purdue University 2004). Furthermore, the strong intermolecular forces caused the need for more energy for molecules to escape. Similarly, the orange juice, also primarily water, leaves behind pulp when evaporated. It has an extremely higher molar mass of 180g/mol. This means the molecules require a greater amount of energy to vaporize. Finally, the oil didn t evaporate at all. This is largely due to the incredible rise in boiling point of 91 c and molar mass of 346g/mol, both almost double the properties of other liquids. Oil has large molecules and strong intermolecular forces. As a result, the energy

9 9 required for oil to evaporate is too high for the liquid to obtain from the surrounding environment. If the experiment had been over a longer period of time, perhaps a noticeable change may have been identified. This experiment was fairly reliable, however it did have its limitations. Firstly, the measuring cups were located outside, but undercover. Although this was to prevent rain from contaminating the experiment, it meant the liquids didn t have direct access to the sun or sky. The experiment was also subject to other elements of the surrounding environment, including dust and bacteria in the air. The orange juice started to grow a thin layer of mold over parts of the surface of the liquid, which may have affected the results. Likewise, the weather also altered every day and so affected the amount of liquid that vaporized. These sources of error could have been eliminated by placing the test substances in a controlled environment, whereby the temperature is always the same and the air is purified. Secondly, the markings on the measuring cups weren t as detailed as would have been ideal. Although the results would have only been marginally different, they could have been more reliable if the markings were more detailed. For future research, it may be interesting to investigate the affect of the surrounding environment on evaporation. For example, surface area, temperature, weather and the material the liquid is in could be examined. It would also be worthwhile to study how salinity alters the evaporation rate. Conclusion: It was concluded that different liquids do evaporate at different rates, according to the physical properties of the given substance. Nail polish remover vaporized the quickest, followed by water, salt water, vinegar, orange juice and oil.

10 10 Appendix: Salt Water: The salinity of water in the ocean is on average 35%. As a result, 35 grams of sea salt was mixed into 1 liter of water until there were no remaining visible crystals. 250mL was then poured into each of the three cups as described in the Method. Raw Results: Day Remaining Liquid (ml) Cup Water Cup Cup Cup Salt Water Cup Cup Cup Vinegar Cup Cup Cup Nail Polish Remover Cup Cup Cup Orange Juice Cup Cup Cup Oil Cup Cup

11 11 Reference List: Computational Knowledge Engine, 2014 Wolfram Alpha, accessed 4 May 2014, < Evaporation of Liquids, n.d., Chem4Kids, accessed 8 March 2014, < Intermolecular Forces, n.d., Purdue University, accessed 1 March 2014, < Physical Properties of Liquids, 2000, University of Wisconsin- Madison, accessed 26 February 2014, < Rofrigues, M 2012, Evaporation Rate, Newton, accessed 26 February 2014, < Schember, H 2001, Water is not the only Liquid that Evaporates, Cornell Center for Materials Research, accessed 26 February 2014, < The Water Cycle: Evaporation, 2014, U.S. Geological Survey, accessed 26 February 2014, <