Research
Ethanol is a compound with the formula, C2H5OH. Ethanol is a clear, colourless liquid, that boils at 78.8° Celsius and freezes at -114.1° Celsius. It is often just called ‘alcohol’. It is also a good solvent – it is able to dissolve many substances that are not soluble in water. It also evaporates quickly, much faster than water. Ethanol is used in wine, aftershave, deodorants and perfumes. Ethanol burns well in air, giving out heat: C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g). There are three types of ethanol (grades): 95% (95.6%) ethanol, Absolute (99-100%) ethanol and Denatured ethanol. 95% (95.6%) ethanol is the highest concentration of ethanol that can be obtained using distillation. Denatured ethanol contains additives such as methanol and isopropanol. Ethanol is a polar molecule. Polarity is ‘the measure of how polar a molecule or bond is. The difference in charge between the positive and negative ends of an electric dipole. The difference in charge between the positive and negative ends of a polar molecule or covalent bond’ . It is polar because it has an OH (hydroxide) component, the high electronegativity of oxygen allows hydrogen bonding to take place with other molecules. Hence, ethanol attracts polar molecules. C2H5 (which is ethyl) in ethanol is non-polar. Non-polar is defined as ‘Bonds or molecules that do not have a permanent dipole. They have an even distribution of charge’ . This also allows ethanol to attract non-polar molecules. This means that ethanol can dissolve both polar and non-polar substances.
Water is a compound of hydrogen and oxygen with the formula H2O. Water can be made in a laboratory. The reaction is: 2H2(g) + O2(g) → 2H2O(g). Pure water is odourless and is nearly colourless. Water is slightly blue and is more visible in larger volumes. Water boils at 100° Celsius and freezes at 0° Celsius. Water has a simple structure, it has two hydrogen atoms and one oxygen atom. Moreover, water is a polar molecule due to its shape which means it is charged both negatively and positively. This type of bond is called covalent bonding because the atoms are sharing electrons and the hydrogen atoms have one electron each. It can be also said that there is an uneven distribution of electrons. Water has a partial negative charge near the oxygen atom due the unshared pairs of electrons, and partial positive charges near the hydrogen atoms.
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When pouring an equal amount (e.g. 50mL of each) of ethanol and water into a measuring cylinder it would be expected that the combined volume would be 100mL. However, the final volume would be around 96mL to 98mL. The reason for this is the size of the ethanol and water molecules. The ethanol molecules are smaller than the water molecule. When the two liquids are mixed to become a solution, the ethanol fills up the gaps left by the water. Both liquids are highly polar and the interaction of the hydrogen bonds from ethanol and water lead to the total volume being less than the combined individual volumes. The size of the volume change varies with the temperature.
Ethanol is soluble in water because ethanol has a -OH group (which is always polar) and a 2-carbon chain (which is always non-polar). As water is polar it attracts the OH group from ethanol. Ethane, which is the carbon chain (only had carbon and hydrogen) does not have a polar group and is not soluble in water. If a hydrogen is bonded to a strong electronegative atom such as oxygen in this case, hydrogen bonds can be formed, since both ethanol and water have an OH (hydroxide) component there can be a hydrogen bond, allowing ethanol and water to be miscible. Miscible means to mix completely to form a homogeneous solution.
Discussion
The results from the experiment indicated some slight fluctuations as the results were not on the trend line but were close for the different volumes of ethanol. As the volume of ethanol was increased, the time had also been increased. With 0mL of ethanol and 75mL of water the average time that it took for the water to reach 50° Celsius from 30° Celsius was 6:34 minutes. With 10mL of ethanol and 75mL of water the average time that it took for the water to reach 50° Celsius from 30° Celsius was 7:25 minutes. In the third trial, 15mL of ethanol and 75mL of water were used, the average time that it took for the water to reach 50° Celsius from 30° Celsius was 8:49 minutes. In the fourth trial, 20mL of ethanol and 75mL of water were used, the average time that it took for the water to reach 50° Celsius from 30° Celsius was 9:08 minutes. And in the last trial, 25mL of ethanol and 75mL of water were used, the average time that it took for the water to reach 50° Celsius from 30° Celsius was 10:21 minutes. The times recorded for all these trials and repeats were consistent but not precise as the times recorded were not exact. The measurements were quite accurate, as using a measuring cylinder rather than a beaker gave more accurate measurements in millilitres. The results were also reliable as the controlled variables were tested. To make this experiment more valid, reliable and accurate additional repeats should have been tested.
The experiment was conducted in a controlled environment. That is, that the amount of distilled water stayed the same. The amount of heat also stayed the same at the maximum setting. The experiment was conducted with a hot plate rather than a Bunsen burner due to the fact that ethanol is flammable. Using a Bunsen burner would have increased the risks of accidents in the experiment. For example, the flame all of sudden could have got out of control, if there was a gush of wind blowing into the laboratory resulting in the ethanol to be on fire and could potentially burn the laboratory. Distilled water specifically was used in this experiment as it is the purest form of water. Moreover, distilled water is water that has been converted into vapor and condensed back into liquid in a separate container. Furthermore, it is known that impurities in the original water that do not boil below or near the boiling point of water remains in the original container. There are three types of ethanol
(grades): 95% (95.6%) ethanol, Absolute (99-100%) ethanol and Denatured ethanol. The ethanol provided for the experiment did not come with any specifications. This means that there could have been two other possible outcomes for this experiment. The results may have varied slightly. While conducting the experiment it was noticed that when pouring 75mL of water into a measuring cylinder and a certain amount of ethanol into another measuring cylinder and then pouring it into another measuring cylinder, the total volume was less than the what the result of the two measurements when added. After researching, it was found that the ethanol molecules are smaller than the water molecules which meant that the volume was going to be less than the result of the two measurements added.
It is unknown why the time taken for the solution to reach 50° Celsius from 30° Celsius increased as the volume of ethanol was increased. As the boiling point of water is 100° Celsius and the boiling point of ethanol is 78° Celsius, it is possible that as these two compounds have a high boiling point it would take longer for the solution to start boiling. Hence, the time increases.
Conclusion
To conclude, the hypothesis was proven to be correct, as the volume of ethanol was increased, the time taken for the solution to reach 50° Celsius from 30° Celsius increased. The results were consistent in the trials hence, making it valid, reliable and accurate.
Bibliography
- Gelling, Cristy. “Which Type of Ethanol Should I Use?” Bitesize Bio, 13 June 2012, bitesizebio.com/13518/which-type-of-ethanol-should-i-use/.
- Helmenstine, Anne Marie. “What Is a Polar Molecule?” ThoughtCo, ThoughtCo, 24 Apr. 2018, www.thoughtco.com/definition-of-polar-molecule-605531.
- Reference . “Why Is Ethanol Soluble in Water?” Reference, IAC Publishing, www.reference.com/science/ethanol-soluble-water-4c7cbb40ace2661d.
- Solubility of things. “Solubility of Alcohols (Eg. Ethanol).” Solubility of Things, www.solubilityofthings.com/water/alcohols.
- The University of Arizona . “The Chemistry of Water.” Chemistry Tutorial, The University of Arizona , 28 Jan. 2003, www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html.
- Triangular Wave Technologies. Water Treatment Home Page, www.triangularwave.com/a1b1.htm.
- Chan, Drew, Richard Hecker, Bob Hogendoorn, Kathryn Hillier, Louise Lennard, Mick Moylan, Pat O'Shea, Maria . Pearson Chemistry 11 New South Wales. Page 178 LF Pearson Australia, 12/2017.
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