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Effect of molar mass of alcohol on the rate of alcohol evaporation measured using temperature probe

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Effect of molar mass of alcohol on the rate of alcohol evaporation measured using temperature probe. Please give proper reference to my IB student, Gina if you use this material.

Effect of molar mass of alcohol on the rate of alcohol evaporation measured using temperature probe. Please give proper reference to my IB student, Gina if you use this material.

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  • 1. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067Candidate Name :Yoojin LeeCandidate Number :002213-067Date of Practical :October 17, 2010 Internal Assessment – Rate of EvaporationResearch QuestionHow will changing the molar mass of alcohol affect the rate of evaporation, represented bythe change in temperature over time, measured using a temperature probe?IntroductionAlcohol1 is an organic compound made out of carbon chain and a hydroxyl functional group.Alcohols differ by CH2 groups and the number of CH2 groups determines the size of thealcohol. Alcohols have general formula CnH2n+1OH. In this investigation, five differentalcohols were tested: methanol (CH3OH) ethanol (C2H5OH), propan-2-ol (C3H7OH), butan-1-ol (C4H9OH), and pentan-1-ol (C5H11OH), increasing by CH2. Ethanol is commonly used forfuel resources and alcoholic beverages, while propan-2-ol is used as a cleaning fluid. Lastly,methanol, butan-1-ol, pentan-1-ol are used for manufacturing chemicals in industry.2Evaporation is a change in phase from liquid to gas. The major factor that determines the rateof evaporation is the intermolecular forces of attraction between molecules. For instance,alcohols evaporate faster than water, because water molecules have stronger intermolecularforces of attraction than alcohols; one H2O molecule can form up to four hydrogen bonds,whereas CnH2n+1OH can only form one hydrogen bond, because only one OH group attachedat the end of the carbon chain. Moreover, the intermolecular forces of attraction also increasewhen the relative molecular mass increases. In this experiment, since only alcohols are tested,1 “Alcohol,” Wikipedia, the free encyclopedia, http://en.wikipedia.org/wiki/Alcohol (accessed January 8, 2011).2 “N-butanol,” Wikipedia, http://en.wikipedia.org/wiki/N-Butanol (accessed January 8, 2011). 1
  • 2. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067the number of carbon chain will determine the relative molecular mass as well as theintermolecular forces of attraction. When the carbon chain is long, the molecule will havelarger surface area, resulting in greater Van Der Waals forces between the carbon chains.As the molecules are converted to gas phase, they absorb heat, cooling the surroundingtemperature. Consequently, evaporation reaction is an endothermic process. Thus, inmeasuring the rate of evaporation, temperature probe is used to measure the decrease intemperature. The faster the rate of evaporation is, the faster the temperature will decrease.Hence, by examining the change of temperature overtime, the rate will be calculated andanalyzed. For this investigation, since the evaporation occurs as soon as the alcohol isreleased, only instantaneous rate will be considered. 2
  • 3. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067HypothesisThe rate of evaporation is represented by the change in temperature over time. Amongmethanol, ethanol, propan-2-ol, butan-1-ol, and pentan-1-ol, the rate of methanol evaporationwill be the fastest, because it has the lowest relative molecular mass, and thus theintermolecular forces of attraction are the smallest, meaning that the methanol molecules caneasily evaporate. On the other hand, the rate of pentan-1-ol will be the slowest, because it hasthe highest mass and the greatest intermolecular forces of attraction. The intermolecularforces of attraction is directly proportional to the relative molecular mass when the molecules’properties are the same and the rate of evaporation is inversely proportional to theintermolecular forces. Hence, as the molar mass increases, the rate of evaporation willdecrease. However, longer chains will gradually stabilize and evaporate to a limited extent ornot evaporate at all as the intermolecular forces of attraction gets stronger. ㅣ ㅣ Figure 1 shows the predicted relationship between the rate of evaporation and the molar mass of the alcohol 3
  • 4. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067VariablesVariables Description Method of MeasuringIndependent Molar mass of alcohol Different types of alcohol were chosen: methanol, ethanol, propan-2-ol, butan-1- ol, and pentan-1-ol. Each differs by CH2, and thus increasing the relative molecular mass by approximately 14g. Triplicate trials were performed on each type of alcohol to obtain the mean.Dependent Rate of evaporation Rate of evaporation is represented by the change in temperature over time. Temperature was measured using the ㅣ ㅣ temperature probe on Logger Pro.Controlled Size of the sponge The size has to be identical, because the sponge pieces are directly attached to the probe for absorption of the alcohol sample. The sponge pieces of identical shape and size was prepared using scalpel and ruler. Only well-cut pieces were used for each trial. Type of the sponge For the experiment, a tight sponge was used so that it is easier to cut. Different types of sponge have different absorption rate. Thus, the same type of sponge was used to ensure that the alcohols are absorbed simultaneously. Volume of alcohol For all types of alcohol, 1cm3 of alcohol was released onto the sponge piece. Micropipette was used for accurate measurement and transfer. Temperature In higher temperature, the rate of evaporation will increase. Thus, all trials need to be performed under constant room temperature. Also, the atmosphere has to be windless; otherwise, the rate of evaporation will vary to a great extent. Temperature Probe Since different temperature probes are calibrated slightly differently, in order to prevent random error, the same temperature probe was used throughout the experiment. Alcohol Samples Each alcohol was used from the same bottle to reduce error and each trial was performed immediately to prevent natural evaporation of the liquid. Table 1 shows the independent, dependent, and controlled variables and the methods of measuring 4
  • 5. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067Apparatus Materials  Temperature probe (Logger Pro)  Methanol  Micropipette (± 0.006cm3)  Ethanol  A tight sponge  Propan-2-ol  Styrofoam Box  Butan-1-ol  Scalpel  Pentan-1-ol  Ruler  StaplerProcedure 1. The temperature probe was inserted in a Styrofoam box to prevent change in temperature during experimentation. 2. Identical pieces of sponges were cut using scalpel and ruler and were wrapped around the tip of the temperature probe, fixed with staple at the edge. Figure 2 shows the setup of the experiment 3. Data was collected for a few seconds to ensure that the room temperature was constant. 4. 1cm3 of pentan-1-ol was measured and transferred onto the sponge using a micropipette and the change in temperature was recorded. 5. Steps 2-4 were repeated to obtain the mean for the triplicate trials 6. Steps 2-5 were repeated for remaining butan-1-ol, propan-2-ol, ethanol, and methanol 5
  • 6. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067 Data Collection – Qualitative Data There were no visible changes other than the sponge absorbing the alcohol. During the experiment, the strong smell of alcohol spread as soon as the alcohol was transferred onto the sponge. This shows that the evaporation was surely occurring. All of the alcohol samples emitted strong, pungent smell. Data Collection – Quantitative Data Temperatures of Alcohols with Different Molar Masses (M)/ ℃Time, Methanol Ethanol Propan-2-ol Butan-1-ol Pentan-1-olt/ sec (M=32.0g/mol) (M=46.1g/mol) (M=60.1g/mol) (M=74.1g/mol) (M=88.2g/mol) 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd0.00 16.9 16.5 18.0 25.5 25.0 25.1 25.1 25.7 25.5 25.9 25.5 25.3 18.3 18.0 18.330.0 17.0 16.6 17.9 25.3 24.9 25.0 25.0 25.5 25.3 25.7 25.4 25.2 18.4 18.1 18.360.0 15.4 16.0 16.1 23.9 23.8 23.4 23.9 24.0 24.3 24.9 25.1 25.1 18.0 17.8 17.990.0 12.5 12.4 12.7 22.2 22.0 21.8 22.9 22.8 23.0 25.1 25.2 25.1 17.9 17.8 17.8 120 10.2 9.51 10.2 20.8 20.7 20.5 22.1 22.1 22.1 25.2 25.3 20.8 18.0 17.9 17.8 150 8.52 7.55 8.33 19.7 19.7 19.4 21.5 21.5 21.4 25.3 25.3 25.3 13.1 17.9 17.8 180 7.28 6.21 6.98 18.9 18.8 18.5 21.0 21.1 20.8 25.4 25.3 25.3 18.2 18.0 17.9 210 6.38 5.29 6.00 18.3 18.2 17.8 20.6 20.7 20.3 25.4 25.3 25.3 18.2 18.0 17.9 240 5.76 4.66 5.25 17.8 17.7 17.3 20.2 20.3 19.9 25.4 25.3 25.3 18.2 18.0 18.0 270 5.31 4.24 4.65 17.5 17.3 17.0 19.9 20.1 19.6 25.4 25.2 25.2 18.3 18.1 18.0 Table 2 shows condensed raw data for the experiment extracted from Logger Pro. 6
  • 7. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067Graph 1 shows the raw data for the effect of changing the molar mass of alcohol on the rate of evaporation 7
  • 8. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067Data ProcessingThe absolute value of the gradient of Graph 1 represents the change in temperature over time.Thus, it represents the rate of evaporation. The processed data is shown in Table 3 below. Rate of Evaporation, r/ ℃ s-1 Molar Mass of the Trials Alcohol, M/ g mol-1 Mean(a) Mean ± SD(b) 1 3 3 32.0 0.174 0.129 0.177 0.160 0.027 46.1 0.146 0.119 0.140 0.135 0.014 60.1 0.0669 0.0703 0.0683 0.0685 0.0017 74.1 0.0163 0.0179 0.0182 0.0175 0.0010 88.2 0.0150 0.0134 0.0156 0.0143 0.0017 Table 3 shows the rates of evaporation for different molar masses of the alcohol.(a) Mean: average of triplicate trials for each set.(b) SD: standard deviation for triplicate trials.Sample Calculations ㅣ ㅣ Calculation of the mean rate of 32.0g mol-1 (methanol) from the triplicate trials. Mean ( ) = = 0.160 s-1 Calculation of the standard deviation of 32.0g mol-1 (methanol) from the triplicate trials Standard deviation = = = 0.027 s-1 8
  • 9. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067Data Presentation Effect of Changing the Molar Mass of the Alcohol on the Rate of Evaporation y = -0.0029x + 0.254 R² = 0.94 0.2 (a) 0.16 0.15 0.135 Rate of Evaporation, r/ ℃/s 0.1 0.0685 0.05 0.0175 0.0143 0 0 10 20 30 40 50 60 70 80 90 100 -0.05 Molar Mass, M/ g/mol Graph 2 shows the processed data of average rates of evaporation against the number of the carbon chain. (a) Vertical error bar shows the standard deviation of the triplicate trials for the rate of evaporation. 9
  • 10. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067ConclusionThe data suggests that as the molar mass of the alcohol increases, the rate of evaporationdecreases and that my hypothesis is valid. The linear regression and the R2 value show thatthere is a negative correlation between the rate of evaporation and the molar mass of thealcohol. However, it cannot be proved that the correlation is always true for other types ofalcohol. The rate of evaporation will eventually reach 0 and stop decreasing. When there aremany carbon chains, an addition of another carbon chain will not make any difference,because the intermolecular forces of attraction is already too strong to let the molecules easilyevaporate. At some point, the alcohol is no longer in liquid phase, but in a solid phase due tostrong intermolecular forces of attraction. Thus only for the five sets of alcohol, methanol,ethanol, propan-2-ol, butan-1-ol, and pentan-1-ol, the linear regression is applied. Although,the trend of the results does not portray the overall relationship between the rate ofevaporation and the number of the carbon chain in alcohol, it still supports the fact that therelationship is inversely proportional.EvaluationThe experiment is justifiable because reliable triplicate trials were obtained. Although thestandard deviation of ethanol is relatively wide compared to other types of alcohol, itnevertheless shows a negative correlation, because the standard deviation does not overlapwith other variables. The standard deviations of methanol and ethanol are greater than others,because they evaporated so rapidly but not consistently, since the instantaneous slope of theregression varied a lot. Perhaps, this is due to human error when releasing the alcohol ontothe sponge. Hence, both systematic and random errors were present.Since this experiment dealt with small amount of alcohol to prevent entire soakage of thesponge piece, a constant atmospheric state was vital. For instance, a sudden blow of air could 10
  • 11. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067have increased the rate of evaporation to a great extent.One of the biggest errors came from the temperature when the experiments were performed.Due to the limited types of alcohols provided, ethanol, propan-2-ol, and butan-1-ol weretested during the fall while methanol and pentan-1-ol were tested during the winter. Hence,the room temperature differed by around 7℃, which could have made a huge different in datacollection.Limitations and ImprovementsLimitations ImprovementsWhen cutting the sponge in identical pieces,it inevitably involved human errors.Although it was measured as accurately aspossible with a ruler and cut with a scalpel, In order to improve, more mechanicalthe cross section was not perfectly smooth, methods are needed to produce identicalwhich could have resulted in different pieces of sponges. For example, using athickness. This could have affected the proper paper cutter with a lever and a gridresults to a great extent, because the could produce the pieces more accurately.experiment dealt with a small amount ofalcohol and when the thickness was notleveled well, the probe could not have sensedthe change in temperature properly.The alcohol solutions were released ondifferent parts of the sponge at different pace.Again, this is also an inevitable human error. If the experiment was done in larger scale,Although micropipette was used to adeptly then such minor errors could be negligible.transfer the solution, the results would vary. Using a larger sponge piece with greaterReleasing slowly to make sure the sponge is amount of alcohol solution will yield morewell soaked will produce inaccurate consistent results.instantaneous rate while releasing fast willresult in alcohol solutions dripping from thesponge. Testing a greater variety of alcohols such asOnly a limited number of different alcohols decanol or dodecanol will yield more holisticwas available to be tested, which yielded a results on the relationship between the rate ofresult that could not be applied to a wider evaporation and the molar mass of thevariety of alcohols. alcohol. Table 4 shows the limitations and the improvements 11
  • 12. IB Chemistry HL Name: Yoojin Lee Candidate Number: 002213-067Bibliography1 “Alcohol.” Wikipedia, the free encyclopedia. http://en.wikipedia.org/wiki/Alcohol (accessed January 8, 2011).2 “N-butanol.” Wikipedia. http://en.wikipedia.org/wiki/N-Butanol (accessed January 8, 2011). 12