The purpose of this lab experiment is to determine whether different ionic compounds containing sodium in ethanol will affect its evaporation rate

         a.  Probe, computer and Vernier’s Logger Pro

5. Computer

1. Vernier’s Logger Pro

6. Weigh boats
7. Balance
8. Ionic compounds in solid state

• NaI
• NaCl
• NaF

9. Spatula (to add ionic compounds onto the weigh boats)

Procedure:

1. Set up the gas pressure sensor close to the station where the measuring will occur so         as not to loose any ethanol if it evaporates

1. Plug it in, attach to the computer
2. Make sure that the probe and the sensor are secure so that no gas leave         through any cracks
3. Open up the computer and start up Vernier’s Logger Pro

2. Weigh the weigh boat on the balance, and press “tare” before adding the ionic substance to the balance
3. Repeat this step four times so one has all of the ionic compound that they need for the first five trials
4. Be careful to set the computer’s mouse to the “collect data” button on Logger Pro
5. Measure 10.0 mL of ethanol in a graduated cylinder

1. At the very end, use a pipette to get a precise measurement and get 10.0 mL

6. Close the ethanol (evaporates quickly)
7. Pour the ethanol from the graduated cylinder into the Erlenmeyer flask
8. Add in the ionic compound
9. Put in the gas pressure probe and secure it tightly before starting to collect data
10. Start collecting data
11. *STEPS 11-14 SHOULD BE DONE QUICKLY AND IN AN ORDERLY FASHION*
12. Collect data for 200 seconds and make a best fit line with the program
13. Save the trial before starting the next one
14. Repeat steps 1-13 for the rest of ionic compounds in the series, and then for the rest         of ionic compounds also

Data Collection:

The Rate of Evaporation of Ethanol (± 0.055kPa/s)* with Different Ionic Compounds

Dissolved in it for 200 Seconds

*Uncertainty calculated collecting data for 200 seconds with the probe in the classroom and then subtracting the range and diving by two:

**Uncertainty calculated by diving the smallest unit (1.0 mL) by two

***Uncertainty calculated by precision of instrument, only measure mass to the tenths        place

Data Analysis and Processing:

Rate of Evaporation (± 0.055 kPa/s) of Different Ethanol Solutions

Average Rate of Evaporation:

• Mean = sum of trials/ # of trials

• Uncertainty= (highest trial – lowest trial) / 2

1. C2H6O: [0.001890 kPa/s +0.001555 kPa/s +(-0.0004033 kPa/s)+(-0.0001292 kPa/s) +        (-0.001599 kPa/s)] / 5=  0.0002627 kPa/s

1. Uncertainty = [0.001890 kPa/s – (-0.0004033 kPa/s)] / 2

         =  0.001147 kPa/s 

2. C2H6O and NaF: (0.005720 kPa/s + 0.003746 kPa/s + 0.002026 kPa/s + 0.005972 kPa/s         + 0.001445 kPa/s) / 5 = 0.003782 kPa/s

1. Uncertainty = (0.005972 kPa/s – 0.001445 kPa/s) / 2

         =  0.002264 kPa/s

3. C2H6O and NaCl: (0.0002420 kPa/s + 0.004792 kPa/s + 0.0009713 kPa/s +                 0.001206 kPa/s + 0.001038 kPa/s) / 5 = 0.001650 kPa/s

1. Uncertainty = (0.004792 kPa/s - 0.0002420 kPa/s) / 2

         =  0.002275 kPa/s

4. C2H6O and NaI: (0.001903 kPa/s + 0.001936 kPa/s + 0.003351 kPa/s + 0.003207 kPa/s + 0.002856 kPa/s) / 5 =  0.002651 kPa/s

1. Uncertainty = (0.003351 kPa/s – 0.001903 kPa/s) / 2

         =  0.0007240 kPa/s

Conclusion:

        In conclusion, the experiment disproved the hypothesis since ethanol with sodium fluoride had the highest rate of evaporation and pure ethanol had the lowest. This can be deduced from the fact that, when averaged out, pure ethanol had an average evaporation rate of 0.0002627 kPa/s while the ethanol-sodium fluoride solution had an average evaporation rate of 0.003782 kPa/s. When looking at the individual trials, there are also some with sodium chloride with a high evaporation point, like trial 2 with a 0.004792 kPa/s rate and also other evaporation points, like 0.001903 kPa/s in the first trial of the solution with sodium iodide. I think that the results came out like this because there must be dispersion forces between the ionic compounds since they’re allowed to move freely. Also, the ethanol also has hydrogen bonds present with its carbons and hydrogens, and that would’ve contributed to it staying in its liquid state for longer. The collected data in the end showed that ethanol solution has the lowest evaporation rate with a 0.0002627 kPa/s average, followed by the ethanol-sodium chloride solution with an average 0.001650 kPa/s rate, then sodium iodide mixed with ethanol with 0.002651 kPa/s average evaporation rate and lastly the sodium fluoride dissolved in ethanol with a 0.003782 kPa/s average rate. Also, the pure ethanol had such different trends and slopes because of the temperature in the room, and it at times it didn’t evaporate.

Evaluation:

This lab experiment was successful at controlling the controlled variables, but the control group had some difficulty because it is nothing similar to the other trials. In the future, something to be improved would to have a more stable room so that the outside pressure isn’t constantly changing and also have the around the same time during the days so that the pressure is more similar. Also, with the help of another person, less time would be lost between pouring the ethanol into the Erlenmeyer flask and getting everything ready before collecting the data, because a couple of seconds passed by before the button was pressed. A good way to control the time so that the trials in each solution were done around approximate times was to have the mass measured out before starting out the experiment so as to be more efficient; another positive thing was that the controlled variables were kept constant throughout the experiment. Something that would help in the future would be to hold more trials, because we can see that with five, proportionately, the difference in some of the trials within each series were very different, and having more reproducible results would give more stable averages. Also, in a more advanced course, creating a vacuum would ensure that there are no other particles in the Erlenmeyer flask besides the ethanol and the solution and also having the same temperature. This is because gases in the air affect the pressure and if they reacted with any of the substances, then it would alter the pressure that the gas pressure sensor collects.