Determination of the Identity of an Unknown Liquid

6 June 2016

The purpose of this experiment is to identify an unknown substance by measuring the density and boiling point. I will be able to conclude which substance is my own from a list of known options stating what its real boiling point and density is.

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My given unknown liquid code is G9R.
This liquid is clear, has a fluid consistency similar to water, and has a strong odour that reminds me of alcohol

When I was reading the Trial 1 temperature on the thermometer I was looking at it from the side, not straight on. When I went to read my next trial I noticed that by viewing it from the front the degrees seemed to actually be a few lower than the optical illusion it gives you from the side. Therefore because my trial 1 is way off from the other two I am not going to count it in my average boiling point calculation.

My procedure was not correct. I did not turn off the gas, and stir gently
while I saw the stream of bubbles coming out of the capillary tube. I left it on until I saw the liquid already being sucked up into it. This may have altered the results of the boiling point to a higher degree than the actual boiling point. Average boiling point = (87.1̊C + 86.6̊C) / 2= 86.9̊C

Average density was the main indicator of my substance I feel because it was the more accurate of the two tests. Boiling point is a lousy indicator because of my incorrect procedure. However that doesn’t make boiling point totally useless.

The only data that was useless was my trial 1 temperature of my boiling point because I was reading the thermometer wrong. 2. The graduated cylinder felt pretty accurate, but I have a steady hand so it may have been easier for me than most others, the literature describes this device as being accurate +/- 0.5 which I got within of very easily.

The volumetric pipette was hard to get the meniscus of the solution exactly right to the 10.00mL line, although the text says it is accurate +/- 0.01, so after a few times of trying to get it as close as possible the solution does end up being very close.

I felt the burette was the most accurate of the three tools because of how slowly the liquid dripped out and how the measurements were already at eye level so gauging the meniscus to the desired amount of solution was very easy. Its accuracy is +/- 0.04 which seems realistic and easy to get within that point.

I would use the burette if I were to repeat this experiment. 3. I felt there were no sources of error in the accuracy of measuring my density. The only experimental error would have been the accuracy of the devices themselves. 4. N

5. I excluded my trial 1 temperature of boiling point for my unknown liquid because I was reading the temperature gauge of the thermometer from the side which I realized was creating an illusion of making the temperature look hotter than it actually revealed from the front of the thermometer.

6. I do not think my boiling point was very accurate because my procedure of the experiment was incorrect. I wrote down the boiling point to be the point when I saw the liquid draining from the test tube, and therefore I thought it must’ve been going into the capillary tube but I couldn’t see because it was clear liquid, going into a clear tube, in clear water and it was hard to differentiate.

7. My boiling point was not as accurate as my density measurements because I was unable to tell the exact boiling point at any given time during my experiment, whereas, I was able to measure the density, +/- the uncertainty in my measuring devices, perfectly. 8. In order confidently determine what substance my “G9R” was I would have to do over the boiling point experiment a couple of more times.

I would turn the gas off and take the Bunsen burner away from the apparatus when the stream of bubbles started coming out from the mouth of the capillary tube. This would allow me to correctly determine when the atmospheric pressure was equal to the vapour pressure.

I can narrow down my unknown substance to either Ethanol or 2-proponal. Ethanol’s density is only 0.001g/mL higher than my own measurements, but its boiling point is 8.4̊C lower than GNR’s.

Whereas 2-proponal’s density is off by 0.003g/mL and its boiling point is only off by 4.5̊C. If I were to make an educated guess I would lean more towards Ethanol. Both the precision and accuracy of my data was far greater in density than in boiling point and Ethanol’s density is closer to GNR’s than any other substance.

Works Cited
Olmsted, John III; Williams, Greg; Burk, Robert C. Chemistry, 1st Canadian ed.; John Wiley and Sons Ltd: Mississauga, Canada, 2010, pp 399 – 406 Koczanski, Krystyna; Xidos, James D. CHEM 1300 Laboratory Manual; UMSU Copy Centre: Winnipeg, MB, Canada, 2013, pp 16

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