I had to do a fractional distillation while my lab partner did a simple distillation. I had 2 unknown compounds which could have been any of the following:
heptane, cyclohexane, toulene, octane,
Well I think I went and boiled the solution a little too quick b/c the liquid which was supposed to be condensing out went and started to come out of the neck of the hickman head...I went and pippeted off 3 ml total of that liquid. Unfortunately I went and pipetted of the forerun as well in the liquid which was mixed together. Out of the original 7ml only 4ml was left and then there was even less from what I could see since the liquid mix must have evaporated alot.
In the end the compound finally leveled off at 110 degrees celcius.
That meant of course that it had Toulene in it but as for the other compound I wasn't certain to the identity. I had observed that the thermometer had leveled off at 90 degrees celcius for awhile though but in my panic I went and pipetted that off as well and got that mixed into the forerun. All I got was 0.5 ml of distillate that I was sure was a certain compound since the temp had leveled off at 110o
The refractive index for the simple distillation for 2 samples, 1 taken at 1ml and 1 taken at 3.5ml was 1.415(1ml sample at 26o) and 1.4724(3.5ml sample at 26o)
For the fractional that I did I never got 1ml of distillate for what I started to keep track of so I just used a sample from my 0.5ml that I had.
I got 1.4804(26o)
I narrowed the compounds based on the refractive index to toulene & cyclohexane
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The thing is that we were told to find out how much of each compound was in each sample unknown. They told us that they had added Decane to each sample.
I don't know how to calculate the percentage of each.
I was told that the impurity of the sample would lower the refractive index that we got for the sample.
an example of the board said this:
Toulene (60%) + ethylbenzene (30%) + Decane (10%)
RI= 1.4967 1.4932 1.4119
RI mix= 1.4967(0.60) + 1.4932(0.30) + 1.4119(0.10)
It isn't explained in my book how to calculate the percentage of each.
Help Please =)
To calculate the percentage of each compound in your unknown samples, you need to use the refractive index values and a mathematical calculation called the refractive index mixture formula. Here's how you can do it step by step:
1. Recall that you have two compounds in your samples: toluene (T) and cyclohexane (C), with an added impurity of decane (D).
2. Determine the refractive index (RI) of each individual compound in pure form. From your information, you have the RI values for toluene (T) and cyclohexane (C), but not for the impurity decane (D). If you have the RI value for decane, you can include it in the calculations.
3. Calculate the refractive index of the mixture (RI mix) using the refractive index mixture formula:
RI mix = RI(T) x %T + RI(C) x %C + RI(D) x %D
In this formula, %T, %C, and %D are the percentages of toluene, cyclohexane, and decane in the mixture, respectively. RI(T) is the refractive index of toluene, RI(C) is the refractive index of cyclohexane, and RI(D) is the refractive index of decane.
4. Now, you have the RI mix value from the refractive index measurements of your samples.
5. Set up two equations using the RI mix value and the refractive index values of toluene and cyclohexane. Since you have two unknowns (the percentages of T and C), you need two equations to solve for them.
Equations:
RI mix = RI(T) x %T + RI(C) x %C
%T + %C = 100 (since the percentages add up to 100%)
6. Solve the equations simultaneously to find the values of %T and %C. You can use substitution or elimination methods to solve these equations.
7. After solving the equations, you will have the percentages of toluene (%T) and cyclohexane (%C) in your samples.
It is important to note that this method assumes ideal behavior of the compounds and may not be entirely accurate due to impurities or other factors. Additionally, the refractive index mixture formula might not be applicable when there are more than two compounds in the mixture.
Hope this helps! Let me know if you have any further questions.