Question

please show work based on the given data. the problem/question is given under the sub heading CALCULATION

DATA & ANALYSIS YOUR DATA Type of distillation performed: Fractional distel atien. (Attach your GC trace to this write-up sheet) Weights Temperature observed when... distillate_0.30 first distillate collected 66°C residue 0:33 distillation discontinued 80c Sample Composition (from GC results) % n-octane in distillate 23.74 % n-octane in residue 6272% DATA OBTAINED FROM A COLLEAGUE WHO PERFORMED A DIFFERENT TYPE OF DISTILLATIO Data obtained from: Simple distillatwn Weights Temperature observed when .!! distillate first distillate collected 800 residue_103 distillation discontinued 12°2 Sample Composition (from GC results) % n-octane in distillate 37.282 % n-octane in residue 76.95 2 CALCULATIONS Determine the percent completion for both your distillation and your colleague's whose data you obtain other words, what percent (by weight) of the octane/isooctane mixture was collected in the distillate via your calculations on the back. Your distillation: Your colleague's:

this is organic chemistry...

under distillation

Answer 1

Given data:

The following data are given in the question.

Fractional distillation (FD):

Distillate weight = 0.30; n-octane (by GC) = 23.74%

Residue weight = 0.33; n-octane (by GC)= 62.72%

Temperature @ first distillate collected = 66oC

Temperature @ distillation discontinued = 80oC

Simple distillation (SD):

Distillate weight = 1.10; n-octane (by GC)= 37.28%

Residue weight = 1.03; n-octane (by GC)= 76.25%

Temperature @ first distillate collected = 80oC

Temperature @ distillation discontinued = 92oC

Solution:

Key points:

1. Boiling point of n-octane is about 126oC and isooctane is about 98oC.
2. The linear n-octane would have higher volume than the branched isooctane and this is evident from the boiling points of the two compounds.
3. The overriding factor in predicting the retention order in GC is the comparison of the boiling points. Isooctane has lower boiling point and higher vapor pressure than n-octane hence it would elute first in the GC.
4. Base on the key point 3, the GC % are being corrected for calculation. Further, RUN # 146 is considered as the chromatogram for distillate from FD and RUN # 147 is considered as the chromatogram for distillate from SD

Weight % of octane / isooctane in the distillate of FD:

Let us consider, RUN # 146 as the chromatogram for distillate. Based on the key point 3, isooctane eluted first, at RT 0.792 min (62.72%) and n-octane eluted second, at RT 1.281 min (37.29%). Let us consider the weight is in g

Weight of isooctane in distillate = Distillate weight x (% of isooctane / 100) = 0.30g x (62.72 / 100)

= 0.30g x 0.6272 = 0.18816 = 0.19g

Weight of octane in distillate = Distillate weight x (% of octane / 100) = 0.30g x (37.29 / 100) = 0.30g x 0.3729

= 0.11187 = 0.12g

Hence the distillate from fractional distillation contain 0.12g of octane and 0.19g of isooctane.

Weight % of octane / isooctane in the distillate of SD:

Let us consider, RUN # 147 as the chromatogram for distillate. Based on the key point 3, isooctane eluted first, at RT 0.781 min (23.75%) and n-octane eluted second, at RT 1.237 min (76.25%). Let us consider the weight is in g

Weight of isooctane in distillate = Distillate weight x (% of isooctane / 100) = 1.10g x (23.75 / 100)

= 1.10g x 0.2375 = 0.26125 = 0.26g

Weight of octane in distillate = Distillate weight x (% of octane / 100) = 1.10g x (76.25 / 100) = 1.10g x 0.7625

= 0.83875 = 0.84g

Hence the distillate from simple distillation contain 0.84g of octane and 0.26g of isooctane.