CHEM 2204 Formal Lab Identifying Unknow Essay

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CHEM 2204 Formal Lab identifying unknown compound by jordanrichards » Mon Apr 21, 2014 5:26 pm
The purpose of this experiment was to separate and identify two compounds that were in unknown sample #109 by the process of fractional distillation. A series of tests allowed for us to identify physical properties of each compound as well as the functional groups present in each compound. They were boiling point test, refractive index test, ceric nitrate reagent test, chromic acid in acetone test, simons test for aliphatic amines and modified simons test for aromatic amines. The first compound which boiled out of the flask at 90oC was 2-butanol, which had a refractive index of 1.396, was soluble in water, had an IR peak for O-H and C-H at 3600-3200cm-1 and 3000-2800 cm-1 while also testing positive for OH group in the qualitative tests. The second compound, which boiled out of the flask at 163oC was 2-octanone, which had a refractive index of 1.415, was insoluble in water, had IR peak values for C-H and C=O at 3000-2800cm-1 and 1717.9cm-1 and came back negative for both tests indicating no O-H group and that the C=O was a ketone.

Figure 1: Chemical Structure of 2 separated compounds from this distillation experiment

Distillation is a method used to separate mixtures based on the volatile differences of their components in a boiling liquid mixture. In a closed container, equilibrium is reached from the molecules moving between liquid and vapour. When a molecule is in the vapour phase it exerts a pressure known as equilibrium vapour pressure. The magnitude of vapour pressure depends on the compound and temperature. Vapour pressure is a constant volume at specific temperature, as temperature increases so does the vapour pressure. The maximum pressure the vapour pressure can reach in an open container is the atmospheric pressure. This point is known as the normal boiling point and is the temperature at which vapour pressure reaches one atmosphere.3

A pure liquid can be distilled completely at a fixed temperature and that temperature will not change until the entire volume of liquid has transitioned from the liquid phase to the gas phase. The only problem is that, just cause the temperature remains constant, that does not mean the substance is pure.3

Miscible liquids on the other hand are liquids which can be dissolved into another liquid to form a solution. An ideal solution is a solution formed from components with no loss or gain of heat and the volume is the sum of the individual volumes. The total vapour pressure of an ideal solution is a function of the separate vapour pressures of components and their mole fractions. Raoults law states the partial vapour pressure is equal to its vapour pressure times its mole fraction.3

PA = PoA * NA and PB = PoB * NB

Boiling point is reached when P=Patm. The more volatile component A, will be more present in the vapour then in the liquid solution

mole Fraction AVapour/Bvapour > mole fraction ALiquid/BLiquid

In distillation, there will be more of the more volatile substance in the vapour phase compared to the less volatile which will remain mostly in the liquid phase.

Fractional Distillation in a fraction column can be used to separate substances when the vapour pressure of two components is very close and simple distillation is ineffective. When considering two liquids A and B in a solution, A having a lowering boiling point then B. They are in equilibrium with the vapour as the solution begins to boil. The vapour is richer in the more volatile component (ie. lower boiling point)

Figure 2: How pure component A is reached by using the boiling temperature of the other compounds

Azeotropic Distillation is when azeotropes distall without change in boiling point or composition even if the boiling points of components differ greatly. There are two types of azeotropes, a minimum boiling point mixture and a maximum boiling point mixture. Azeotropes can not…