Identifying Three Unknowns Organic Chemistry Formal Lab

Introduction

In this lab, we were attempting to separate the individual components from a three component unknown solution. With knowledge of different methods of separation, we will be able to differentiate the three distinct components to our mixture. Once the chemicals in our solution have been properly separated, we will use an infrared spectrometer to identify the specific components that made up the unknown given to us.

In order to begin this lab procedure we first had to find all of the specific melting points, boiling points, and solubility of the possible unknowns that could make up our solution. The possible unknowns that were given to us were methanol, ethanol, acetone, isopropyl alcohol, isopentyl alcohol, octyl alcohol, ethyl ether, water, caffeine, sucrose, dextrose, acetylsalicylic acid, and cholesterol.

Table 1 (below) shows the potential unknowns our solution was composed of and their respective melting points, boiling points, and solubility.

Table 1. Properties of Unknown Chemicals

Unknown Chemicals Melting Point Boiling Point Solubility

Methanol -98 ℃ 64.6 ℃ Polar

Ethanol -117 ℃ 78.5 ℃ Polar

Acetone -95 ℃ 56.2 ℃ Polar

Isopropyl Alcohol -89 ℃ 82 ℃ Polar

Isopentyl Alcohol -117 ℃ 130 ℃ Non-Polar

Octyl Alcohol -16 ℃ 194 ℃ Non-Polar

Ethyl Ether -116 ℃ 34.5 ℃ Non-Polar

Water 0 ℃ 100 ℃ Polar

Caffeine 238 ℃ 178 ℃ Polar

Sucrose 186 ℃ --- Polar

Dextrose 146 ℃ --- Polar

Acetylsalicylic Acid 135 ℃ 140 ℃ Non-Polar

Cholesterol 148.5 ℃ 360 ℃ Non-Polar

(PubChem, 2012) (ChemSpider, 2012)

It was necessary to obtain the boiling points of these substances because when performing a distillation, which is one of the methods of separation used in this lab, we are able to find the distinct boiling points of certain chemicals. The boiling points that are found in the distillation process are then compared to the standard boiling points that were stated in Table 1. In order to identify a solid that could be present in our unknown solution it is necessary to have the melting points of all of the possible unknowns. If a solid is visibly present in your solution, or if one appears during a distillation you can isolate in and then put it in a MELTEMP machine to determine the melting point of the solid, which will then be compared to the standards. With the knowledge that a polar solution will not dissolve a non-polar solution, we know that if a separation line is present there is a difference in polarities in our unknowns. With prior understanding of which of our potential unknowns are polar or non-polar we will be able to narrow down the list of possible substances that are making up our solution.

In performing this lab, we believe that using one or more methods of separation we will be able to identify each of the three separate components to our solution. The potential methods of separation that could be used to identify our unknowns are the process of distillation, filtration, and liquid-liquid extraction. Based on the appearance of your liquid, you will know which of these methods to begin with.

If there is a solid apparent in your solution, you should begin with a filtration. Filtration is the process of separating suspended solid matter from a liquid, by causing the latter to pass through the pores of some substance, called a filter (Lenntech, 2009). For this lab, we will use a vacuum filtration. Adding a vacuum to the filtration will simply help to make the solid filter out faster.

If a separation line is visible, then you should perform a liquid-liquid extraction. We know the separation line is there because one of the substances in the unknown has a different polarity than the other two. Liquid-liquid extraction is based on the transfer of a solute substance from one liquid phase into another liquid phase according to the solubility (University of Alberta, 2010). This type of extraction is performed using a separatory funnel.

If there is no apparent separation line or a visible solid, then you should proceed with a distillation. Distillation is the process of heating a liquid until it boils, and then condensing and collecting the resultant hot vapors (University of Colorado at Boulder, 2013). For our distillation we used a Wes condenser apparatus in order to condense the vapors and collect them.

Once you believe that the three components to your unknown are separate, then you can proceed with using the infrared spectrometer. It is wise to use the IR to identify your unknowns instead of just relying on the boiling points and melting points of the components considering that what you obtained may not be a pure substance. This machine uses a device called a chopper to produce infrared light, which then shines through the sample of each of the three unknowns you isolated. It will then bounce off a series of mirrors until it reaches the detector. The detector will determine the wavelength at which the molecules of the substance are vibrating and it will produce a graph of light intensity vs wavelength. You can then compare this graph with a graph of the standards in order to determine if the substance you predicted you had from the boiling and melting points of the components is really the substance that you have.

I worked in a group with Rachael Hager and we received vial #1. The unknown in our vial neither showed an apparent separation line or a solid, so we chose to proceed with distillation.

Methods

Figure 1. Schematic of Plan to Separate Unknowns

Figure 1 shows the multiple ways that the three component unknown could have been separated, depending on what made up the mixture. The pathway that we took is highlighted.

My group received vial #1, since there was no apparent solids or a separation line, we proceeded with a distillation. To perform a distillation three ring stands will be needed. On the first ring stand, attach a clamp with a round-bottomed flask. In this flask should be your unknown. Attach a three-way glass piece to the top of the round-bottomed flask, and cork the top part of the glass piece with a cork that has a small hole. Inside this small hole,