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Chromatography and Ionic versus Covalent Bonds

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15.1.3 CIA Demonstration: Chromatography

After you watch the above video, answer the questions below in sufficient detail:

(a) (3 pts.) This video discusses 3 different types of chromatography. List each one mentioned, and describe their differences in as much detail as possible (your points earned will be proportional to the level of detail in your discussion). Which one was used in this lab demonstration?

Answer: Gas chromatography (GC) – utilized by scientists in order to be able to separate the volatile particles of a mixture. This is done with the aid of a syringe where the sample is drawn and then transferred to the port of the gas chromatograph called the into injector port. It is then set to reach a very high temperature which exceeds the appropriate boiling point for the substances, thus, allowing the particles to evaporate. Then helium is introduced in order to facilitate the flow the evaporated substances to the gas chromatograph column where the separation will then take place (www.gas-chromatography.net).

High performance (or high pressure) liquid chromatography (HPLC) – is an effective type of column chromatography which is widely used in pharmaceuticals. It is very useful to determine the assay and related substances in drug substances. In general HPLC is used to separate the components of a mixed drug substance. In HPLC chromatography, column plays a significant role in separation of different compounds because it contains stationary phase. Stationary phase is a bad of polar or nonpolar particles according to the type of column. Polar and nonpolar columns are used according to the nature of the sample to be analyzed (http://www.pharmaguideline.com/2013/07/principle-of-hplc-liquid-chromatography.html).

Thin layer chromatography (TLC) was used in the lab demonstration. TLC is a simple, quick, and inexpensive procedure that gives the chemist a quick answer as to how many components are in a mixture. TLC is also used to support the identity of a compound in a mixture when the Rf of a compound is compare with the Rf of a known compound (preferably both run on the same TLC plate). A TLC plate is a sheet of glass, metal, or plastic which is coated with a thin layer of a solid adsorbent (usually silica or alumina). A small amount of the mixture to be analyzed is spotted near the bottom of this plate. The TLC plate is then placed in a shallow pool of a solvent in a developing chamber so that only the very bottom of the plate is in the liquid. This liquid, or the eluent, is the mobile phase, and it slowly rise up the TLC plate by capillary action (http://orgchem.colorado.edu/Technique/Procedures/TLC/TLC.html).

(b) (2 pts.) How did chromatography get its name, and how is it used differently now compared to in the past (according to the video)? Give an example. What is chromatography, and how exactly does it work?

Answer: The name chromatography is used because the techniques were originally developed to separate colored compounds (chroma = color). However, modern chromatography allows for the separation of compounds based on their properties. Chromatography is a method for separating the parts of a mixture of either a gas or liquid solution containing different chemicals. For example, pen inks are often made up of different colors. The different bonding properties of each molecule type are exploited. Chromatography is used in both qualitative and quantitative analysis of both organic and inorganic samples.

This technique uses two types of substances: 1. Mobile phase: a gas or liquid that transports the solution being tested through the other substance (water, rubbing alcohol are examples). 2. Stationary phase: the liquid or solid through which the tested substance is carried (coffee filter paper, paper towel are examples). It is necessary for the different chemicals in the solution fo have different properties such as molecule size or a different ability to dissolve in a solvent. The stationary phase will absorb or slow down different components of the tested solution to different degrees creating layers as the components of the solution are separated. Chromatography was invented by the Russian botanist, Mikhail Tsvet. Chemists use this process to identify unknown substances by separating them into the different molecules that make them up.

(c) Suppose I melted a grape (purple) popsicle and ran a chromatogram of the resulting substrate. [i] (1 pts.) In the simplist case, what would I expect to see? Include as much detail as possible.

Answer: Once the chromatogram has been completed and is ready to be measured and calculated, on the plate that was used to perform the chromatogram you should see where the red and blue have completely separated. The red food coloring dye should be lower on the plate than the blue food coloring dye.
Rf = .36
Shortest wave length color: Rf = 36mm/57mm
Rf = .63

[iii] (2 pts.) What does this mean? Why, in this case, would one component of the sample travel farther than the other? What’s going on here—what causes this to happen? Be specific and detailed to receive credit.

Answer: The molecules that make up the components of the sample have different polarities, and what we are witnessing is a competition between the affinity of the dye for the stationary phase, which is the piece of paper, and the mobile phase, which is the water. Both water and the paper are polar and depending on how well the particular component sticks to the paper versus wanting to move along with the water, determines the fact that we get different Rf for the two compounds.

(d) (2 pts) What is the difference between the stationary phase and the mobile phase as it relates to this lab? What was the stationary phase in this demonstration? What was the mobile phase in this demonstration? You must be specific to receive credit.

Answer: stationary phase – the moving support on which chromatography is performed; can be a solid or liquid, depending on the type of chromatography

Mobile phase – the moving phase that carries the mixture in chromatography; can be a liquid or gas, depending on the type of chromatography

In the lab, the filter paper was the stationary phase and the water was the mobile phase.


Please watch the following Thinkwell video:

8.1.1 CIA Demonstration: Conductivity Apparatus-Ionic versus Covalent Bonds

After you watch the above video, answer the questions below in sufficient detail:

(a) (1 pts.) Please state in the blanks provided whether the following samples from the lab were an electrolyte or a nonelectrolyte:

Pure water nonelectrolyte Drain cleaner: electrolyte

Ethanol: nonelectrolyteSucrose: nonelectrolyte

Sodium chloride: electrolyte

(b) (2 pts.) Explain your answers to (a) above detail according to what you witnessed in this lab demonstration. What is the evidence for each? How did you arrive at your answers? What does the type of chemical bond have to do with this? Be specific.


(c) (3 pts.) If you have ever been to a public pool, you know that you are required to exit the pool when there is lightning in the sky. But consider your results from part (a) above and what you learned in this lab, paying particular attention to the very first demonstration that the instructor shows you regarding the light bulb. Does this protocol make sense in light of the data from this demonstration, or is it contradictory? Why or why not? We are talking about water, here, right? Is there anything else going on in this case, chemically speaking, that would change the way we look at this situation?



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