Chemistry

Image of molecule from csus.edu
Image edited by Lap

Chromatography

Chromatography is a method in which a mixture is separated into components between two phases. This allows analysis of the sample and the chemical reaction. The two phases are stationary and mobile phases. The stationary phase remains in place, while the mobile phase carries the components through the medium. The components of the mixture move in different speeds based on their solubility and affinity to the stationary phase.

Thin layer chromatography

One way to separate the mixture for analysis is thin layer chromatography (TLC). TLC has a layer of silica gel (stationary phase), which acts as an absorbent because of its large surface area for interacting of molecules, over a plate of plastic. Silica gel has a very polar surface because of the –OH bond, which can form hydrogen bonds, van der waals, and dipole-dipole interactions. Mixtures or compounds are blotted into the TLC plate and a solvent (mobile phase) is added. As the solvent travels up the plate due to capillary force, the compound will move up by constantly absorbing to the surface and dissolve back to the solvent. Due to the compounds’ different polarities, they will travel up at different rates. The more polar the compound is, the more affinity it has for the stationary phase and will travel less distant than a less polar compound. 

Column Chromatography

Another method is column chromatography, which works in a similar way but mixture can be completely separated into components. Instead of using a TLC plate, a column filled with silica gel is used. The less polar compounds travel down faster than a more polar compound. Therefore, a less polar solvent is used at first, then a more polar solvent is used for later fractions to get the more polar compounds out.

Gas chromatography

Gas chromatography is another method to analyze samples by separation. Gas chromatography separates the components by volatility and the molecules travel through a column with the help of helium. Higher volatility travels faster than low volatility components.

High performance liquid chromatography

Last is the liquid chromatography and the high performance liquid chromatography (HPLC). HPLC consist of a pump that moves the mobile phase and mixture through the column and a detector that analyzes the sample, such as spectroscopy. 

Using these methods, a sample mixture can be separated into individual components in which we could identify, quantify, and purify. 

Technology in Chemistry Education

Many educators have shifted from using the blackboard to using powerpoints and overhead projectors, while some still uses blackboards to teach. In my experience, it is usually harder for me to follow the professor when he/she uses the blackboard, since the professor talks and writes at the same time. Students usually want to get down every bit of information that the professor gives out, whether it's verbal or written. This is why powerpoints are an effective tool in teaching, provided that the professor does not read out the powerpoint. Another solution would be providing audio or video podcast so students can review the materials they might have missed. Videos would also be very helpful in chemistry or other science labs. It can be used to demonstrate lab techniques or how to operate different instruments. I think this would be a lot more effective in preparing students before performing the experiment.

Many employers have stated that they prefer job applicants to have in-depth knowledge of basic chemistry theories and creative thinking than to have the understanding of technology used in labs, which can be obsolete in a few years. But job listings specified that the knowledge of many different technologies used in labs are required. I believe schools should put a bit more focus on practical skills and to be more technology oriented to accommodate the needs of the industry.

How does a refractometer work?

The refractometer can be used to measure the salinity and specific gravity of water, plasma protein in blood sample, and specific gravity of urine. A refractometer measures the refractive index of a sample. The refractive index is the ratio of the speed of light traveling in a vacuum to the speed of light traveling in the sample. The refractometer utilizes the physics of light to find the refractive index of the liquid, since light bends when passing through one medium to another, in this case, the liquid sample to the prism. How the light bends is proportional to the refractive index of the sample and the refractive index of the sample can be read on the scale of the refractomenter. The salinity of the sample can be calculated from the salinity vs. refractive index plot (y=5585.5x-7446.2). Based on Frank J. Millero and Alain Poisson’s measurements, the density as a function of salinity and temperature was derived (at 1atm). The equation is the following: ρ= ρ0 + AS + B(S^3/2) + CS, where A, B, and C are functions of temperature, S is the salinity, and ρ0 is the density of water.

Most of the time, an Abbe refractometer is used to measure the refractive index. Alternatively, the refractive index can also be measured by using diffraction grating. Note that this apparatus can be made by yourself with materials such as a diffraction grating, laser pointer, transparent tray, clips for hanging cloth, tracing paper, and tape. Here is the link for how to measure the refractive index using this method: http://www.pl.euhou.net/docupload/files/Excersises/WorldAroundUs/IndexOfRefraction/IndexOfRefraction.pdf