Chemistry

1. Each answer needs to be specific and include examples from experiment 8

How spectrophotometers work
A regular spectrophotometer contains a light source that emits the spectrum of visible light, or sometimes even specific wavelengthscolors of the visible spectrum, onto a material (spectrometer). As the light gets absorbed by, transmitted though, or scattered by the material the spectrophotometer also contains a detector that detects either the scatteredreflected light or the transmitted light (photometer). The spectrophotometer used in experiment 8 measures the light transmitted through an object. The output data is usually in the form of a histogram of the intensity of light vs. the wavelength (which represents the different colors). The spectrophotometer in experiment 8 outputs a graph of transmittance vs. the wavelength. Percent transmittance is the ratio of the measured transmitted light to the emitted light but this is ideally first calibrated by measuring 100 which is the unhindered light source and 0 which is no light source and which just measures the background light. From the percent transmittance of a material, one is also able to determine its absorbance. the kinds of information spectrophotometers can provide to chemists.

For a light source that emits the full visible spectrum, the wavelengths of course correspond to particular colors thus the spectrophotometer can reveal which colors the materials transmit, scatter, or absorb. When one is able to see the material though, this does not seem like such important information, but it does provide some information about other important characteristics of the material. The way a certain material refracts or reflects light is inherent in its chemical structure. This can be traced down to the vibrational characteristics of the molecules, the electronic structure of the compound, etc. And while this usually manifests in its physical appearance, there are some material-light interactions that are not easily detectable by the human eye, that is why sensitive instruments like the spectrophotometer are needed these give quantitative data for analysis to supplement the qualitative data from simply inspecting a material. Especially when one uses a spectrophotometer that uses a light source that emits to the near-ultraviolet and near-infrared, this gives more information since certain materials react to these wavelengths in certain ways. Other information one can derive from spectrophotometer data is the concentration of certain solutions (Beer-Lambert Law) and consequently other details related to chemical kinetics (rate constants, storage life, etc.).

Predict the colors you expect your eye to see when looking at the two compounds represented by the blue line and the yellow line in the graph above. EXPLAIN YOUR ANSWER.

Blue Line The line rises around the wavelengths 600-700 nm, and 400nm these correspond to yellow, orange, red, and then violet respectively. Judging from the heights of the peak, it is highest at the wavelength of red so we can predict this to be the dominant color that reaches ones eye. Although, since violet, yellow, and orange are also transmitted it might be a distinctly dark shade of red. The peaks of a  Transmittance vs Wavelength graph usually correspond to the wavelengths of the colors that the naked eyes sees a material to be.Yellow line

Judging from the distinct rise in the line around the wavelengths of blue and greens light, this should be a greenish blue material. This is because it scatters or absorbs all other wavelengths of light except blue light and green light and some of the wavelengths near them, so these remaining wavelengths are the dominant bands that reach the eye. Since it has a slightly higher peak at 500 (blue) than 550 (green) though, one can assume that it is slightly more blue than green, thus the prediction of greenish blue.

as a result of this experience, what have you learned about the role of technology in science
Technology is vital to the progress of science. It is said that technology comes before science, that people make things that work out of necessity (technology) before wondering how or why they work (science) but I believe that it is a cycle. As technology becomes more advanced, it needs science to keep it growing and as science becomes more complex, it needs technology to give it the tools to keep up with and expand its complexity. People see colors everyday, many of them appreciate it, but not too many of them put too much thought into the science behind it. It is interesting to know that through the technology of spectrophotometry, for example, such a simple everyday idea such as the colors of objects can be a source of complex knowledge. Technology helps us take closer looks at things, in a way, to get information from them that have so many different uses. As we gain this new knowledge, we can apply it to improve our existing technology, or once we reach what seems to be a dead end in our information-gathering we work hard to improve our technology to overcome it, and with this new technology we can learn even more things that we can apply again to progress, and so on and so the cycle goes.

Some information

EMPLOYING TECHNOLOGY AND LIGHT

Any sufficiently advanced technology is indistinguishable from magic.

Technology has added immeasurably to our ability to analyze and understand our world.  Unfortunately, the essence of what these tools do for us is often hidden under the cover and inside the circuits contained within.  To try to avoid the magic issue (or black box) Mr. Clarke alludes to above, we will use an instrument that is simpler than most and use it to try to get an understanding of what it is doing and how it gives us information our unaided hands and eyes cannot give us.

What our eyes see is the result of white light hitting objects.  The object reflects some of that light to our eyes, nerves then send signals to the brain, and the brain interprets those nerve signals in terms of shapes and colors.  White light is composed of all the colors, so if the object you see is red, for example, it is because the object is reflecting the red component of white light back to your eyes and absorbing the other colors.

Using technology, we can shine just one color of light at a time through a transparent material. Since the material is transparent, light that is not absorbed by the material will be transmitted through the material and is detectable on the other side.  When we do this, the instrument collects very specific information about which colors of light and how much of the light is transmitted through the material.  This information can be used to further classify and characterize that material beyond the information our eyes are able to give us.

Light is a wave phenomenon, but visible light is not the only thing that is composed of waves.  There are radio waves, microwaves, and ultraviolet waves to name only a few, and each type can be used to give us different kinds of information about substances when we bombard those substances with those waves.  We will not have time to explore the variety of technology associated with waves, but the experience in this lab will provide some insight into how these instruments work.  Probably the most interesting instrument that functions on the principles explored in this lab is MRI (Magnetic Resonance Imaging), a very widely used medical tool.

Technology has allowed us to expand our chemical knowledge by allowing us to see things our eyes cannot and measure things our hands cannot.  Technology has provided additional tools for expanding our chemical knowledge.

We will explore the use of technology and light with a very simple tool, the Spec 20.  This instrument has a light source that produces waves in the visible and ultra-violet portion of the electromagnetic spectrum.  We will use only the visible spectrum in this exercise.  Any material that appears colored to our eyes will display a distinctive fingerprint when we graph how much of each different color of white light is transmitted through the sample.

We will create these fingerprints for several of our Experiment 2 solids.  The instrument we are using is designed to use liquid samples, so we will need to use a clear colorless liquid to dissolve our samples in order to study them.  Water will be our clear, colorless liquid of choice.

PROCEDURES
Procedure 1 will give us a visible reference for what color of light is associated with the numerical scale on the instrument.  Next, we will need to decide which of our solids can be studied using this instrument and assign those solids to groups.  During Procedure 2, will we prepare the solutions for data collection and set up an Excel worksheet to record and display our data.  Procedure 4 will then be divided up between the groups.
 
PROCEDURE 1  DEMYSTIFYING THE INSTRUMENT
Instead of speaking in terms of the color of the light, chemists refer to light in terms of a measurement called wavelength.  The first thing we need to do is take a simple look at how the instrument works and then connect the colors of visible light with the wavelength.

PROCEDURE 2  PREPARING THE SOLUTION AND DATA DISPLAY
In order to get the full scope of information from the instrument, the solutions we are studying need to be within an acceptable concentration range.  Directions will be given for how to accomplish this.  We will also set up an Excel spread sheet to record and display our data.

PROCEDURE 3  COLLECTING THE FINGERPRINT (QUALITATIVE)
A significant application of technology of this type is creating a fingerprint of a substance in order to identify it.  We will compare the computer generated (Excel spreadsheet) graphs of the collected data to see what these fingerprints look like.

Report Sheet Directions

From report sheet
Import the two Excel graphs of Absorbance vs. wavelength into Word and then answer the two questions.
Color Spectrum400425450475500525550575600625650675700VioletVioletBlueBlueGreenGreenGreenYellowOrangeRedRedRedRed

Using the graphs of your two samples, explain which color(s) of light are most strongly absorbed by each compound and how you know that. (This requires one answer for each graph.)
Blue Vitriol The colors absorbed by Blue Vitriol correspond to the wavelengths where the spectral line begins to dip in the graph. Specifically these are yellow, orange, and red it also absorbs some violet, but not as much as the other three. Judging from the lowest values of  transmittance, of the absorbed colors, it absorbs the color red the strongest. For a substance like blue vitriol, absorbance corresponds to roughly the inverse of its transmittance, disregarding reflectance and scattering. This is why the dips in transmittance indicate the absorbed colors and the lower the value of transmittance, the higher the possible value of absorbance.

Retgersite  The colors of light that Retgersite seems to absorb are mostly green (550nm), and some blue and yellow. As mentioned before, the dips in the transmittance vs wavelength graph correspond to the absorbed colors and the dip in the wavelength of green is very distinct in this graph. Although, this can also be attributed to the scattering of that particular color by the material.

How can looking at these graphs allow you to predict the actual color of the compound without having to see the compound itself
We can use our graphs to predict the actual color of a compound (without seeing the compound) by looking at our percent transmitted at certain wavelengths and look at the color spectrum table and match that wavelength from the graph. For Transmittance vs. Wavelength graphs, the peaks correspond to the wavelengths of the actual colors of the materialobject. Meanwhile, for Absorbance vs Wavelength graphs, the dips (troughs) correspond to the wavelengths of the actual colors of the material.