Chem II – Lab report comparisons
The following are snippets from the lab reports of your classmates (maybe some of your report is in
here!). These are good examples of how a report should be written, but not necessarily perfect! There
may still be some typo’s or mistakes present. Take a look at these and compare them to your work.
Realize that the snippets may be an entire section (full introduction, etc.) or just a small bit of a section
(a sentence from the conclusion, etc.)
Happy lab reporting!!
Introduction
Sample 1:
In this lab spectroscopy is utilized to study different samples of ethanol. Spectroscopy is the shining of
light through a sample and collecting the amount of light that has passed through the sample. This
process produces the percent transmittance which is used to calculate the absorbance of light through
the object. Students will be measuring the amount of light absorbed and transmitted through an
ethanol solution using a spectrophotometer. The purpose of this lab is to use spectroscopy to identify
an unknown concentration of ethanol in an ethanol solution by comparing it with unknown
concentrations on a calibration chart. When this data is put onto the chart, the unknown ethanol
concentration can be found.
Sample 2:
In chemistry, there are many ways to observe and learn more about samples of different chemicals.
One of these ways is spectroscopy. Spectroscopy is using light as a tool to measure how much energy
a sample absorbs. To use spectroscopy, light is shone through a sample, and the absorbance can be
found by how much light is transmitted. In this lab, spectroscopy was used to find the absorbance
measurements of different concentrations of Ethanol, and solve for the unknown ethanol concentration
used in the lab.
Procedure
Sample 1:
Each flask then had a different ethanol solution added to the solution (needs to add how much). The
ethanol solutions were as follows: 0%, 2.5%, 5% and 10%. After five minutes had passed, 39 mL of
water were added to each flask and swirled.
Sample 2:
After the reaction, exactly 39.0 mL of distilled water was (were) added to each flask and swirled.
Then, cuvettes were labeled numbers one through four and filled two-thirds full with the solution from
the corresponding flask. After each cuvette was filled, they were placed in a spectrophotometer set at
560 nm. Transmittance of 100% was set for the blank cuvette. The absorbance and transmittance
measures were recorded for each (sample). The blank cuvette was recorded between each recording to
assure the spectrophotometer’s accuracy.
Conclusion
Sample 1:
With this, a calibration plot was created to show the relationship between concentration and
absorbance of Ethanol solutions. Displayed on the scatter plot above is the direct relationship between
concentration and absorbance. As the percent concentration increases, so does the absorbance value.
Solutions with varying concentrations of Ethanol were used to find the concentration of an unknown
sample of Ethanol. The results from the lab showed that adding a higher concentration of Ethanol to a
solution blocked more light than a lower concentration of Ethanol.
Sample 2:
… then the results would have been changed. There would have been more Ethanol in the solution, so
more light would have been absorbed, changing the absorbance and messing up the graph.
Sample 3:
Using spectroscopy to find an unknown was the main purpose of this lab. The spectrophotometer was
fairly accurate when it measured the different concentrations of ethanol. This is true because the “r
squared” value was .93, which indicates that the trend line is pretty good.
Sample 4:
The unknown was number four and was found to have a 15.7% concentration of ethanol.
Sample 5:
In conclusion, the lab’s purpose was fulfilled. The concentration of unknown (II) was found the be
1.43% ethanol. Using spectroscopy to find the transmittance and absorbance levels of various
concentrations of ethanol, the unknown concentration was able to be calculated.