Identification of a Compound using Melting and Boiling Points
Introduction
One of the primary methods used to characterize a new
compound is the physical determination of its normal melting and boiling points.
The “normal” melting and boiling point is the temperature at which a
substance melts or boils when the barometric pressure is 760 mmHg or 1 atm.
In this experiment we will first calibrate our thermometers using ice and
water, whose normal melting and boiling points are well characterized as 0.0 °C
and 100.0 °C,
respectively.
Following this, we will measure the normal melting and boiling points of
an unknown compound. We will use this data to determine the identity of our
unknown from a list of possible unknown samples and physical data from the Chemical
Handbook.
Experimental
Procedure
As described in the lab
manual,
ice was placed in a beaker and warmed until approximately 50% had melted.
The temperature of the ice/water mixture was then measured with a
thermometer. This was followed by a similar measurement of our solid unknown.
In part II, water was heated until boiling and the temperature of the
liquid/gas mixture measured with a thermometer.
This was followed by a similar measurement using our unknown compound. To get the best results possible, the procedure in the manual
was modified by repeating each trial three times.
Data & Results
The Barometric pressure in the lab was
measured to be 761.2 mmHg.
Table One – Experimental Data
Trial
|
Water
Melting Pt.
|
Water
Boiling Pt.
|
Unknown 7
Melting Pt.
|
Unknown 7
Boiling Pt.
|
1
|
101.2 °C
|
80.2 °C
|
272.7 °C
|
|
2
|
0.1 °C
|
101.1 °C
|
80.7 °C
|
272.8 °C
|
3
|
0.0 °C
|
100.9 °C
|
80.4 °C
|
273.0 °C
|
4
|
0.1 °C
|
n/a
|
n/a
|
n/a
|
Averages:
|
0.15 °C
|
101.1 °C
|
80.4 °C
|
272.8
°C
|
Standard
deviation (s):
|
± 0.06
|
± 0.15
|
± 0.15
|
± 0.06
|
95%
confidence limits:
|
± 0.14
|
± 0.4
|
± 0.4
|
± 0.14
|
*
This trial was eliminated because the thermometer was broken (there was a bubble
of air in the mercury). A new
thermometer was obtained from the stockroom and used for all other data.
Observations: The unknown was yellowish-orange in color and had a fruity smell.
As can be seen from our water data the
experimental values for the melting and boiling points of water differed from
the theoretical values by +0.15 °C
and +1.1 °C,
respectively. These differences
were used to calibrate the average data for the unknown.
Thus the corrected values for the unknown boiling and melting points are
given in Table 2.
Table Two – Corrected Temperatures
Unknown 7
Melting Pt.
|
Unknown 7
Boiling Pt.
|
|
Measured value |
80.4 °C
±
0.4 (95%)
|
272.80 ± 0.14 °C
(95%)
|
Correction
|
+0.15 °C
|
+ 1.1 °C
|
Corrected
value
|
80.5 °C ±
0.4 (95%)
|
273.90 ±
0.14 °C
(95%)
|
These values were used to identify our
unknown. Table Three below lists
possible unknowns and the melting and boiling points for these compounds found
in the Chemical Handbook.2
Table Three – Reference Data from Chemical Handbook
Compound
|
Melting Point
|
Boiling Point
|
| Blabber Gas |
-15.8 °C
|
17.2 °C
|
Freezer Gel
|
82.7 °C
|
456.1 °C
|
Silly Putty
|
57.2 °C
|
121 °C
|
Billgatesium
|
1000 °C
|
unknown
|
Farsel Juice
|
80.8 °C
|
274.0 °C
|
Shampoo
|
-1.2 °C
|
108.7 °C
|
Based on these data we conclude that our
sample was probably “Farsel Juice” since both the melting and boiling points
fall within the confidence limits of our average melting and boiling points.
Additional evidence to support our conclusion is that Farsel Juice is
described in the Chemical Handbook
as having a yellowish-orange in color and has a “peach-like” smell.
Our unknown was this color and one of our group members observed a
“fruity” smell when she opened the bottle.
Although our measured
melting and boiling points differed from the theoretical data by a few percent,
this difference was very small leading us to believe that our results were quite
good. While there is still room for
error in our results due to the change in boiling and melting points as a
function of atmospheric pressure this difference should be very small.
Other factors such as contaminates in the water used may have affected
the results, but again every effort to minimalize such effects was made by using
only deionized water. Finally we did encounter some problems with our thermometer
in the first trial, but this was fixed by replacing it at the stockroom.
Thus our careful work, our additional color and smell observations, and
the fact that the corrected average of data exactly matched only one of the
choices with 95% confidence, all suggest that our unknown was in fact Farsel
Juice.
Conclusions
In this lab we determined the identity
of our unknown to be Farsel Juice using normal melting and boiling points.
A future experiment might include an additional calibration using the
barometric pressure and/or inclusion of other chemical properties such as
reactions of the compounds with acids and stuff to further test the nature of
the chemicals and more positively identify the chemicals.
Bibliograph
[1] Agenius, I.M., General
Chemistry for College, 2nd Ed., Overcharge Publishing House, Beverly
Hills California, 1999, page 12.
[2] Dr. Joe Scientist, Ed., Chemical
Handbook, 578th Ed., Big Chemical Press Inc., Bigtown, USA, 1999.
[3] Wizard, Mr., “Don’t
try this at home” – Experiments for General Chemistry, 1st Ed.,
Explosive Info Co., Ground Zero, 1978, Experiment 2, pp. 10-15.
13 komentar
please explain to me about data & results
BalasHapusThe data are the values written down as the experiment progresses,The results is usually in the form of a statement that explains or interprets the data. You do not go into any detail or explanations here. You simply say in words what your data is telling you
Hapuswhat is bibligraph? and why is importan?
BalasHapusWHAT'S A BIBLIOGRAPHY?
HapusA bibliography is a list of all of the sources you have used (whether referenced or not) in the process of researching your work. In general, a bibliography should include:
the authors' names
the titles of the works
the names and locations of the companies that published your copies of the sources
the dates your copies were published
the page numbers of your sources (if they are part of multi-source volumes)
OK, SO WHAT'S AN ANNOTATED BIBLIOGRAPHY?
An annotated bibliography is the same as a bibliography with one important difference: in an annotated bibliography, the bibliographic information is followed by a brief description of the content, quality, and usefulness of the source.
what is the conlusion of this report?
BalasHapusIn this lab we determined the identity of our unknown to be Farsel Juice using normal melting and boiling points. A future experiment might include an additional calibration using the barometric pressure and/or inclusion of other chemical properties such as reactions of the compounds with acids and stuff to further test the nature of the chemicals and more positively identify the chemicals.
HapusWhy on additional calibration using barometric pressure?
BalasHapusThe calibrated altitude maintains its accuracy as long as there are no significant changes in air pressure from certain outside conditions. Changes in weather are the most significant cause for changes in air pressure, but change in location can also affect the accuracy of the sensor as air pressure can vary from location to location.
HapusWhen experiencing a change in location or weather, consider recalibrating the sensor with the known elevation or correct pressure for best accuracy; refer to owner's manual for instructions on calibrating the altimeter.
Calibrating the sensor periodically when experiencing changes in air pressure will ensure the highest level of accuracy.
what is barometric pressure?
BalasHapusAtmospheric pressure, sometimes also called barometric pressure, is the pressure within the atmosphere of Earth (or that of another planet). In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. Pressure measures force per unit area, with SI units of pascals (1 Pa = 1 N/m2). On average, a column of air one square centimetre [cm2] (0.16 sq in) in cross-section, measured from sea level to the top of the Earth's atmosphere, has a mass of about 1.03 kilograms (2.3 lb) and weight of about 10.1 newtons (2.3 lbf). That weight (across one square centimeter) is a pressure of 10.1 N/cm2 or 101 kN/m2 (kPa). A column 1 square inch (6.5 cm2) in cross-section would have a weight of about 14.7 lb (6.7 kg) or about 65.4 N.
Hapusplese explain to me, how to get a conclusion?
BalasHapusA conclusion should
Hapusstress the importance of the thesis statement,
give the essay a sense of completeness, and
leave a final impression on the reader.
Suggestions
Answer the question "So What?"
Show your readers why this paper was important. Show them that your paper was meaningful and useful.
Synthesize, don't summarize
Don't simply repeat things that were in your paper. They have read it. Show them how the points you made and the support and examples you used were not random, but fit together.
Redirect your readers
Give your reader something to think about, perhaps a way to use your paper in the "real" world. If your introduction went from general to specific, make your conclusion go from specific to general. Think globally.
Create a new meaning
You don't have to give new information to create a new meaning. By demonstrating how your ideas work together, you can create a new picture. Often the sum of the paper is worth more than its parts.
Can be water make an error result for boiling point?
BalasHapus