Separation of a Mixture
By Justin Wright
Portland Community College
General Chemistry I
11/2/2012
Abstract
An unknown mixture containing Fe, NH4Cl, SiO2, and NaCl was obtained and the
percentage composition for each component was to be identified. A separation scheme
was devised to separate the four known components using magnetism, sublimation,
filtration, and evaporation. The experimental results indicate that the unknown mixture
was 15.4% Fe, 15.3% NH4Cl, 49.70% SiO2, and 18.5% NaCl.
Introduction
In nature, matter usually occurs in the form of a mixture (1). Therefore it is important to
be able to separate mixtures into their individual components in order to better study
them. There are many ways to separate mixtures by taking advantage of the unique
physical properties of each component in a mixture. A few common techniques include
magnetism, distillation, and filtration.
Since separation techniques take advantage of the variations in physical properties, the
best way to devise a separation scheme is to become familiar with the physical properties
of each individual component. Once the physical properties for each component are
known, specific separation techniques can be selected that take advantage of the unique
characteristics of the various components. For example, in this particular experiment, it
was known that one of the components of the mixture was ammonium chloride. A unique
characteristic of ammonium chloride is that it sublimates at 338 degrees Celsius,
therefore this technique was used in the experimental process to isolate the ammonium
chloride from the other components of the mixture (2). Other separation techniques were
then added to the separation scheme to isolate the remaining components of the mixture.
Experimental Methods
The first step of the experiment was to obtain the mass of the unknown mixture. An
empty beaker was weighed using a scale and the unknown mixture was then added to the
beaker and weighed again. The final weight was subtracted from the initial weight of the
empty beaker to attain the mass of the unknown sample.
Next, the iron was separated from the mixture via magnetism. A small magnet covered in
plastic wrap was placed in the beaker, which attracted the iron from the remaining
components of the mixture. The beaker containing the remaining three components of the
mixture was weighed on the scale. The mass of Fe in the mixture was then obtained by
subtracting the measurement from the measurement recorded in the previous step.
The next step of the separation scheme was to remove the ammonium chloride via
sublimation. The beaker containing the three remaining components was heated over a
Bunsen burner inside a fume hood. The mixture was then removed from the heat once no
more gas was visible. After cooling to room temperature, the beaker was weighed on the
scale. The mass of ammonium chloride was calculated by subtracting the measurement
from the previously recorded mass measurement.
2 To separate the silicon dioxide, approximately 10 mL of deionized water was measured
in a graduated cylinder and added to the mixture. A piece of filter paper was weighed on
the scale and then formed into a cone. An empty beaker was also weighed on the scale
and the mass was recorded. The mixture was then poured into the empty beaker through a
funnel containing the filter paper and the silicon dioxide was separated via filtration. The
filter paper containing the sand was placed in the oven to dry. After the sand was
completely dry, it was then weighed with the filter paper and the mass of silicon dioxide
was obtained by subtracting the previously recorded mass of the filter paper.
Heating the remaining salt-water solution on a hot plate until all the water evaporated
isolated the final component, salt. The beaker was weighed and the total mass of salt was
obtained by subtracting the initial beaker measurement from the beaker and salt
measurement.
Results
The devised separation scheme effectively separated the unknown mixture into its
individual components. The experimental results indicated that sand was the primary
component of the mixture, which accounted for 49.70% of the total mass of the mixture.
The experimental results and known composition percentages for each component in the
mixture are displayed in Table 1 below:
Table 1: Experimental Results
Substance
Unknown #5
Fe
NH4Cl
SiO2
NaCl
Mass of Substance
± 0.001 (g)
3.012
0.463
0.460
1.497
0.558
% Composition
(Experimental)
15.4
15.3
49.70
18.5
% Composition
(Known)
15
15
50
20
% Error
2.7
2.0
0.60
7.5
The following equations were used to calculate the percent composition and percent error
values for each substance:
𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝐶𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑖𝑜𝑛 = 𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑒𝑟𝑟𝑜𝑟 = 𝑀𝑎𝑠𝑠 𝑜𝑓 𝐼𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙 𝐶𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡
× 100
𝑇𝑜𝑡𝑎𝑙 𝑀𝑎𝑠𝑠 𝑜𝑓 𝑆𝑎𝑚𝑝𝑙𝑒 𝐸𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 – 𝐴𝑐𝑡𝑢𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 × 100
𝐴𝑐𝑡𝑢𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 As seen in Table 1 above, an acceptable percent error of less than 5% was achieved for
Fe, NH4Cl, and SiO2. The experimental percent composition obtained for NaCl was
inaccurate due to a percent error of more than 5%.
3 Discussion
There were a few limitations and possible sources of error during the experimental
process. Each of these items may have had an impact on the accuracy of the experimental
results.
While removing the Fe from the mixture via magnetism, a few grains of sand and/or salt
were mixed in with the iron on the magnet. Special care was taken to remove the sand
and/or salt from the magnet, but it was not possible to remove every noticeable grain.
During the sublimation process, a white gas was released and formed a residue on the
side of the beaker. Each side of the glass was held over the flame until the white residue
was completely gone to ensure that all of the ammonium chloride was removed from the
mixture. A small amount of red residue was also found on the side of the beaker and
could not be removed.
Another possible source of error occurred during the filtration phase. A small tear was
discovered in the filter paper when transporting the sand to the oven. The tear was
noticeably bigger after being subjected to the heat of the oven. Special care was taken to
ensure that no sand was lost as a result of the tear.
Conclusion
The results of the experiment indicate that the mixture was 15.4% Fe, 15.3% NH4Cl,
49.70% SiO2, and 18.5% NaCl. The respective percent errors for each individual
component were 0%, 0%, 0%, and 0%.
References
1. Silberberg, Martin S. 2012. Chemistry: The Molecular Nature of Matter and
Change, 6th Edition. The McGraw-Hill Companies, United States of America.
2. Haynes, W. M. 2011. CRC Handbook of Chemistry and Physics – 92nd Edition. CRC
Press, United States of America.
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