Upload
cesar-ian-caermare
View
75
Download
0
Embed Size (px)
DESCRIPTION
Lab report; accuracy of paper not guaranteed
Citation preview
CHEM 142
Physical Chemistry I
Experiment 1
Liquid Density
September 07, 2012
Abstract
The purpose of this activity was to determine the densities of different salt solutions using
the pycnometer and hydrometer as a tool of determination. Appropriate statistical tools were
utilized to treat the data obtained in the laboratory. All statistical treatments were done at 90%
confidence level and the condition upon which the densities are obtained are at 300C. In the
analysis, it has been found out that the concentration of sea water is 3.4% m/v in terms of salt.
With a pooled standard deviation of ±0.004%m/v, the reliability of the result is acceptable. With
these, the experiment is a success.
Introduction
Density, ρ, is defined as the ratio of mass m of a substance to its volume, v. Because
volume expands with increasing temperature, density is thus greatly influenced by temperature.
In a liquid system, the number of particles present in the solution also affects density. When the
concentration is increased density is also increased.
Consequent to the above concept, we can solve for the concentration of a solution with
known analyte but unknown concentration using linear regression. In this paper, sea water salt
concentration will be analyzed. This can be done by obtaining the density of salt solutions with
known concentration for the linear regression plot, then plugging in the density of unknown salt
solution which is the seawater, then calculate for its density using appropriate variables.
Thus, this paper seeks to determine the concentration of unknown concentration of salt in
sea water by employing hydrometric and pycnometric determination method and provide
practice for chemistry major students in dealing with this type of analysis.
Methodology
A. Solution preparation
Salt solutions with concentrations of 0, 2, 4, 6, and 8 percent (g/mL) were prepared by dissolving
2 g NaCl(S) in 98 mL water for 2 percent salt solution, continuing using proportionality of NaCl-
water solution up to 8%.
B. Pycnometer determination method
Pre-boiled distilled water was used throughout the density determination of solutions. The
determination was carried out at 300C and at constant pressure condition.
a. Calibration of Pycnometer
Three 50 mL pycnometers were washed, dried, and cooled to room temperature. The
pycnometers were weighed to constant weight and then the weight was recorded as the weight of
pycnometer. . The pycnometer was then filled with distilled water and then the mass of water in
air was calculated from the difference of the mass of water in pycnometer and mass of
pycnometer. The actual volume of pycnometer was calculated from the mass of water in air. The
determination was done in triplicates. The actual volumes of individual pycnometers were
obtained using appropriate statistics.
b. Determination of Density of Salt Solutions
Calibrated pycnometers 1, 2, and 3 were filled with the prepared salt solutions and then
weighed. The weights were noted and the densities of individual solutions were calcultaed as a
function of their concentrations. A correction to vacuo was applied in the calculation for the
densities of solutions. The densities were calculated using appropriate statistical tools.
Unknown salt solution as sea water was analyzed for its density and then the density with
correction to vacuo and appropriate statistics was calculated.
C. Hydrometric Determination of Density of salt solutions.
A 100 mL graduated cylinder was filled with salt solution. A hydrometer was dipped in
the solution and the density was noted. The density was obtained and noted as a function of the
concentration of salt solution.
D. Treatment of Data
The mean densities of all salt solutions in pycnometric determination were compared
with the mean densities of the salt solutions in hydrometric concentration at 90% confidence
limit. The grand mean was obtained with the corresponding pooled standard deviations of salt
solutions. A calibration curve was constructed using the data obtained from standard salt
solutions, and then the concentration of salt in sea water was obtained by linear regression
equation using the obtained density of the salt solution.
Results and Discussion
Density determination was employed to calculate for the concentration of salt solution
with unknown concentration. Pycnometric and hydrometric determination of density was also
employed.
In pycnometric determination, three 50mL pycnometers were calibrated. Table 1 presents
the pertinent data in the calibration of pycnometers.
TABLE 1 Calibration of Pycnometer at 300C
Pycnometer Trial
WtH2O (g)
Density(g/mL)
Wt Corrected(g)
Volume Pycnometer(mL)
Meanvolume STDEV
1
1 50.6505 0.99565 50.59669 50.81775
51.09844 0.2430852 51.0699 0.99565 51.01564 51.238533 51.0704 0.99565 51.01614 51.23903
2
1 52.3564 0.99565 52.30078 52.52928
52.54503 0.0136442 52.3802 0.99565 52.32455 52.553163 52.3797 0.99565 52.32405 52.55266
3
1 51.5408 0.99565 51.48604 51.71099
51.69286 0.0156982 51.5137 0.99565 51.45897 51.68383 51.5137 0.99565 51.45897 51.6838
The actual volumes for the pycnometer were presented in table 1. As manifested, the
volume of pycnometer is not exactly 50mL. As such, calibration is really critical in this acitivity.
After the calibration, the densities of salt solutions were determined using the calibrated
pycnometers. Table 2 shows the densities of salt solution and sea water using pycnometric
determination.
TABLE 2 Densities of NaCl solutions and unknown as sea water
Results and Discussion
Table 2 presents the densities of salt solutions. From the densities of salt solutions with known concentration the concentration of NaCl in seawater can be estimated. The concentration of sea water as a salt solution will be calculated later on.
Hydrometric determination was also employed in the determination of densities. Table 3 shows the densities of salt solutions at 300C.
TABLE 3 Densities of Salt Solutions using Hydrometeric DeterminationDensity (g/mL)
%m/v salt trial 1 trial 2 trial 3 mean stdev0 0.995 0.995 0.995 0.995 N/A2 1.015 1.015 1.015 1.015 N/A4 1.02 1.02 1.02 1.02 N/A6 1.0418 1.045 1.04175 1.04285 0.0018628 1.04175 1.0583 1.05 1.050017 0.008275
sea water 1.0195 1.0233 1.021 1.021267 0.001914
Hydrometric and pycnometric determination of densities of substances show a slight deviation to each other due to apparatus limitations.
Appropriate statistical tools were utilized and it was found that at 90% confidence limit, both methods show no difference in the results. Thus, table two shows the calculation of grand mean for the densities of the solutions and the concentration of sea water in terms of NaCl was presented with linear regression equation y=0.0.996x + 0.0066.
TABLE 4 summarized densities of salt solutions and concentration of sea water% m/v pycno hydro Grand
meanSpooled
0 0.9945087
0.995 0.994754
0.003887
2 1.0087015
1.015 1.011851
0.002228
4 1.0211178
1.02 1.020559
0.003072
6 1.0361772
1.04285
1.039514
0.002228
8 1.0440617
1.050017
1.047039
0.006822
Concentration[seawater]
seawater
1.0159845
1.021267
1.018626
0.004384
3.4 % (m/v) NaCl
Table 4 can be better understood using the calibration plot illustrated by figure 1.
0 1 2 3 4 5 6 7 8 90.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
1.06
f(x) = 0.0066116241186107 x + 0.996296859493765R² = 0.983248634483759
Calibration plotLinear (Calibration plot)sea water
Concentration (%m/v)
Dens
ity (g
/mL)
Fig. 1 Calibration of salt solutions and the determination of concentration of unknown
Figure 1 illustrates the significance of linear regression to the determination of unknown with the construction of a calibration curve of known salt solutions. With 10% uncertainty, it can be concluded that sea water is 3.4% m/v salt.
Conclusion
In this paper, the concentration of sea water was analyzed in terms of %m/v NaCl. With
appropriate statistical tools, most reliable density from two methods was obtained, supplemented
by their pooled standard deviations.
At 90% confidence limit, the two methods show no difference in their results.
The density of the sea water being analyzed is not purely contributed by NaCl. Other
dissolved gases such as NH3 and O2 can also account for the density of sea water. Other
substances may still be present, since sea water is a real sample.
Even with these, the activity was very successful in providing the chemistry major
student to provide practice in the utilization of density of known salt concentrations to the
concentration of unknown salt solution with the use of Linear Regression method and/or
calibration construction method.
With these at hand, it can be concluded that the determination is a total success.