Selina Rabin S. Gualberto Selina Rabin S. Gualberto
Group 2 Sec. I – 2L Group 2 Sec. I – 2L August 1, 2012 August 1, 2012 _____________________ _____________________ 1 1
A scientific paper submitted in partial fulfillment of the requirements in General A scientific paper submitted in partial fulfillment of the requirements in General Biology I under Prof. Kevin Labrador, 1st sem., 2012-2013.
ABSTRACT ABSTRACT
The effect of molecular weight on the diffusion rate The effect of molecular weight on the diffusion rate of substances was determined using the glass tube test and of substances was determined using the glass tube test and the agar-water gel test. In the glass tube test, two cotton the agar-water gel test. In the glass tube test, two cotton plugs
plugs were were soaked soaked with with hydrochloric hydrochloric acid acid (HCl) (HCl) andand ammonium hydroxide (NH
ammonium hydroxide (NH44OH) and were inserted intoOH) and were inserted into both
both ends ends of of the the glass glass tube. tube. NHNH44OH. The substanceOH. The substance (NH
(NH44OH) with a lighter molecular weight of 35.0459 g/molOH) with a lighter molecular weight of 35.0459 g/mol diffused at a faster rate, resulting in the formation of a diffused at a faster rate, resulting in the formation of a white ring around the tube closer to the side of the white ring around the tube closer to the side of the substance with the larger molecular weight of 36.4611 substance with the larger molecular weight of 36.4611 g/mol (HCl). In the agar-water gel test, drops of potassium g/mol (HCl). In the agar-water gel test, drops of potassium permanganate,
permanganate, potassium potassium dichromate dichromate and and methylene methylene blueblue were simultaneously placed in separate wells in an agar were simultaneously placed in separate wells in an agar plate.
plate. Methylene Methylene blue, blue, with with the the largest largest molecular molecular weight,weight, had the smallest diameter (8.5 mm) and had the slowest had the smallest diameter (8.5 mm) and had the slowest diffusion rate (0.05 mm/min). Thus, the larger the diffusion rate (0.05 mm/min). Thus, the larger the molecular weight, the slower the rate of diffusion.
molecular weight, the slower the rate of diffusion.
INTRODUCTION INTRODUCTION
Diffusion is a process wherein molecules of gases collide and interact as a result Diffusion is a process wherein molecules of gases collide and interact as a result of random motion. This eventually leads to the uniform distribution of the molecules of of random motion. This eventually leads to the uniform distribution of the molecules of the involved gases throughout the system (Nave, 2008). Diffusion is a net movement of the involved gases throughout the system (Nave, 2008). Diffusion is a net movement of particles from an area of high concentration to low concentration (Traverso, 2004).
particles from an area of high concentration to low concentration (Traverso, 2004).
Several factors may affect the rate of diffusion of substances. These factors Several factors may affect the rate of diffusion of substances. These factors include the particle size or the molecular weight of the substance, the temperature in the include the particle size or the molecular weight of the substance, the temperature in the system, the concentration difference of the substances, the diffusion distance, the surface system, the concentration difference of the substances, the diffusion distance, the surface area, and the permeability of the barrier. The larger the particle, the greater the force area, and the permeability of the barrier. The larger the particle, the greater the force needed to move the particle. Thus, at a certain temperature, a smaller particle diffuses needed to move the particle. Thus, at a certain temperature, a smaller particle diffuses faster than a larger one (Meyertholen, n.d.).
The effect of molecular weight on the diffusion rate of gases can be observed with The effect of molecular weight on the diffusion rate of gases can be observed with the glass tube set-up. It involves simultaneously placing cotton plugs, separately the glass tube set-up. It involves simultaneously placing cotton plugs, separately moistened with two solutions, on opposite ends of a glass tube. The set-up is observed moistened with two solutions, on opposite ends of a glass tube. The set-up is observed until a white ring forms around the tube near the end of the substance with the larger until a white ring forms around the tube near the end of the substance with the larger molecular weight. In the experiment, hydrochloric acid (HCl) and ammonium hydroxide molecular weight. In the experiment, hydrochloric acid (HCl) and ammonium hydroxide (NH
(NH44OH) were used for easier comparison of the diffusion rates, since there is aOH) were used for easier comparison of the diffusion rates, since there is a significant difference in the molecular weights of the substances (HCl = 36.4611 g/mol; significant difference in the molecular weights of the substances (HCl = 36.4611 g/mol; NH
NH44OH = 35.0459 g/mol).OH = 35.0459 g/mol).
The agar-water gel set-up involves simultaneously placing drops of different The agar-water gel set-up involves simultaneously placing drops of different solutions in separate wells in an agar plate and measuring their diameters at regular time solutions in separate wells in an agar plate and measuring their diameters at regular time intervals. In the experiment, the solutions used were potassium permanganate (KMnO intervals. In the experiment, the solutions used were potassium permanganate (KMnO44),), potassium
potassium dichromate dichromate (K (K 22Cr Cr 22OO77) and methylene blue. The three substances possess) and methylene blue. The three substances possess distinct colors, making it easier to differentiate and measure their diameters.
distinct colors, making it easier to differentiate and measure their diameters.
This study aimed to determine the effect of molecular weight on the rate of This study aimed to determine the effect of molecular weight on the rate of diffusion of substances with respect to time via the agar-water gel test.
diffusion of substances with respect to time via the agar-water gel test. Specifically, it aimed to:
Specifically, it aimed to: 1.
1. identify the factors that affect the diffusion rate of substances; andidentify the factors that affect the diffusion rate of substances; and 2.
MATERIALS AND METHODS MATERIALS AND METHODS
In determining the effect of molecular weight on the diffusion rate of substances, In determining the effect of molecular weight on the diffusion rate of substances, the glass tube and agar-water gel set-ups were used. For the glass tube set-up, the the glass tube and agar-water gel set-ups were used. For the glass tube set-up, the materials used were a 30-cm glass tube, an iron stand with an iron ring, rubber bands, materials used were a 30-cm glass tube, an iron stand with an iron ring, rubber bands, cotton plugs, and NH
cotton plugs, and NH44OH and HCl solutions. For the agar-water gel set-up, the materialsOH and HCl solutions. For the agar-water gel set-up, the materials used were an agar plate with wells, potassium permanganate (KMnO
used were an agar plate with wells, potassium permanganate (KMnO44), potassium), potassium dichromate (K
dichromate (K 22Cr Cr 22OO77) and methylene blue. All the materials were acquired from the) and methylene blue. All the materials were acquired from the Dispensing Laboratory of the College of Science and Mathematics, University of the Dispensing Laboratory of the College of Science and Mathematics, University of the Philippines Mindanao Campus, Davao City.
Philippines Mindanao Campus, Davao City.
Glass Tube Set-up Glass Tube Set-up
The 30-cm glass tube was held level in place on the iron ring using the rubber The 30-cm glass tube was held level in place on the iron ring using the rubber bands. Two
bands. Two cotton cotton plugs plugs were separatelwere separately soaked y soaked in ammonium in ammonium hydroxide (NHhydroxide (NH44OH) andOH) and hydrochloric acid (HCl) and simultaneously inserted into both ends of the glass tube. hydrochloric acid (HCl) and simultaneously inserted into both ends of the glass tube. Four replicates were made. After some time, white rings of smoke formed on the inside Four replicates were made. After some time, white rings of smoke formed on the inside of the tubes. The positions were marked.
of the tubes. The positions were marked. The distances from the HCl and NH
The distances from the HCl and NH44OH plugs to the white rings were measuredOH plugs to the white rings were measured and recorded in centimeters (cm). The average distance from the substances to the and recorded in centimeters (cm). The average distance from the substances to the position
position of of the the white white smoke smoke was was calculated calculated by by summing summing up up the the total total distances distances andand dividing it by the number of replicates. A table comparing the measurements of the dividing it by the number of replicates. A table comparing the measurements of the distances was plotted and analyzed.
Agar-Water Gel set-up Agar-Water Gel set-up
A Petri dish containing agar-water gel with three wells was used as the medium A Petri dish containing agar-water gel with three wells was used as the medium for diffusion. Three solutions were used: potassium permanganate (KMnO
for diffusion. Three solutions were used: potassium permanganate (KMnO44), potassium), potassium dichromate (K
dichromate (K 22Cr Cr 22OO77) and methylene blue. These substances have different colors and) and methylene blue. These substances have different colors and molecular weights; KMnO
molecular weights; KMnO44has a purple color and has a molecular weight of 158 g/mol,has a purple color and has a molecular weight of 158 g/mol, K
K 22Cr Cr 22OO77 is a yellow solution and has a molecular weight of 294 g/mol, and methyleneis a yellow solution and has a molecular weight of 294 g/mol, and methylene blue is a blue solution with a molecular weight of 374
blue is a blue solution with a molecular weight of 374 g/mol. A drop of each solution wasg/mol. A drop of each solution was separately placed in the wells, and the Petri dish was immediately covered to avoid air separately placed in the wells, and the Petri dish was immediately covered to avoid air from affecting the diffusion rates of the solutions.
from affecting the diffusion rates of the solutions.
The diameters (in millimeters) of the colored areas were measured at three-minute The diameters (in millimeters) of the colored areas were measured at three-minute time intervals, beginning at t
time intervals, beginning at t00 = 0 minutes and ending at t= 0 minutes and ending at t1111= 30 minutes. The average= 30 minutes. The average rate of diffusion was calculated by taking the average of the computed partial values. The rate of diffusion was calculated by taking the average of the computed partial values. The partial diffusion rate was calculated using the following f
partial diffusion rate was calculated using the following formula:ormula:
Partial rate (r
Partial rate (rpp) = d) = dii – d– di-1i-1
ttii – t– ti-1i-1
where:
where:ddii = diameter of the colored area at a = diameter of the colored area at a given timegiven time
d
di-1i-1 = diameter of the colored area immediately be= diameter of the colored area immediately before dfore dii
ttii = time when d= time when dii was measuredwas measured
tti-1i-1 = time immediately before t= time immediately before tii
The computed values were tabulated, and the mean of the partial rates of each The computed values were tabulated, and the mean of the partial rates of each substance was calculated. The average diffusion rates of the substances were plotted substance was calculated. The average diffusion rates of the substances were plotted against their corresponding molecular weight. The partial rates of each substance were against their corresponding molecular weight. The partial rates of each substance were also plotted at time intervals. These tables and
RESULTS AND DISCUSSION RESULTS AND DISCUSSION
Table 1 shows the distances (in cm) of the smoke rings formed from the HCl- and Table 1 shows the distances (in cm) of the smoke rings formed from the HCl- and NH
NH44OH-soaked cotton plugs inserted into each end of the glass tube. The white smoke isOH-soaked cotton plugs inserted into each end of the glass tube. The white smoke is ammonium chloride (NH
ammonium chloride (NH44Cl), which is the product formed from the reaction of NHCl), which is the product formed from the reaction of NH44OHOH with HCl. It is observed that the distance from the smoke ring is generally closer to the with HCl. It is observed that the distance from the smoke ring is generally closer to the HCl end of the tube, ranging from 8 to 16.5 cm, compared to that with NH
HCl end of the tube, ranging from 8 to 16.5 cm, compared to that with NH44OH, whichOH, which ranges from 13 to 17.5 cm. The average distances of the smoke from NH
ranges from 13 to 17.5 cm. The average distances of the smoke from NH44OH and HClOH and HCl are 15.55 cm and 11.625 cm, respectively. This shows that the reaction occurred near the are 15.55 cm and 11.625 cm, respectively. This shows that the reaction occurred near the HCl end of the tube.
HCl end of the tube.
The size of the particle is inversely proportional to the rate of diffusion of the The size of the particle is inversely proportional to the rate of diffusion of the substance (Silberberg, 2000). Hydrochloric acid has a molecular weight of 36.4611 g/mol, substance (Silberberg, 2000). Hydrochloric acid has a molecular weight of 36.4611 g/mol, and Ammonium hydroxide has a molecular weight of 35.0459 g/mol. Since HCl has a and Ammonium hydroxide has a molecular weight of 35.0459 g/mol. Since HCl has a larger molecular weight, it diffuses slower than NH
larger molecular weight, it diffuses slower than NH44OH. Since NHOH. Since NH44OH diffused faster OH diffused faster than HCl, it was able to reach the HCl end of the glass tube faster than the HCl travelled than HCl, it was able to reach the HCl end of the glass tube faster than the HCl travelled towards the NH
towards the NH44OH end. The formation of the white smoke indicated that the NHOH end. The formation of the white smoke indicated that the NH44OHOH molecules have reached the HCl
molecules have reached the HCl molecules and were already reacting to molecules and were already reacting to form NHform NH44Cl.Cl.
It can be inferred from Table 1 that the rates of diffusion of substances are It can be inferred from Table 1 that the rates of diffusion of substances are inversely proportional to their corresponding molecular weights. The hypothesis, “if inversely proportional to their corresponding molecular weights. The hypothesis, “if molecular weight affects the diffusion rates of substances, then the higher the molecular molecular weight affects the diffusion rates of substances, then the higher the molecular weight of a substance, the slower the rate of
Table 1. Distance of the smoke
Table 1. Distance of the smoke ring from the HCl and NHring from the HCl and NH44OH ends of the glass tube.OH ends of the glass tube. Trial Trial Distance, d (cm) Distance, d (cm) Total distance, D Total distance, D Ratio Ratio d
dHClHCl dd NH4OH NH4OH ddHClHCl/D /D dd NH4OH NH4OH/D /D NH4OH/HClNH4OH/HCl 1 1 11 11 13 13 24 24 .4583 .4583 .5417 .5417 1.18181.1818 2 2 8 8 18 18 26 26 .3077 .3077 .6923 .6923 2.252.25 3 3 16.5 16.5 17.5 17.5 34 34 .4853 .4853 .5147 .5147 1.06061.0606 4 4 11 11 13.7 13.7 24.7 24.7 .4453 .4453 .5547 .5547 1.24551.2455
Table 2 shows the data for the agar-water gel set-up. The diameters of the areas Table 2 shows the data for the agar-water gel set-up. The diameters of the areas covered by the three substances (KMnO
covered by the three substances (KMnO44, , K K 22Cr Cr 22OO77 and methylene blue) were measuredand methylene blue) were measured (in mm) at three-minute intervals, starting at 0 minutes and ending at 30 minutes. The (in mm) at three-minute intervals, starting at 0 minutes and ending at 30 minutes. The average diameters were calculated, and KMnO
average diameters were calculated, and KMnO44 had the largest diameter (15.818 mm),had the largest diameter (15.818 mm), followed by K
followed by K 22Cr Cr 22OO77(14.455 mm), and methylene blue had the smallest diameter (7.909(14.455 mm), and methylene blue had the smallest diameter (7.909 mm). Potassium permanganate has a molecular weight of 158 g/mol, potassium mm). Potassium permanganate has a molecular weight of 158 g/mol, potassium dichromate is 294 g/mol, and methylene blue is 374 g/mol. With this, it can be observed dichromate is 294 g/mol, and methylene blue is 374 g/mol. With this, it can be observed that methylene blue, being the heaviest, had the smallest diameter covered. Meanwhile, that methylene blue, being the heaviest, had the smallest diameter covered. Meanwhile, potassium
potassium permanganate, permanganate, being being the the lightest, lightest, had had the the largest largest diameter diameter covered covered after after 3030 minutes. The diameters covered show the diffusion of the substances. These results minutes. The diameters covered show the diffusion of the substances. These results support the hypothesis that the higher the molecular weight, the slower the rate of support the hypothesis that the higher the molecular weight, the slower the rate of diffusion.
Table 2. Diameters of KMnO
Table 2. Diameters of KMnO44, , K K 22Cr Cr 22OO77 and methylene blue on the agar plate at three-and methylene blue on the agar plate at three-minute intervals. minute intervals. Time Time (minute) (minute) Diameter (mm) Diameter (mm) Potassium Potassium Permanganate, KMnO Permanganate, KMnO44 (158 g/mole) (158 g/mole) Potassium Dichromate, Potassium Dichromate, K K 22Cr Cr 22OO77 (294 g/mole) (294 g/mole) Methylene Blue Methylene Blue (374 g/mole) (374 g/mole) 0 0 8 8 8 8 77 3 3 10 10 10 10 77 6 6 12 12 12 12 77 9 9 13 13 12 12 77 12 12 16 16 15 15 88 15 15 17 17 15 15 8.58.5 18 18 18 18 16 16 8.58.5 21 21 18 18 17 17 8.58.5 24 24 20 20 18 18 8.58.5 27 27 21 21 18 18 8.58.5 30 30 21 21 18 18 8.58.5 Average Average 15.818 15.818 14.455 14.455 7.9097.909
Figure 1 shows the agar-water gel set-up after 30 minutes. It can be observed that Figure 1 shows the agar-water gel set-up after 30 minutes. It can be observed that the colored areas have different diameters. The darkest and largest colored area is the the colored areas have different diameters. The darkest and largest colored area is the potassium permanganate.
potassium permanganate. The The yellow-colored area yellow-colored area is potassium is potassium dichromate, and dichromate, and the bluethe blue and smallest one is methylene blue.
and smallest one is methylene blue.
Figure 1. The agar-water gel set-up after 30
Table 3. Partial and average rates of diffusion of KMnO
Table 3. Partial and average rates of diffusion of KMnO44, , K K 22Cr Cr 22OO77 and methylene blueand methylene blue on the agar plate at three-minute intervals.
on the agar plate at three-minute intervals. Time
Time (minute) (minute)
Partial rates of diffusion (mm/min) Partial rates of diffusion (mm/min) Potassium Permanganate Potassium Permanganate (158 g/mol) (158 g/mol) Potassium Dichromate Potassium Dichromate (256 g/mol) (256 g/mol) Methylene Blue Methylene Blue (375 g/mol) (375 g/mol) 3 3 0.6667 0.6667 0.6667 0.6667 00 6 6 0.6667 0.6667 0.6667 0.6667 00 9 9 0.3333 0.3333 0 0 00 12 12 1 1 1 1 0.33330.3333 15 15 0.333 0.333 0 0 0.16670.1667 18 18 0.333 0.333 0.3333 0.3333 00 21 21 0 0 0.3333 0.3333 00 24 24 0.6667 0.6667 0.3333 0.3333 00 27 27 0.3333 0.3333 0 0 00 30 30 0 0 0 0 00 Average Average 0.4333 0.4333 3.333 3.333 0.50.5
Table 3 shows the partial and average diffusion rates of the three substances. The Table 3 shows the partial and average diffusion rates of the three substances. The average diffusion rates show that potassium permanganate diffuses the fastest, followed average diffusion rates show that potassium permanganate diffuses the fastest, followed by
by potassium potassium dichromate, dichromate, and, and, lastly, lastly, methylene methylene blue. blue. Figure Figure 2 2 shows shows the the line line graph graph of of the partial diffusion rates in Table 3. Several times, the diffusion rate became zero at the partial diffusion rates in Table 3. Several times, the diffusion rate became zero at some intervals. According to Chang (1998), the rate of diffusion of a substance is some intervals. According to Chang (1998), the rate of diffusion of a substance is inversely proportional to the molecular weight. This is because the larger the particle, the inversely proportional to the molecular weight. This is because the larger the particle, the more energy is required to move the particle.
0 0 0.2 0.2 0.4 0.4 0.6 0.6 0.8 0.8 1 1 1.2 1.2 3 3 6 6 9 9 112 12 15 15 18 28 21 21 24 24 27 37 300 P P a a r r t t i i a a l l r r a a t t e e o o f f d d i i f f f f u u s s i i o o n n ( ( m m m m / / m m i i n n ) )
Time elapsed (min) Time elapsed (min)
Potassium Potassium Permanganate (158 Permanganate (158 g/mol) g/mol) Potassium Potassium Dichromate (256 Dichromate (256 g/mol) g/mol) Methylene Blue (375 Methylene Blue (375 g/mol) g/mol)
Figure 2. A line graph of
Figure 2. A line graph of the partial rates of diffusion of KMnO4,the partial rates of diffusion of KMnO4, K2Cr2O7 and methylene blue against the time elapsed. K2Cr2O7 and methylene blue against the time elapsed.
SUMMARY AND CONCLUSION SUMMARY AND CONCLUSION
The effect of molecular weight of the rate of diffusion was determined with the The effect of molecular weight of the rate of diffusion was determined with the agar-water gel set-up. Drops of potassium permanganate (KMnO
agar-water gel set-up. Drops of potassium permanganate (KMnO44), potassium), potassium dichromate (K
dichromate (K 22Cr Cr 22OO77) and methylene blue were simultaneously placed in separate wells) and methylene blue were simultaneously placed in separate wells in the agar plate. The di
in the agar plate. The diameters of the substances were measured at three-minute ameters of the substances were measured at three-minute intervals,intervals, from 0 minutes to 30 minutes.
from 0 minutes to 30 minutes.
The results showed that at the end of 30 minutes, KMnO
The results showed that at the end of 30 minutes, KMnO44had the largest diameter had the largest diameter covered at 21 mm, followed by K
covered at 21 mm, followed by K 22Cr Cr 22OO7,7,which covered 18 mm. Methylene blue had thewhich covered 18 mm. Methylene blue had the least covered area at 8.5 mm. The rates of diffusion of KMnO
least covered area at 8.5 mm. The rates of diffusion of KMnO4,4,K K 22Cr Cr 22OO77and methyleneand methylene blue are 0.43 mm/min, 0.33 mm/min, and 0.05 mm/min, respectively.
blue are 0.43 mm/min, 0.33 mm/min, and 0.05 mm/min, respectively.
The results acquired coincide with the hypothesis that if molecular weight affects The results acquired coincide with the hypothesis that if molecular weight affects diffusion rates, then the larger the molecular weight, the slower the diffusion rate of the diffusion rates, then the larger the molecular weight, the slower the diffusion rate of the substance. Aside from this, however, other factors such as temperature, concentration, the substance. Aside from this, however, other factors such as temperature, concentration, the diffusion medium used also affect the rate of diffusion.
LITERATURE CITED LITERATURE CITED
Chang, R. 1998. Chemistry 6
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http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/diffus.html Silberberg, M. S. 2000. Chemistry 2
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