DIFFUSION THROUGH A CELL MEMBRANE
Diffusion is one of the very important processes by which substances such This activity will help you explore the relationship between diffusion and cell size by experimenting with model “cells.” Use this question to help formulate a hypothesis: What are the important factors that affect how materials diffuse into cells or. dependent on several factors, such as temperature, particle size, and the Formulate a hypothesis about the impact of molecular weight on the rate of diffusion of with a “P”. There should be a china or sharpie marker available for this. Get some Miskin tubing and put (say) starch into one and glucose into another and monitor the rates of diffusion into the surrounding water.
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In the glass tube test, two cotton plugs with equal sizes were soaked at the same rate to two different substances: The substance NH4OH having a lighter molecular weight diffused faster forming a white smoke.
For the agar-water gel set up, three solutions, namely, KMnO4, K2Cr2O7 and methylene blue, were dropped into three different wells in a petri dish of agar-water gel. Methylene blue displayed the smallest diameter and diffused at the slowest rate because it has the largest molecular weight. Hence, the higher the molecular weight, the slower the rate of diffusion. These molecules move in straight lines until they collide. The force moving these molecules is internal kinetic energy.
The collisions cause the molecules to distribute themselves equally in a given volume.
This process is called diffusion The Holt, Diffusion is the spreading of particles through random motion with the net movements from regions of higher concentration to regions of lower concentration wherein net diffusion can be restated as movement of particles along the concentration gradient.
According to Otto and Towle, there are external factors that influence the rate of diffusion of substances. In addition to molecular concentration, two other factors affect the rate at which diffusion occurs. One of this is temperature. The higher the temperature, the greater the speed of molecular movement. Hence, diffusion occurs from an area of higher temperature to one of lower temperature.
Similarly, pressure accelerates molecular movement, resulting in diffusion from a region of higher pressure to one of a lower pressure. Thus, the differences in molecular concentration, temperature and pressure affect diffusion referring to the force resulting from these differences as diffusion pressure.
Consequently, the study means that the rate of diffusion is inversely proportional to the size of the particle of the substance i. The validity that the molecular weight of a substance has an effect on its rate of diffusion was derivative from the glass tube set-up. At the same manner, the agar-water gel test is used to assess and verify the same matter. This study aimed to determine the effect of molecular weight and time on the rate of diffusion of substances via the glass tube test and agar-water gel test.
The specific objectives were 1. For the first set up, two feet glass tube was fastened horizontally to a ring strand, as shown in Figure 1.
Formulate a hypothesis about the relationship between molecule size and diffusion.?
Using fine forceps, two cotton balls of the same size were moistened, one with Figure 1. One end of the tube was then plug with one wet cotton ball and the other end with the other cotton ball. After some time, a white smoke appeared. The distance of the white smoke to each of the cotton balls was obtained by measuring its length, comparing each measurement and then getting the total distance and average ratio of the diffusion of the substances.
A graph comparing the distance of the substances with that of the white smoke was then plotted and analyzed. For the next set up, a petri dish of agar-water gel with three wells was obtained.
The three wells were labeled as follows: By definition, a system in equilibrium can undergo no net change unless some external action is performed on it e. Its behaviour is steady with time, and no changes appear to be occurring, even though the molecules are in ceaseless motion.
In contrast, the nonequilibrium properties describe how a system responds to some external action, such as the imposition of a temperature or pressure difference. Equilibrium behaviour is much easier to analyze, because any change that occurs on the molecular level must be compensated by some other change or changes on the molecular level in order for the system to remain in equilibrium. Equilibrium properties Ideal gas equation of state Among the most obvious properties of a dilute gas, other than its low density compared with liquids and solids, are its great elasticity or compressibility and its large volume expansion on heating.
These properties are nearly the same for all dilute gases, and virtually all such gases can be described quite accurately by the following universal equation of state: This expression is called the ideal, or perfect, gas equation of state, since all real gases show small deviations from it, although these deviations become less significant as the density is decreased. Here p is the pressure, v is the volume per moleor molar volume, R is the universal gas constantand T is the absolute thermodynamic temperature.
To a rough degree, the expression is accurate within a few percent if the volume is more than 10 times the critical volume; the accuracy improves as the volume increases. The expression eventually fails at both high and low temperatures, owing to ionization at high temperatures and to condensation to a liquid or solid at low temperatures.
Design an experiment to test how the realtionship between molecule size and rate of diffusion?
The ideal gas equation of state is an amalgamation of three ideal gas laws that were formulated independently.
Touching the Spring of the Air. The law states that the volume of a gas at constant pressure is directly proportional to the absolute temperature; i.
The third law embodied in equation 15 is based on the hypothesis of the Italian scientist Amedeo Avogadro —namely, that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
Thus, at constant temperature and pressure the volume of a gas is proportional to the number of moles. By measuring the quantity of gas in moles rather than grams, the constant R is made universal; if mass were measured in grams and hence v in volume per gramthen R would have a different value for each gas. The ideal gas law is easily extended to mixtures by letting n represent the total number of moles of all species present in volume V. That is, if there are n1 moles of species 1, n2 moles of species 2, etc.
A brief aside on units and temperature scales is in order. The Kelvin thermodynamic temperature scale is defined through the laws of thermodynamics so as to be absolute or universal, in the sense that its definition does not depend on the specific properties of any particular kind of matter.
Its numerical values, however, are assigned by defining the triple point of water—i. The freezing point of water under one atmosphere of air then turns out to be by measurement The precise thermodynamic definition of the Kelvin scale and the rather peculiar number chosen to define its numerical values i. The gas constant R is determined by measurement. The best value so far obtained is that of the U.
National Institute of Standards and Technology—namely, 8. Internal energy Once the equation of state is known for an ideal gas, only its internal energy, E, needs to be determined in order for all other equilibrium properties to be deducible from the laws of thermodynamics.
That is to say, if the equation of state and the internal energy of a fluid are known, then all the other thermodynamic properties e. Proofs of such statements are usually rather subtle and involved and constitute a large part of the subject of thermodynamics, but conclusions based on thermodynamic principles are among the most reliable results of science.
A thermodynamic result of relevance here is that the ideal gas equation of state requires that the internal energy depend on temperature alone, not on pressure or density.
Effect of Molecule Size on Diffusion Rate by Emily Wo on Prezi
The actual relationship between E and T must be measured or calculated from known molecular properties by means of statistical mechanics. The internal energy is not directly measurable, but its behaviour can be determined from measurements of the molar heat capacity i. A system with many kinds of motion on a molecular scale absorbs more energy than one with only a few kinds of motion.
The interpretation of the temperature dependence of E is particularly simple for dilute gases, as is shown in the discussion of the kinetic theory of gases below. The following highlights only the major aspects.
For monatomic gases, such as helium, neonargonkryptonand xenonthis is the sole energy contribution. Gases that contain two or more atoms per molecule also contribute additional terms because of their internal motions: Some of these internal motions may not contribute at ordinary temperatures because of special conditions imposed by quantum mechanicshowever, so that the temperature dependence of Eint can be rather complex.
The extension to gas mixtures is straightforward—the total internal energy E per mole is the weighted sum of the internal energies of each of the species: It is the task of the kinetic theory of gases to account for these results concerning the equation of state and the internal energy of dilute gases.
Transport properties The following is a summary of the three main transport properties: These properties correspond to the transfer of momentumenergy, and matter, respectively.
Viscosity All ordinary fluids exhibit viscosity, which is a type of internal friction. A continuous application of force is needed to keep a fluid flowing, just as a continuous force is needed to keep a solid body moving in the presence of friction.
Consider the case of a fluid slowly flowing through a long capillary tube. It also depends on the geometry of the tube, but this effect will not be considered here. To a rough approximation, liquids are about times more viscous than gases. There are three important properties of the viscosity of dilute gases that seem to defy common sense.
All can be explained, however, by the kinetic theory see below Kinetic theory of gases. The first property is the lack of a dependence on pressure or density. Intuition suggests that gas viscosity should increase with increasing density, inasmuch as liquids are much more viscous than gases, but gas viscosity is actually independent of density. This result can be illustrated by a pendulum swinging on a solid support.
It eventually slows down owing to the viscous friction of the air. If a bell jar is placed over the pendulum and half the air is pumped out, the air remaining in the jar damps the pendulum just as fast as a full jar of air would have done.
Robert Boyle noted this peculiar phenomenon inbut his results were largely either ignored or forgotten. The Scottish chemist Thomas Graham studied the flow of gases through long capillaries, which he called transpiration, in andbut it was not until that the German physicist O.
When James Clerk Maxwell discovered in that his kinetic theory suggested this result, he found it difficult to believe and attempted to check it experimentally. He designed an oscillating disk apparatus which is still much copied to verify the prediction. The second unusual property of viscosity is its relationship with temperature. This behaviour was clearly established in by Graham.
The third property pertains to the viscosity of mixtures.Lab Protocol - Dialysis Tubing Experiments (Unit 7 Diffusion)
A viscous syrup, for example, can be made less so by the addition of a liquid with a lower viscosity, such as water. By analogyone would expect that a mixture of carbon dioxide, which is fairly viscous, with a gas like hydrogenwhich is much less viscous, would have a viscosity intermediate to that of carbon dioxide and hydrogen.
Surprisingly, the viscosity of the mixture is even greater than that of carbon dioxide. This phenomenon was also observed by Graham in Finally, there is no obvious correlation of gas viscosity with molecular weight.
Heavy gases are often more viscous than light gases, but there are many exceptions, and no simple pattern is apparent. Heat conduction If a temperature difference is maintained across a fluid, a flow of energy through the fluid will result.