# Relationship between molecular weight and rate of diffusion

### How does molecular weight affect the rate of diffusion? | Socratic The rate of diffusion (Urms) is given by: Urms=√3RTMM. Where MM is the molar mass of the gas. Thus, when MM increases, the diffusion rate. Molecular weight is indirectly proportional to the rate of diffusion: the smaller, lighter The rate of diffusion has a direct relationship with the concentration gradient, the difference between the two concentrations, the faster the rate of diffusion. Jarrel Dean A. Yecyec ABSTRACT The effect of molecular weight in the rate of diffusion was determined by placing potassium permanganat.

These molecules move in straight lines until they collide.

• How does molecular weight affect the rate of diffusion?
• Graham's law
• What is the relationship between molecular weight and rate of diffusion?

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.

## Relationship between molecular weight and rate of diffusion?

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.

Graham's law of diffusion - Respiratory system physiology - NCLEX-RN - Khan Academy

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. Using fine forceps, two cotton balls of the same size were moistened, one with Figure 1.

### Graham's law - Wikipedia

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: Each well was placed with one drop of the prepared solution of each substance. The petri dish was then immediately covered and the diameter in mm.

At a regular five-minute interval for thirty minutes, the diameter of the colored area of each substance was measured and recorded, as shown in Figure 3. A graph comparing the distance of each interval to its original position was also plotted and analyzed. The position of the substances at zero minute. When passing by a bakery shop, we can directly smell the aroma of the bread and when going to a perfume store, we can soon smell the fragrance of the perfume.

Diffusion is one of the properties observed in the study of gases, and it is generally a characteristic of all gases Metcalfe, It is referred as the random, thermal motion of the particles and the net diffusion is the movement of particles from a higher area of concentration to the lower area of concentration Meyertholen, It may be affected by various factors including the size of the particles or the molecular weight of a substance, temperature, concentration difference, diffusion distance, surface area, and permeability.

Particles do not always have the same size or molecular weight. This results to their difference in some characteristics such as the rate of diffusion. At a given temperature, a substance having lower molecular weight tends to move faster than a substance having higher molecular weight. Thus, a substance with the lower molecular weight possesses a higher rate of diffusion.

Silberberg states that given two gases at equal pressure, e. NH3 and HCl, moving through another gas, e. Two cotton plugs moistened with hydrochloric acid HCl and ammonium hydroxide NH4OH were simultaneously plugged in the tube.

A white ring of smoke formed inside the glass tube nearer to the HCl. NH4OH diffused in a faster rate with an average distance of Hence, we can infer that the higher the molecular weight of a substance, the lower its rate of diffusion see Results and Discussion. Another experimental setup can be used to test this inference.

Based from the hypothesis inferred, the agar-water gel setup was conducted. A drop of potassium permanganate KMnO4potassium dichromate K2Cr2O7 and methylene blue was 2 placed to three separate wells in the agar-water gel on a petri dish. The setup lasted to 25 minutes. The three stains stated possess colors different from each other that they can be easily distinguished and measure their diameters within the given time with a regular interval of five minutes. In this regard, the study aimed to determine the effect of molecular weight on the rate of diffusion of substances. The specific objectives were: The tube test was initiated with the preparation of the set-up which was a two-feet glass tube placed horizontally to a pair of stand and locked with a clip.

Two cotton balls of the same size were dipped slightly, thoroughly and simultaneously to a hydrochloric acid HCl and the other to an ammonium hydroxide NH 4OH. Immediately, the two cotton balls were plugged simultaneously to both ends of the glass tube as shown in Figure 1.

The point where the cotton balls were plugged was then marked. Glass Tube Set-up School Science Lessons, After a white ring of smoke appeared inside the glass tube, the point where it was seen was marked. The distance from each initiation point of the cotton balls to the point where the smoke appeared was measured using a ruler.

The same procedure was done by the 4 groups and data were gathered. The total distance was calculated by adding the distances of the two substances from each initial point.

The ratio of the distance of each substance to the total distance was also computed as well as the ratio of one substance to the other and its average. Agar-water gel setup One drop of potassium permanganate KMnO4potassium dichromate K2Cr2O7 and methylene blue was simultaneously placed to each of the three wells in the agar-water gel.

Immediately, the petri dish was covered and the diameter of each colored area of the well was measured using a ruler, excluding the stains around it. The measured diameter was recorded for zero minute. After five minutes, the diameter of each well was again measured and recorded for five minutes.

The same recording was done with a regular interval of five minutes until reaching 25 minutes. The relationship of molecular weight of substances to its average rate of diffusion and relationship of time to the partial rates of diffusion of substances were presented through a graph as shown in Figures 3 and 4.

The white ring of smoke, as said on the introduction of the study, is the result of the reaction between the NH4OH and HCl. That is, the point where the molecules of the two substances met and formed a solid product.