The core purpose of the first experiment conducted in the lab was to study the principle of diffusion. The experiment aimed at analyzing the movement of molecules from a region of higher concentration towards lower concentration. Potassium permanganate crystals were dissolved in water to observe the process of diffusion. The observations and results attained from the experiment indicated the movement of molecules which occurred due to molecular collisions, taking place more frequently in areas of higher concentration.
Molecules present in a liquid or a gas move about constantly in random directions. During their movement, they bump into each other and bounce this way and that way. This random movement ultimately results in the uniform or even distribution of molecules. The tendency of molecules to spread out evenly throughout the space occupied by them is referred as diffusion. The process of diffusion does not require any sort of cellular energy; in fact the molecules diffuse due to their own natural movement which is called Brownian Motion. Since diffusion only needs kinetic energy from the environment, it is referred as passive transport (Lauren et al., 2010).
The movement of molecules always takes place form higher concentration region towards lower concentration region. The difference in the concentration between the two regions before diffusion occurs is called the concentration gradient. When a substance is higher in concentration on one side of the membrane, the molecules of the substance possess a tendency of moving across the membrane down its concentration gradient. Figure 1 illustrates the principle of diffusion, where molecules start moving gradually from high concentration area towards low concentration area.
Figure 1: Diffusion of molecules from higher concentration area to low concentration area.
The experiment conducted aimed at observing the process of diffusion and the movement of molecules taking place from a region of higher concentration towards lower concentration. The experiment observed the diffusion of potassium permanganate crystals in water. Our hypothesis was that permanganate crystals will diffuse in water and change the color of water. The observations attained from the experiment indicated the transfer of kinetic energy among molecules of the solute and solvent and how the molecules spread evenly all over water. The beaker in which potassium permanganate was dissolved was observed for several minutes without disturbance, in order to observe the random motion of molecules and their diffusion in water.
Potassium permanganate crystals are dark purple in color. When they were placed in water, the purple color of permanganate started to spread gradually in water. The water was observed constantly without any disturbance in order to identify the gradual process of diffusion of permanganate crystals into water. After some time, the entire crystals got spread evenly throughout water making it purple colored with the same shade. Figure 2(a) indicates the initial stage when potassium permanganate crystals were placed in water, and they can be seen concentrated at one side of the beaker in dark purple color. Figure 2(b) represents the stage where potassium permanganate crystals diffused into water imparting a light purple color to water, while some concentrated crystals can be seen at the bottom of the beaker. This is the stage where molecules had moved down their concentration gradient. Figure 2(c) indicates the stage where molecules of permanganate had evenly spread across the entire water in the beaker and there was no concentration gradient then.
2(a) 2(b) 2(c)
Figure 2(a): High concentration gradient existing between KMnO4 crystals and water.
Figure 2(b): Movement of molecules of KMnO4 into water (Diffusion)
Figure 2(c): Equilibrium reached. No concentration gradient exists now.
In the experiment conducted, the crystals of potassium permanganate have molecules which were tightly packed together, that is the molecules were quite concentrated. The water surrounding the permanganate crystals does not contain any concentration of permanganate molecules. Thus the permanganate molecules present in the crystals move into water until they distribute themselves evenly throughout water (Mitchelmore & Robert, 1985).
Each molecule of permanganate transfers its Kinetic energy to other molecules which cause a shift in the velocities of both molecules. The net result is each molecule seems to be moving in a random fashion. The whole group of large molecules that start out concentrated in a small area moves from the region of high concentration to a region of low concentration. Thus in short, a net movement of permanganate molecules occur which takes them away from the crystal into the water. This shows that the process of diffusion has taken place, indicating that the presence of concentration gradient resulted in the flow of molecules from a region of higher concentration towards lower concentration.
The experiment was conducted to observe the principle of diffusion and the net movement of molecules taking place from high concentration region towards low concentration region. Potassium permanganate crystals were dissolved in water to observe diffusion. The dark purple colored permanganate crystals turned entire water into a light purple colored solution, indicating the even distribution of molecules throughout. This proved our hypothesis, which also stated that permanganate will diffuse in water and will change its color. The experiment showed that diffusion will occur if the concentration gradient differs between two regions and molecules will move down from a region where they are highly concentrated towards a region where their concentration is less.
The experiment conducted aimed at analyzing the process of osmosis and the effect of varying solution concentrations on osmosis. The experiment analyses the mass of decalcified eggs before and after placing them in glucose solutions of varying concentrations and water. The experiment aimed at providing an understanding of isotonic, hypertonic and hypotonic solutions and their effect on the process of osmosis. The experiment placed four eggs in water, 0.5M, 1M and 2M glucose solution and the size of eggs was observed in each beaker. The results indicated that the eggs underwent changes in their weight due to osmosis presenting the fact that the concentration of solute in solutions affects osmosis.
Osmosis is referred as a special case of diffusion, and is defined as the net movement of water through a semi-permeable membrane (Mitchelmore & Roberts, 1985). This implies that osmosis involves flow of water or any fluid from an area of higher concentration towards an area of low concentration.
Osmosis depends greatly upon the concentration of solute present in a solution (Science Encyclopedia, 2011). Hypertonic solutions refer to a solution having higher concentration of solute than the solvent. Hypotonic solutions are the ones having lower concentration of solute in comparison to the solvent, while isotonic solutions have equal solute and solvent concentration.
The experiment conducted in the lab had the objective of studying the impact of concentration of solution on osmosis. This was done by observing the size of decalcified eggs after placing them in four different solutions having different concentrations of sugar and water in them. The experiment was done with water, 0.5M, 1.5M, and 2.0M glucose solutions. Our hypothesis that the size of the egg will remain the same in water, it will increase in 0.5M solution, decrease in 1.5M solution and 2.0M solutions. It was observed that the size of the egg placed in the four beakers varied in accordance with the concentration of sugar present in the solution.
The size of the decalcified was observed at regular interval of 15 minutes for 90 minutes in all the four beakers, and the observations obtained in the mass of the egg are listed in Table 1. Table 2 indicates the percentage change occurring in the mass of the eggs at regular intervals of 15 minutes. The percentage change is calculated using the following formula:
% change in mass = new mass -- initial mass x 100
Table 1: The masses (grams) of decalci-ed eggs in solutions of 0.5M, 1.5M and 2M glucose and Water measured at 15 minute intervals.
Initial Mass (g) (Time 0)
% change 15 min
% change 30 min
% change 45 min
% change 60 min
% change 75 min
% change 90 min
0.5 M. glucose
1.5 M. glucose
2.0 M. glucose
Table 2: Percent (%) change ( + or -) in the mass of eggs soaked in various solutions over time.
A graph was also plotted between the % change in mass of egg and the time intervals. The graph obtained from the observations mentioned above is as follows:
Time of Diffusion
% Change in Mass of Eggs
Time of Diffusion
Figure 3: Graph between % Change in mass of Eggs and Time of Diffusion