Rate of Diffusion of Potassium permanganate, Potassium dichromate, and Methylene blue1

Rate of Diffusion of Potassium permanganate, Potassium dichromate, and Methylene blue1 1 The Effect of Molecular Weight and Time on the Rate of Diffusion of Potassium permanganate, Potassium dichromate, and Methylene blue1 scientific paper submitted in partial fulfillment of the requirements in General Biology I laboratory under Prof. Diana Rose Gonzales, 1st sem., 2013 2014 _ 2 ABSTRACT The effect of molecular weight and time on the rate of diffusion of potassium permanganate, potassium dichromate, and methylene blue was tested using a petri dish of agar water gel with three wells. The three substances were dropped simultaneously in the petri dish. Potassium permanganate (MW 158g/mole) increased rapidly (14.50 mm) while Methylene blue (MW 374 g/mole) gradually increased (9.50 mm) only. Thus, molecular weight and time affects the rate of diffusion. INTRODUCTION Diffusion is a movement of molecules from an area of higher concentration to an area of lower concentration. The particles will fuse when they are evenly distributed and have reached equilibrium. Potassium permanganate, potassium dichromate, and methylene blue are substances used as indicators and oxidizing agents. Potassium permanganate is used in organic compounds and used commercially to purify water and sanitizer. It is chemically used to regulate certain reducing compounds. Potassium dichromate is used to determine ethanol concentrations in solutions and determine the presence and purity of silver. Researches also suggest that potassium dichromate functions as an agent that cause genetic mutation against DNA repair deficient strains of Escherichia coli. Lastly, methylene blue is used as dye to identify bacteria and nucleic acids. The dye will have the deepest shade of blue when in contact with acids. As indicators and oxidizing agents, the substances stated above must prove that their diffusion must be fast in order to do their functions. Due to their difference in molecular weight, a test was conducted to prove what substance is more recommendable _ 3 to be used in getting the rate of diffusion. To further verify the experiment rate of diffusion was also tested with time. To test this, agar water gel is one of the materials was used. Agar water gel is a substance that functions as a thickener, stabilizer, and emulsifier since it do not melt at room temperature until it is heated to 85oC and more. Also, with a stopwatch the substances were measured (mm) at a regular three minute interval for thirty minutes. The study aims to determine the effect of molecular weight and time on the rate diffusion of potassium permanganate, potassium dichromate, and methylene blue. The specific objectives are 1. to prove that molecular weight affects the rate of diffusion; and 2. to explain why molecular weight must also be observed with time MATERIALS AND METHODS In testing the effect of molecular weight and time on the rate of diffusion of potassium permanganate, potassium dichromate, and methylene blue, agar water gel was used. Three bottles with dropper containing the substances and a petri dish with agar water gel were given to each group. As three members of the group dropped all substances together in the wells of the agar water gel, the stopwatch started simultaneously with it. One member measured each wells of the agar water gel with a ruler to get the initial measurement (mm) of the wells. The group then drew the initial appearance of the experiment (Figure 4.1.). One member was assigned to signal the group if three minutes have passed and the member of the group who is assigned to _ 4 measure the wells will immediately but carefully measure the area with the ruler. There was a regular three minute interval for thirty minutes. After thirty minutes, the group then drew the final appearance of the experiment Figure 4.2. Also, the group computed for the average of the substances by adding all the data that were gathered divided by number of time intervals. To test the effect of time on the rate of diffusion the data gathered were computed by partial rate. Partial rate is computed by subtracting the diameter of colored area immediately (di-1) before the diameter of colored area at a given time (d1) divided by the time when d1 was measured (t1) minus the time immediately before t1 (ti 1). Again, the average of each substances were computed by adding all the date divided by the number of time intervals. A graph comparing the average rate of diffusion of each substance was plotted against its molecular weight in Figure 4.3. Also, a graph comparing the partial rate of diffusion of each substance was plotted against the time elapsed in Figure 4.4 _ 5 Potassium dichromate Methylene blue Potassium permanganate Figure 4.1. Initial appearance of the substances in the agar water gel wells. Potassium dichromate Methylene blue Potassium permanganate Figure 4.2. Final appearance of the substances in the agar water gel wells. _ 6 RESULTS AND DISCUSSIONS As seen in Table 4.2, potassium permanganate (MW 158 g/mole) has the highest average rate of diffusion with 11.32 mm/min, followed by potassium dichromate (MW 294 g/mole) with 10.86 mm/min, and methylene blue (MW 374 g/mole) with 7.95 mm/min. In Table 4.3, potassium permanganate has the highest partial rates of diffusion with 0.35 mm/min, followed by potassium dichromate with 0.32 mm/min, and methylene blue with 0.19 mm/min. This results shows that molecular weight has an effect in the rate of diffusion. When the molecular weight is lower then the rate of diffusion will be higher meaning they have an indirect relationship. Also, with time the rate of diffusion of the substances decreased, meaning time and the rate of diffusion has an indirect relationship. _ 7 SUMMARY AND CONCLUSION The effect of molecular weight and time on the rate of diffusion of potassium permanganate, potassium dichromate, and methylene blue was determined. Each substance was dropped simultaneously with each other into the petri dish with agar water gel. With a stopwatch the time was observed with an interval of three minuets in thirty minutes. After thirty minutes, the average of the circumference and the partial rates of diffusion were computed. Results showed that potassium permanganate (MW 158 g/mole) which has the least molecular weight had the highest average rate of diffusion compared to methylene blue (MW 374 g/mole), which has the greatest molecular weight among the three. In time, the circumference (mm/min) of each substance increased since there was diffusion in the agar water gel wells. Hence, molecular weight and time has an effect in the increase, decrease, slowness, and fastness of the diffusion of substances. Nevertheless, further experimentation must be done to improve the results of the experiment. It is recommended to use other substances, a different medium other than the agar water gel, a longer time period to test the diffusion, a more stable environment, and have more trials to observe better results. _ 11 LITERATURE CITED Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94. Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 137. Andrew Mills, David Hazafy, John A. Parkinson, Tell Tuttle and Michael G. Hutchings The Journal of Physical Chemistry A 2009, 113 (34), 9575-9576 Chongmok Lee, Yoo Wha Sung, and Joon Woo ParkThe Journal of Physical Chemistry B1999, 103 (5), 893-898 _