Effects of Concentration and Molecular Weight on Diffusion

A lab report from early 2016 when I was still a science newbie:

Introduction:  We attempted to discern what effect a solution’s molecular weight and concentration would have on its diffusion in an agar gel. 

Hypothesis:  Liquids with higher concentration will disperse faster than liquids of low concentration in the agar.  Liquids with high molecular weight will disperse slower than liquids of a low molecular weight at the same concentration. 

Equipment/reagents:   One Petri plate containing agar gel, a clean straw, Potassium Permanganate (KMnO4) at 3 concentrations (.1m, .01m, and .001m), Methylene Blue (C16H18ClN3S) at a concentration of .001m, and droppers for respective liquids.  Ruler. 

Method:  The clean straw is used to scoop out 4 holes evenly spaced in the agar gel.  The holes did not reach all the way down to the petri-dish.  1 drop of Potassium Permanganate was placed into each of 3 holes at each of the concentrations (.1m, .01m, and .001m).  One drop of Methylene Blue was placed in the remaining hole.  Petri dish was then covered and let sit undisturbed for 1 hour.  Afterwards Petri cover was removed and the diameter of the drops was measured in millimeters with the ruler. 

Data/results:  Potassium Permanganate (0.1m) spread to a diameter of 15mm.  Potassium Permanganate (0.01M) spread to a diameter of 10mm. Potassium Permanganate (0.001m) spread to a diameter of 4mm.  Methylene Blue (0.001m) spread to a diameter of 10mm.

Discussion:  Results showed that solutions of potassium permanganate with a higher concentration spread further than solutions with a lower concentration.  When comparing solutions of different molecular weight we found that the heavier Methlyene Blue spread further than Potassium Permanganate of equal concentration.       

Conclusion:  The results did not match our hypothesis.  From the results we can conclude that concentration and diffusion have a positive correlation in solutions of Potassium Permanganate.  Additionally we can conclude that Methlyene Blue has a higher rate of diffusion than Potassium Permanganate due to its heavier molecular weight.  Additional experiments would need to be done with other solutions to determine if there are other variables that would be effecting the rate of diffusion. 




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