Question

nvestigation of Factors Affecting the Rate of Diffusion

In addition to the concentration gradient (i.e. the difference in the concentration of particles between two environments) there are many other factors known to affect the rate of diffusion including;

temperature

the size of the diffusing particles

the viscosity of the medium through which the particles move

The purpose of this exercise is for you to work in groups to design experiments to test two of the factors listed above. You will be provided with access to the materials described below including;

0.5% malachite green (mw 927.1)

       1% potassium permanganate (mw 158.04)

       0.5% potassium permanganate

       1% agar plates (maximum of 2 per group)

2% agar plates (maximum of 2 per group)

plastic straws that could create uniform wells in the agar

discs of paper and forceps

pipettes (to dispense small volumes of solutions)

crushed ice and zip lock baggies

State your hypotheses and describe your experimental designs in the spaces below and then discuss these with your instructor/TA before continuing. Be sure you have considered appropriate controls, the number of replicates you intend to run and what data you are going to collect.

Hypothesis #1 (1 mark)

Experimental Design #1 (1 mark)

       

Hypothesis #2 (1 mark)

Experimental Design #2 (1 mark)

Answer 1

Hypothesis #1- Due to increase in molecular weight/size of the particle rate of diffusion decreases.

Hence here we should test that, Malachite green due to its higher molecular weight will diffuse slowly as compared to pottasium permanganate of same concentration.

Experimental design#1:

1.Take one 2% agar plate

2. Dig two uniform holes in it by using straw.

3. Fill one well with 0.5% malachite green and the other well with 0.5% pottasium permanganate

4. Let the solutions to diffuse through agar medium and note the zone of diffusion for both after regular time intervals i.e 10 min, 20min, 30 min respectively.

(Note: make sure that the two solutions should be of equal percentage because if concentration gradient is different for the two test solutions i.e 1% pottasium permanganate and 0.5% malachite green then may be the results obtained is due to concentration difference and not because size of the particle. Remember diffusion is the movement of molecules from higher to lower concentration hence the concentration of the two solutions must be strictly similar)

Hypothesis #2 The rate of diffusion slows down when the viscosity of the medium through which the particles move increases.

Hence the hypothesis to be tested here is that, all the three solutions when placed on different percentage of agar, difusses differently, i.e on 1% agar solution rate of diffusion is faster as compared to 2% agar solution for all the three test solutions because 1% agar is less viscous than 2% agar.

Experimental design #2:

1. Take one agar plate of 1% and 2% each.

2. Dip two paper disc in 0.5% pottasium permangante, two in 1% pottasium permanganate and two in 0.5% malachite green.

3. Put each of these discs on 1% and 2% agar plates at equal distance.

4. Note and compare the zone of diffusion on both the agar plates for all the three solutions after equal interval of time i.e 10 min, 20min and 30 min respectively.