The diffusion coefficient 10 th task

…the main task  Using a microscope, observe the Brownian motion of a particle of the order of micrometre in size.  Investigate how the coefficient of diffusion depends on the size and shape of the particle.

…what we were supposed to do?  We were supposed to observate various particles - in our case permanganate, pollen, hair pieces and fishing lines (pictures in next slide).  According to the observation we should find out how the diffusion coefficient depends on the size and shape of the particle.

permanganate fishing lines pollen hair pieces

To the top… …what´s the Brownian motion?  Brownian motion is an random motion microscopic particles in liquid or gaseous medium.  The explanation of Brownian motion is that molecules in solution constantly collide with the fact that the directions and a forces of these collisions are random.

The theory …  1. Our measurement is based on Einstein-Smouluchowsi equation which says us that diffusion coefficien „D“ is:  directly proportional to the square of central shift  inversely proportional to the double time of observation  2. To get the central shift we have to observate the particle for several times in small time intervals and square individual measured shifts in one direction.  3. The sum of individual squared shifts must be divided by count of measurements and the result must be square rooted.

…the central shift

…the experiment  We firstly poured pigment to a small amount of water in Petri dish. Than we made an observation to measure the intensity of the Brownian move.  This process we repeated ten times and with three other particles.

…the main measurement permanganatepollenhair piecefishing line Measurement 1 0,90,50,30,6 2 0,7 0,20,3 3 0,70,60,30,49 4 1,10,40,5 5 0,90,70,41 6 0,60,40,30,84 7 0,950,50,4 8 0,80,40,2 9 10,80,3 10 0,650,50,21 PermanganatePollenfishing line hair piece 0, , , ,

…the conclusion  According to the experiment we found out that diffusion coefficient depends on size and shape of particles.  The highest coefficient had the spherical and the smallest particle of permanagate.  On the contrary the lowest coefficient had irregular and large particle of hair.