Diffusion is caused by kinetic energy , the energy of motion. Temperature is a measure of kinetic energy. Molecular movement due to kinetic energy is random. Molecular weight - Smaller molecules move faster than larger molecules. State of matter - Solid, liquid, gas.
Molecules move fastest in a gaseous environment and slowest in a solid environment.
You will be looking at all four properties during this investigation to determine the cause of diffusion. You will be required to predict the outcome of some experiments without actually performing them, but you should be able to accomplish this with little difficulty if you keep in mind the four properties listed above. This is rather like what would happen to a basketball if it were bombarded on all sides by ping pong balls. Water molecules are too small to see under the microscope, but you will observe the results of the water molecules hitting the baking soda particles - particle vibration. There will be many large particles which will not show Brownian movement.