Experiment to demonstrate how the rate of diffusion is affected by distance
We set up a glass tube horizontally with a clamp and stand, and placed red litmus paper at 5cm intervals for 50cm. we then soaked some cotton wool in ammonium hydroxide solution, and placed it at one end of the glass tube. We put rubber bungs in both ends, and started a stopwatch to time how long it took each piece of litmus paper to turn entirely blue from the ammonia gas.
To ensure the experiment was reliable, we waited until the piece of litmus paper turned entirely blue before writing down the time. Also, we accurately measured the distance between each piece of litmus paper using a metre ruler.
Distance offirst end of litmus paper from cotton wool Time taken for litmus paper to turn entirely blue(in seconds)
5cm 10cm15cm20cm25cm30cm35cm40cm45cm 204590140210290395538704
The graph has a clear upward sloping curve showing the correlation between the distance of the litmus paper from the cotton soaked in ammonium hydroxide and the amount of time taken for the litmus paper to turn blue.
This is because as the particles of ammonium hydroxide collide with each other and become forced further out during their diffusion through the air in the tube. However, the particles that move further are less concentrated and not as close together, so there is less collisions between the molecules, so they don't move out as quickly. This represents itself as the curve in the graph.
Diffuses from high concentration to low concentration because of concentration gradient.
NH4 and OH ions diffuse. Collide with air particles.
Diffusion due to random kinetic movement.