1.2. DIFFUSION
Definition:
Diffusion is the movement of molecules from one region of higher concentration to a region of lower concentration.
The difference in concentration of a substance between regions is called concentration gradient. When the concentration is high the rate of diffusion is greater.
Molecules of solid have little or no freedom of movement. Those of liquid are further apart and so they have some colliding with each other and so the molecules of gases have the highest form of liquid.
1.2.1. EXPIRIMENT TO DEMONSTRATE THE RATE OF DIFFUSION IN GASES
Requirements:
A glass tube with two corks at both end (one of the corks cotton wool which have been soaked in ammonia solution) Ammonia is an Alkali
Procedure:
little squares of red litmus paper are placed in the glass tube. They are placed in the glass tube at a regular distance stuck to the side of the tube. The cork containing ammonia solution is used to close the other end of the tube. Ammonia is alkaline and its vapor will diffuse along the tube. The rate of diffusion can be measured following the time is taken for each square piece of red litmus paper to turn blue
1.2.2. EXPERIMENT TO DEMONSTRATE THE RATE OF DIFFUSION IN LIQUIDS
Requirements:
test tube, gelatin, methylene blue, hot water.
Procedure:
some of the solution is put into a test tube up half full. A little of the gelatin is mixed with methylene blue(color) when the first layer of gelatin is set firmly we pour a narrow layer is also set firmly. We pour clearer gelatin over the blue layer when the blue color cools, it also set firmly and so we also pour clearer gelatin over the blue layer so that the blue layers sandwiched between the two clear layers
the experiment is allowed to stand for a week after which its noticed that the blue color or dye has diffused upward and downwards into the two clear layers to equal extend.
1.2.3. FACTORS AFFECTING DIFFUSION.
- CONCENTRATION: if the concentration is very high at the source, the rate of diffusion would be high and vice versa.
- TEMPERATURE. When the temperature increase, the rate of diffusion also increases. This is because the molecules move faster with increase in temperature.
- PRESSURE. Increase in pressure increases the rate of diffusion.
- SIZE OF THE MOLECULE. With large molecules the diffusion rate is slower than with lower viscosity
- NATURE OF SUBSTANCE. Gaseous substance diffuse faster than liquids and liquids substances faster than gaseous substances.
- VISCOSITY. substances with high viscosity diffuse less than substances in lower viscosity.
1.1.4. DIFFUSION IN LIVING ORGANISM.
Diffusion involves the uptake (taking in) and the expulsion (sending out) of substances in living organism e.g. the uptake of oxygen Is to the body and the expulsion.
In some cases, diffusion is too slow to meet up with the needs of organism and so it is taken over by the blood circulation and active transport.
click here for the next lesson: TURGIDITY AND FLACIDITY
