Diffusion & Dilution (Edexcel IGCSE Chemistry)

Spec point — understand how the results of experiments involving the dilution of coloured solutions and diffusion of gases can be explained

Diffusion and dilution

• Diffusion and dilution experiments support a theory that all matter (solids, liquids and gases) is made up of tiny, moving particles

Diffusion

• Diffusion occurs in gases and liquids, due to the random motion of their particles

• It is where particles move from an area of high concentration to an area of low concentration

• Eventually the concentration of particles is even as the particles are evenly spread throughout the available space

• Diffusion happens on its own and no energy input is required

  • Although, it occurs faster at higher temperatures because the particles have more kinetic energy

Diffusion in gases

Diffusion of red-brown bromine gas

Description:

• Here, we see the diffusion of bromine gas from one gas jar to another
• After 5 minutes the bromine gas has diffused from the bottom jar to the top jar

Explanation:

• The air and bromine particles are moving randomly and there are large gaps between particles
• The particles can therefore easily mix together

Diffusion in liquids

Diffusion of potassium manganate(VII) in water over time

Description:

• When potassium manganate (VII) crystals are dissolved in water, a purple solution is formed
• A small number of crystals produce a highly intense colour

Explanation:

• The water and potassium manganate (VII) particles are moving randomly and the particles can slide over each other
• The particles can therefore easily mix together
• Diffusion in liquids is slower than in gases because the particles in a liquid are closely packed together and move more slowly

Dilution

• Dilution is the process of adding more solvent (usually water) to a solution

• This decreases the concentration of solute particles

• The solute particles become more spread out but are still present in the solution

• The colour of the solution becomes fainter with each dilution, but it does not disappear immediately

• Dilution does not remove particles

  • It spreads them out more

Dissolving potassium manganate (VII) in water

Description:

• When potassium magnate (VII) crystals are dissolved in water, the solution can be diluted several times
• The colour fades but does not disappear until a lot of dilutions have been done

Explanation:

• This indicates that there are a lot of particles in a small amount of potassium manganate (VII) and therefore the particles must be very small

Exam Hint Diffusion and dilution provide evidence for the kinetic theory of matter.