Specification Point 1.3: 
Understand how the results of experiments involving the dilution of coloured solutions and diffusion of gases can be explained

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

Diffusion 1: Bromine Gas

Diffusion of bromine gas

Diffusion of red-brown bromine gas

Description:

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

Explanation: 

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

Diffusion 2: Potassium Manganate Solution (VII)

Diffusion of Potassium Manganate, IGCSE Chemistry revision notes

Diffusion of potassium manganate 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 of Coloured Solutions

Potassium manganate dissolving in water

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 magnate (VII) and therefore the particles must be very small.
Specification Point 1.4: 
Know what is meant by the terms: • solvent • solute • solution • saturated solution

Terminology

Term Meaning Example
Solvent The liquid in which a solute dissolves The water in seawater
Solute The substance which dissolves in a liquid to form a solution The salt in seawater
Solution The mixture formed when a solute is dissolved in a solvent Seawater
Saturated solution A solution with the maximum concentration of solute dissolved in the solvent Seawater in the Dead Sea
Soluble Describes a substance that will dissolve Salt is soluble in water
Insoluble Describes a substance that won’t dissolve Sand is insoluble in water

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.