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 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 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
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 |
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.