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Getting started: particles and dissolving
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Everything is made of tiny particles. The particle model from KS3 explains states of matter, dissolving and diffusion, and you will use it all through GCSE Chemistry.
The particle model
Solid: particles close together in a regular pattern; they vibrate in fixed positions.
Liquid: particles close together but randomly arranged; they can move past each other.
Gas: particles far apart, moving quickly in all directions.
Heating gives particles more energy, so they move or vibrate more.
Liquid: particles close together but randomly arranged; they can move past each other.
Gas: particles far apart, moving quickly in all directions.
Heating gives particles more energy, so they move or vibrate more.
Dissolving
Solute: the substance that dissolves (for example salt).
Solvent: the liquid it dissolves in (for example water).
Solution: the mixture made.
Soluble substances dissolve; insoluble ones do not. A saturated solution cannot dissolve any more solute at that temperature.
The solute particles spread out between the solvent particles. They do not disappear, so mass of solution = mass of solute + mass of solvent.
Solvent: the liquid it dissolves in (for example water).
Solution: the mixture made.
Soluble substances dissolve; insoluble ones do not. A saturated solution cannot dissolve any more solute at that temperature.
The solute particles spread out between the solvent particles. They do not disappear, so mass of solution = mass of solute + mass of solvent.
Diffusion
Diffusion is the spreading out of particles from where there are many to where there are fewer, because they move randomly.
It is fast in gases, slower in liquids, and does not happen in solids.
It is faster at higher temperatures because the particles move faster.
It is fast in gases, slower in liquids, and does not happen in solids.
It is faster at higher temperatures because the particles move faster.
A student dissolves 20 g of sugar in 150 g of water. What is the mass of the solution?
- The sugar particles are still there, just spread out.
- Mass of solution = 20 + 150
Answer: 170 g
Solids vibrate in place, liquids slide past each other, gases move fast and far apart. Solute + solvent = solution, and mass is conserved when dissolving. Diffusion is fastest in gases and when hotter.
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