Movement of Particles

This lesson covers:

  1. What diffusion is 
  2. The diffusion of bromine gas in air 
  3. The diffusion of potassium manganate(VII) in water
  4. The diffusion and reaction of ammonia and hydrogen chloride

Diffusion

Diagram showing diffusion with particles moving from higher concentration to lower concentration.

Diffusion is the movement of particles from areas of higher concentration to areas of lower concentration. 

This happens because particles move about randomly, so over time will spread out, moving from where there are lots of them (higher concentration), to where there are fewer of them (lower concentration).

stronger / weaker / higher / lower / same


Diffusion is the movement of particles from areas of concentration to areas of concentration. 

higher
lower

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Diffusion of bromine gas in air

Image showing bromine gas in a flask, illustrating the diffusion of bromine gas in air.

Bromine gas is brown, so we can easily see it spreading out by looking at where the brown colour spreads.

Diagram showing the diffusion of bromine gas in air. Initially separated by a glass plate, bromine gas spreads from the bottom tube to the top tube over time until evenly distributed.

This diagram shows two test tubes that are initially separated by a glass plate. Once the glass plate is removed, the bromine gas diffuses from the bottom tube to the top tube, until in the end it is evenly distributed

Diffusion of potassium manganate (VII) in water

Diagram showing the diffusion of potassium manganate VII in water over time.

Potassium manganate(VII) is a bright purple colour. If you place a lump of it in water it will initially sink to the bottom. As some of the potassium manganate(VII) particles start to diffuse throughout the beaker of water, the colour will slowly spread out.


Eventually, the particles will have diffused evenly throughout the beaker and it will all be the same colour

Diffusion and reaction of ammonia and hydrogen chloride:

Diagram showing diffusion and reaction of ammonia and hydrogen chloride in a glass tube forming a ring of ammonium chloride.
  1. This experiment uses one piece of cotton wool soaked in aqueous hydrogen chloride (HCl), and another piece soaked in aqueous ammonia (NH3). These pieces are placed at either end of a sealed glass tube.
  2. As the NH3 and HCl evaporate into gas, they begin to diffuse along the glass tube towards each other.
  3. When these gases meet, they'll react together to form ammonium chloride (NH4Cl), which will be visible as a white ring around the tube.
  4. Importantly, the white ring will be closer to the end with the HCl cotton wool. This is because NH3 particles are smaller than HCl particles and so diffuse more quickly. This means the NH3 particles will travel further before the NH3 and HCl react. 

What colour is bromine gas?

Brown

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What colour is potassium manganate(VII)?

Purple

Red

Yellow

Brown

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Are particles of ammonia or particles of hydrogen chloride larger?

Ammonia

Hydrogen chloride

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Illustration showing hydrogen chloride gas and ammonia gas reacting to form a solid compound.

Hydrogen chloride gas and ammonia gas react together to form a solid compound.

What is the name of this compound? 

Ammonium chloride

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Diagram showing the formation of ammonium chloride closer to cotton wool soaked in hydrochloric acid compared to cotton wool soaked in ammonia.

In the diagram, will the ring of ammonium chloride form closer to the cotton wool soaked in ammonia or the cotton wool soaked in hydrochloric acid?

Cotton wool soaked in ammonia

Cotton wool soaked in hydrochloric acid

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