Diffusion in gases
4 marks · NormalFigure 1 shows an apparatus used to investigate the diffusion of bromine gas.
State what you would observe if the lid between the two gas jars is removed.
Explain why the observation described in (a) happens, using ideas about particles.
Suggest why the bromine gas eventually spreads throughout both jars.
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(a) The brown colour of bromine gas spreads up into the jar containing air until both jars are evenly brown.
(b) Bromine particles and air particles move around randomly. Bromine particles spread out and mix with air particles by diffusion, from a region of high concentration (jar B) to low concentration (jar A).
(c) Particles move to fill all available space, so eventually the concentration of bromine is the same throughout both jars.
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Marking points
B1 (a) · 1 mark · Correct observation: brown colour spreads through both jars or jars become evenly brown.
M1 (b) · 1 mark · States that particles move at random or describes movement of particles.
M2 (b) · 1 mark · Relates to diffusion: particles spread from high to low concentration / mix by diffusion.
B2 (c) · 1 mark · States that particles spread out to fill available space/concentration becomes even.
Worked solution
(a) The brown colour of bromine gas slowly spreads up from jar B into jar A until both jars are an even brown colour.
(b) Bromine particles move randomly and mix with air particles. The particles spread out by diffusion, from a region of high concentration to a region of low concentration, causing the colour to spread.
(c) The process continues until the particles are evenly mixed and the concentration is the same throughout both jars.