Simple Diffusion ExperimentsOxford AQA IGCSE Chemistry: Flashcards

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What is diffusion?

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What is diffusion?: The net movement of particles from an area of higher concentration to an area of lower concentration, due to random particle motion.
What does diffusion provide evidence for?: The existence of particles and their constant, random movement.
What gas is used to demonstrate diffusion in air, showing an orange-brown colour spreading?: Bromine (Br₂).
What two substances are used in the ammonia/hydrochloric acid diffusion tube experiment?: Ammonia solution (NH₃) and concentrated hydrochloric acid (HCl), on cotton wool at opposite ends of a tube.
What forms where ammonia and hydrogen chloride gases meet in the tube?: A white ring/smoke of ammonium chloride.
Why does the white ring form closer to the hydrochloric acid end?: Because ammonia molecules are lighter and diffuse faster than the heavier hydrogen chloride molecules.
What substance is used to demonstrate diffusion in a liquid?: Potassium manganate(VII) (KMnO₄), a purple crystal placed in water.
What is observed when potassium manganate(VII) is placed in water?: Its purple colour spreads outward through the water over time without stirring.
Is diffusion faster in gases or liquids?: Gases — because gas particles move faster and are further apart.
Why is diffusion slower in liquids than in gases?: Because liquid particles are closer together and move more slowly.
What colour is bromine gas?: Orange-brown.
What is the chemical formula for ammonium chloride?: NH4Cl.