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Diffusion in liquids

Class practical

This class practical shows that diffusiontakes place in liquids. Students place colourless crystals of lead nitrateandpotassium iodideat opposite sides of a Petri dish of deionised water. As they dissolveand diffusetowards each other theyform clouds of yellow lead iodide.

Lesson organisation

This practical activity takes around 30 minutes.

Apparatus Chemicals

Eye protection.Per pair or groupof students:Petri dishForceps

White tile orpiece of whitepaper

Lead nitrate(TOXIC, DANGEROUS FOR THEENVIRONMENT), 1 crystalPotassium iodide, 1 crystalDeionised waterRefer to Health & Safety and Technical notes

section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection.

Lead nitrate, Pb(NO3)2(s), (TOXIC, DANGEROUS FOR THE ENVIRONMENT) - see CLEAPSS Hazcard.

Potassium iodide, KI(s), - see CLEAPSS Hazcard.

Procedure

aPlace a Petri dish on a white tile or piece of white paper. Fill it nearly to the top with deionised water.

bUsing forceps, place a crystal of lead nitrate at one side of the petri dish and a crystal of potassium iodide at the other.

cObserve as the crystals begin to dissolve and a new compound is formed between them.

Unit 2. Particles and Atomic Structure

Syllabus Ref. 1

http://www.rsc.org/learn-chemistry/wiki/Substance:Lead_nitratehttp://www.rsc.org/learn-chemistry/wiki/Substance:Potassium_iodidehttp://www.rsc.org/learn-chemistry/resource/res00001752/learn-chemistry-health-and-safety-guidancehttp://www.rsc.org/learn-chemistry/wiki/Substance:Lead_nitratehttp://www.rsc.org/learn-chemistry/wiki/Substance:Potassium_iodidehttp://www.rsc.org/learn-chemistry/wiki/Substance:Potassium_iodidehttp://www.rsc.org/learn-chemistry/wiki/Substance:Lead_nitratehttp://www.rsc.org/learn-chemistry/resource/res00001752/learn-chemistry-health-and-safety-guidancehttp://www.rsc.org/learn-chemistry/wiki/Substance:Potassium_iodidehttp://www.rsc.org/learn-chemistry/wiki/Substance:Lead_nitrate

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Teaching notes

The lead nitrate and potassium iodide each dissolve and begin to diffuse through the water. When the lead ions and iodide ionsmeet they react to form solid yellow lead iodide which precipitates out of solution.

lead nitrate + potassium iodide lead iodide + potassium nitrate

Pb (aq) + 2I-(aq) PbI2(s)

The precipitate does not form exactly between the two crystals. This is because the lead ion is heavier and diffuses more slowlythrough the liquid than the iodide ion.

The demonstration A solid-solid reactioninvolves the same reaction but in the solid state.

Health & Safety checked, September 2014

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

Nuffield Foundation and the Royal Society of Chemistry

Page last updated October 2015

http://www.rsc.org/learn-chemistry/resource/res00000507/a-solid-solid-reaction-between-lead-nitrate-and-potassium-iodidehttp://www.rsc.org/learn-chemistry/resource/res00000507/a-solid-solid-reaction-between-lead-nitrate-and-potassium-iodide