Silver Crystals Through Electrolysis

5 Experiments on Structure-Property Relationships E5.1 Silver Crystals Through Electrolysis 

Problem Metals cannot easily be visibly crystallized because they form very small crystallites and thus arbitrary conglomerates. Sometimes, zinc crystals can be found on polished zinc posts that look like ice flowers on a window-pane. One often finds beautiful rainbow-colored crystallized cubes of crystal 

Material Glass bowl, alligator clips, cable cord, iron wire as electrodes (take combustion spoons), 10-20 V source (or serially connected batteries) dilute silver nitrate solution, concentrated ammonia solution. 

Procedure Add few milliliters of ammonia solution to approximately 100 ml silver nitrate solution until the initially formed precipitate dissolves. Place the solution in a glass bowl. Fix two iron wires in such a way that one wire is in the form of a round electrode dip the other one, the negative electrode, at the middle of the bowl. Apply a voltage of 10-20 V DC to the electrodes. 

Observation Cascades of crystals form from the central electrode silver crystals (see also Fig. 5.2). 

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The fact that pulverized metal crystals generally turn black should perhaps be shared with students. An electrolysis of a silver nitrate solution with DC voltage leads to a deposition of black metal lumps. The metal forms silver crystals only when the concentration of free silver ions is strongly reduced through stable complexes, i.e. when the silver nitrate solution is mixed with sodium cyanide solution or with ammonia solution. 

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