Make a Chemical Garden From Cat Litter, Drain Opener, and Root Killer

In this video we're going to use silica in crystal cat litter, sodium hydroxide in drain opener, and copper sulfate in root killer to make the famous chemical garden experiment.Show more

Get 60g of silica gel based cat litter. This is often called "crystal cat litter". Add to it 30g of sodium hydroxide and 100mL of water. The reaction will get hot so be careful. This reaction forms sodium silicate. You may have to leave it overnight if it goes slowly. But few grains of leftover cat litter is acceptable.

Dilute the mixture by adding another 800mL of water. This cannot be added earlier as the mixture must be highly concentrated to successfully make sodium silicate.

Thoroughly mix the solution.

Now drop in a dozen large crystals of copper sulfate (around 1-2cm size). It's recommended to separate them for best looking results.

Over the course of two days the crystals will seem to sprout and grow as the reaction progresses.

What's happening is quite fascinating. As soon as you drop the crystals in, the surface of the copper sulfate dissolves but immediately reacts with the sodium silicate solution to form solid copper silicate. This coats the crystal so it's encased in a layer of copper silicate. But the silicate layer isn't perfectly impervious or rigid, water can still diffuse in. As it diffuses in it dissolves the copper sulfate underneath and forms a solution. This concentrated solution pushes out as the water continues to diffuse in and increases in pressure. The copper silicate membrane bulges out but eventually it can't contain the pressure and ruptures. The copper sulfate solution rushes out of the rupture and instantly reacts with sodium silicate solution to form another layer of copper silicate.

This layer is newer and weaker so as the pressure builds again it too will rupture and the process repeats. This gives the appearance of a growing structure. It grows upward because the density of the copper sulfate solution is lower than that of the sodium silicate.

Overall this looks like a growing stalagmite of copper silicate.

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