#melchemistry

This experiment is another example of a single displacement reaction where a more active metal displaces the less active one from its solution. This time performed on a filter paper to reveal the beautiful copper crystals in a shape of a tree and thus called dendrites. 

For this experiment you’ll need a 10% solution of a copper sulfate, a filter paper in a dish (like a Petri dish) and some pieces of metals. A zinc pellet or a piece of iron is good (both metals are more active than copper). It’s also possible to use different metals and compare the result. There intensity of dendrite growth will depend on the metal activity.

If you have a MEL Science subscription, you might already have a dish and a zinc pellet from the “Tin” set and a copper sulfate from the “Metal contest” set. To make a solution, dissolve a half of a big measuring spoon of copper sulfate in 10 ml water. As for filter paper, you can take any paper that absorbs water. A coffee filter or even a paper kitchen towel. As for the pieces of metals, try a paperclip, a nail, a pin or even a hedgehog from the “Tin hedgehog” experiment. Just take into account, that paperclips may be made of different metals, not only iron. And steel (mostly iron) nails, pins and paperclips may be covered with a thin layer of zinc. It is not a problem for this experiment. Make sure that the metallic object has a flat side to make good contact with a filter paper.

The instructions are easy. Place the filter paper into a dish and moisten it with the 10% copper sulfate solution. Not too much, just make it all wet. Place the pieces of metal on the filter paper. Make sure they touch the paper. Cover the dish and wait for some hours (or leave it for the night). Observe the brownish dendrites of metallic coppers grown around the piece of metal.

In case of several pieces of different metals, the result will reflect the metal’s reactivity to some extent.

In general, the more active metal (see the reactivity series), the more dendrites should grow and the farther they reach. But even there is a correlation between the metal’s reactivity and the amount of dendrites, there are still other factors to consider. Like the size of the pellet, its purity, its ability to form a protective layer of oxides (which prevents the reaction), contact between the metal surface and the solution on the filter paper etc.

You may also like to watch the MEL Science version of this experiment (see instructions in the video description on YouTube):

MEL Science suggests to look at the single displacement reaction as a sport competition where the metals are athletes. In this contest the more active metal replaces the less active one in a solution. And the “strength” or reactivity is pre-determined and arranged in a reactivity series.

In their experiment from the “Metal contest” set they suggest to observe how more active zinc replaces copper from copper (II) sulfate solution and tin from tin (II) chloride. You can find the detailed instructions and explanation on their webpage.

An easy way to observe a single displacement reaction. There is not much to add, so here is what I got:

The reactivity series gives a lot of combinations to experiment with, so there is more to come. And  at risk of preempting myself, let me tell you that not all of them will go as expected.

Like on this video you can clearly observe gas bubbles as a result of a secondary process. Both copper (II) sulfate and tin (II) chloride tend to hydrolyse in a solution and form acidic environment (sulfuric or hydrochloric acid):

Cu2+ + SO42- + HOH ⇄ CuOH+ + SO42- + H+ 

Sn2+ + 2Cl- + HOH ⇄ SnOH+ + Cl- + H+ 

This is an example of a displacement reaction. A more active element displaces a less active one from its salts. In case of metals there is a reactivity series where all metals are arranged by their activity from the highest to the lowest (vertically or horizontally).

A short example of reactivity series looks like:

K→Ca→Na→Mg→Al→Zn→Fe→Co→Ni→Sn→Pb→H→Cu→Ag

Potassium is the most active in this particular example and silver is the least one.

For a full version, please, visit a Wikipedia article on reactivity series.

In this experiment zinc as a more active metal displaces tin from a solution of tin chloride. Metallic tin is disposed on a zinc pellet and forms beautiful crystals. A tin covered zinc pallet might remind you of a hedgehog. Or a lovely frosted pine tree (with help of a macro lens).

The reaction can be written as:

SnCl2 + Zn → Sn + ZnCl2 

Addiction of acid to tin chloride solution is needed to suppress its hydrolysis in water. Normally a hydrochloric acid is used for a chloride salt, but other strong acids will do too. Even an acidic salt like sodium hydrogen sulphate (which is safer to work with than an acid).

I performed this experiment with the help of MEL chemistry “Tin” set. In their sets they provide all materials needed to perform 2 or 3 experiments.

On their page you can find more detailed explanation of this experiment: 

https://melscience.com/en/experiments/tin-hedgehog/

And this is how my “tin hedgehog” looks like after 15 minutes: