Homeschooling with MEL Science: Growing Tin Dendrite

Once a week, on a Tuesday afternoon, Abigail and I get together and do some science together. Usually it is from a company called MEL Science, with whom we have a monthly subscription (Abigail’s Christmas present this year). Last week we began with growing a tin hedgehog. The second activity we did was to grow Tin Dendrite.

Growing Tin Dendrite: The Box

Abigail is sent one box per month which contains at least two different activities with absolutely EVERYTHING included that you need to carry them out (more than once, should you wish to!):

Each box it themed (click on the link to see all the available MEL science chemistry kits). For example, Abigail’s first box was tin themed. Both experiments used the properties of tin – in this case growing tin dendrite trees in a petri dish, using the dendrite appearance of tin crystals which form when an electric current is passed through a solution of tin chloride. And last week’s activity: growing a tin hedgehog (tin creates spiky crystals, which look hedgehog-like!) . Today, I will be sharing photos of Abigail making a tin dendrite tree.

Growing Tin Dendrite: Preparations

To prepare for each experiment, I first have Abigail watch the video supplied by MEL Science (all MEL science experiments). The company provides simple experimental videos, along with instructions on how to carry out the experiment; safety aspects related to the particular experiment; Step by step instructions; expected result; an easy to follow scientific explanation of exactly what is happening and suggestions for further study. Abigail watches and reads through the entire Tin Dendrite information page.

Afterwards, she gets everything she needs to do the experiment ready, along with all her safety equipment (goggles, lab coat, gloves etc):

Growing Tin Dendrite: Method

Even though Abigail reads through the website instructions and watches the video first, there is a handy step-by-step booklet which comes with the experiment set, which she always follows:

Firstly, Abigail prepares the tin chloride solution by adding the sodium bisulphate to the tin II chloride:

Which she then shakes to mix:

Next, she pours the bottle of prepared tin chloride solution into the petri dish:

As you can see, it doesn’t cover the whole of the base:

Abigail adds two drops of liquid soap:

This breaks the surface tension allowing the solution to spread out more easily, thus covering the bottom of the petri dish:

Abs attaches the electrodes to opposite ends of the petri dish:

And attaches the electrodes to the battery set:

Lastly, my little scientist ooohs and aahs at the miracle of growth which is happening at a remarkably quick speed:

Growing Tin Dendrite: Results

These grew almost immediately:

I had to snap away very quickly just to capture the progression:

And as such I only managed to get three pictures, so quick was it!

Growing Tin Dendrite: What is happening

When Abigail attached the crocodile clips to the petri dish she created a connection between the batteries and the tin II chloride solution. Once the electric circuit is completed, the electric current begins to flow through the solution. This causes a tin reduction to occur near to the clips, precipitating solid tin:

Sn²⁺_(solution) + 2e^–→ Sn_(solid)

The tin continues to grow as dendrites, spreading in the same direction as the electric current is flowing: from one clip to the other.

For a more comprehensive explanation do visit the MEL Science experimental page

Growing Tin Dendrite: Further Exploration

There are many ways to extend this experiment, and we will probably return to it another week (so this post may be added to as and when we do more). However, on this occasion Abigail chose to explore its disappearing properties. She changed round the crocodile clips thereby changing the direction the electric current flows in. The dendrites disappear and then start growing in the opposite direction: