Copper tree

Watch a copper tree grow inside a vial!

Difficulty:
Danger:
Duration:
2 days
Copper tree

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

How should I transfer the CuSO4 and NaCl to the vial?

To make it easier, you can use the small funnel from the Starter Kit.

What kind of water should I use?

You can use either bottled or tap water.

I conducted the experiment and let everything sit for two days, but I can’t see any results.

If you can’t find a trace of a copper tree anywhere inside the vial, shake the vial vigorously. Let sit for 30 minutes to an hour. This should help the copper tree grow. If this doesn’t work, repeat the experiment, carefully following the instructions.

I accidentally knocked the vial over. Should I start over?

No, carefully put the vial in an upright position and leave it for two days. The resulting tree may look slightly different – repeat the experiment and compare your results! We recommend you put the vials in a quiet place where they won’t be touched.

How much water should I use after adding the zinc granules?

If you want to count, you should add about 30–40 drops of water. You can also try to experiment a little! Add enough water to cover the crystals completely and write down how much water you added. Then wait for the results. If you aren’t satisfied with the outcome, repeat the experiment using a different volume of water. This way, you’ll be able to pinpoint the optimal amount of water yourself!

Step-by-step instructions

Prepare some wet copper sulfate CuSO4 crystals. They will act as a source of copper.

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Add some table salt NaCl as a separation layer between the copper sulfate and the zinc Zn.

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Add a little bit more water to allow the copper from the copper sulfate to creep upwards towards the zinc. Note the change in color.

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The copper particles (Cu2+ ions) gradually reach the zinc and take electrons from it, turning into copper Cu metal.

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Disposal

Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

Unlike toy bricks or paints, chemical elements do not have predefined colors, and it’s impossible to predict their color by simply looking at the elements’ names. The copper particles  (Cu2+ ions) in copper sulfate CuSO4, for example, are surrounded by water molecules H2. Such a configuration is called a "complex." This Cu2+ complex with water is blue, as you saw at the beginning of the experiment. The chlorine particles—Cl ions  from NaCl—cling more strongly to Cu2+  than the water molecules H2O and replace them easily, forming a new complex of Cu2+ and chloride ions Cl. The green color you saw, as you've probably guessed, is due to this new complex.

Lastly, when the copper ions Cu2+ meet the zinc Zn, they can grab some of its electrons and turn into copper metal Cu. In this configuration, the Cu2+ ions  are surrounded by a cloud of electrons  and other Cu2+ ions. The forming metallic copper Cu is, as you can see, reddish-brown.

Curiously, most metals are silvery-white or grey, and only three metals besides copper feature alternative colors. One is, of course, gold Au. The other two are the extremely reactive cesium Cs, which has a bit of a golden tint to it, and the very slightly bluish osmium Os.

That's interesting!

Why does the copper tree grow?

You already know that the copper tree materializes due to the redox reaction between zinc Zn and the copper sulfate CuSO4 solution. You can even write the chemical equation, and you know how the oxidation states change during the reaction. You also know that sodium chloride NaCl acts as a separating layer for the tree to grow in, as well as to reduce the reaction rate and facilitate the formation of branched crystals. Do you know what else slows the reaction rate? The low concentration of the copper ions Cu2+ that gradually diffuse up from the bottom to the crystal growth zone. All these factors contribute to the low rate of formation of crystal growth points, which gives us the opportunity to grow a big crystal.

The copper tree grows “twigs”  due to new growth points that gradually form on the crystal. These points imply certain directions of growth, and thus the forming metallic copper extends outwards in “branches” instead of precipitating as small, dense crystals or a solid film of copper. And why does the copper tree grow from top to bottom? In scientific language, it correlates to the concentration gradient. Let's take a closer look. Copper sulfate is initially present in the form of a solid salt  at the bottom of the vial. It gradually dissolves, and copper ions  begin slowly moving upward in a process known as diffusion. Over time, the copper ions approach the layer with zinc . The zinc atoms  give electrons to the copper ions, which are converted into metallic copper . Additional electrons accumulate on the small build-up of copper in contact with zinc. As new copper ions diffuse up from the bottom of the vial, they encounter this copper build-up with an excess of electrons and take these electrons from the metallic copper. They then precipitate on the metallic copper in the form of solid metal.