Xmas tree

Grow your own Christmas tree using table salt and paper!

Difficulty:
Danger:
Duration:
12 hours
Experiment's video preview

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the tray.
  • Observe safety precautions when working with boiling water.
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

The salt in the vial didn’t dissolve completely. How to fix that?

If most of salt dissolved, and only a tiny bit of salt is left undissolved on the bottom, you may continue the experiment. There is an excess of NaCl, and the precipitate will not fail the experiment. However, if there is more than 5 mm layer of undissolved salt on the bottom, then there isn’t enough NaCl in the solution to create a fluffy Christmas tree. In that case, we recommend you keep heating the vial a little longer.

The liquid ran all over the Petri dish, and my tree is not soaking.

To soak the Christmas tree in the solution is the most important part of this experiment. Carefully tilt the Petri dish to moisten the tree, but avoid spilling the solution.

Why is it so important to keep the tree undisturbed during the growth of crystals?

Your Christmas tree should be kept still because crystals growing on it are very fragile and may crumble away with a slightest touch.

Step-by-step instructions

Only a limited amount of sodium chloride NaCl can dissolve in water. To start, let’s add a larger quantity of sodium chloride than will dissolve in a vial of water. Add some potassium ferrocyanide K4[Fe(CN)6] so the Christmas tree looks furrier.

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Temperature greatly affects the amount of sodium chloride that can dissolve in water. We will be able to dissolve most of the salt in the vial if we heat the mixture.

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The solution will not readily coat the surface of the Petri dish. In order to make it spread evenly across the bottom, add one drop of a surface-active agent—soap.

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Now put the paper Christmas tree into the solution. Paper is a porous material, so the solution will easily rise and spread through the Christmas tree due to the capillary effect.

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The solution on the Christmas tree and the leftovers in the Petri dish will cool down quickly. The solubility of the salt will decrease, and the salt will start to form crystals again. Moreover, the water will gradually evaporate, and less salt will be able to stay dissolved in the remaining liquid water. As a result, all the salt will gradually settle on the Christmas tree in the form of white crystals. The addition of potassium ferrocyanide will make the crystals more graceful, and the Christmas tree fluffier.

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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

How does our Xmas tree become covered with snow?

We moisten the “tree” with a heated solution of table salt NaCl in water. Water gradually evaporates from the surface of the tree and from the container, which forces the salt to crystallize. Due to the rapid water evaporation, in combination with the effect of potassium hexacyanoferrate K4[Fe(CN)6], the salt from the solution develops into fluffy formations that look similar to snow.

Why does the salt grow in the form of fluffy snowdrifts?

Crystals of common salt NaCl grow into cubes. Their shape is due to a certain orientation of ions – Na+ and Cl – relative to each other. However, NaCl crystals do not always form such a shape upon the evaporation of an aqueous solution. Importantly, the formation of regularly shaped cubes requires that water evaporate very slowly. When the salt crystals grow gradually, their ions have enough time to take their places according to the strict order in a crystal lattice. Conversely, when water evaporates too rapidly, the lattice may turn out “deformed.” The same thing happens with a hot solution. Even though the salt will still form cubes, these cubes will turn out non-transparent, small, and of irregular shape.

In our experiment, potassium hexacyanoferrate (II) K4[Fe(CN)6] causes the shapelessness of our salt formations. Hexacyanoferrate delays the formation of tiny crystals – crystallization nuclei – in the solution, which require the presence of both chlorine and sodium ions. At a certain point, the solution becomes too crowded for the ions, and they promptly leave it. Potassium hexacyanoferrate also influences the way sodium and chlorine ions build these formations. As a result, we obtain fluffy “snowdrifts”, so similar to snow and so unlike cubes.

Why do we add a drop of soap?

Liquid soap is a surfactant substance, and one of its properties is the ability to change the surface tension of aqueous solutions. In our case, liquid soap decreases the surface tension of the solution, so that it evenly distributes in the Petri dish.

The tree has shed. How do I restore it?

One slight shake – and our Christmas tree sheds the salt “snowdrifts”! Luckily, we can easily recreate the beauty! Carefully wash the “snow” off the tree with the same amount of warm water that you used in the beginning of the experiment, and in just 12 hours the “snowdrifts” will grow again! You can repeat the experiment many times.

Can I use another type of paper for the experiment?

The paper you use for this experiment must have a specific consistency. It must be light enough that the salt solution can spread through it uniformly before the fluffy crystals start to form. If this process occurs too slowly or not at all, the salt crystals will start growing right in the Petri dish or only at the base of the paper structure. Meanwhile, it must be thick enough that it can hold its shape when wetted with salt water; paper that is too thin may deform or collapse.

You can easily check yourself whether a paper is suitable for the experiment. Cut out a small piece of your chosen paper, about 1x5 cm in size, and see if it fits the parameters described in the instructions. First, immerse one end of a sample paper in the solution, leaving the other end in the air.

If the paper becomes moistened too quickly, it will rapidly change its shape and collapse. If the paper doesn’t get moistened effectively enough, you’ll know in 12 hours: the “snowdrift” formations will form either only on the base of the tree, or not at all.

If none of these scenarios come true, and the paper turns out covered with salt formations, you can certainly use it in the experiment. You can cut out any shapes (snowflakes, for example), and just in 12 hours they’ll be covered with “snow”!

What other materials can I use instead of paper?

The “snow” in our experiment can be grown on other materials besides paper. For instance, the salt solution would effectively moisten a woolen thread. You can use a metal wire to make a branched “tree,” then tape it around with a woolen thread and use this structure instead of a paper tree. Just make sure the thread gets moistened with the solution.