In this Instructable, we will learn about super saturated solutions, and how to create crystals from them.
(Pictured above is an Alum crystal made using the explained method)
Step 1: Understanding the Science
What happens when we dissolve salt in water? We add a few spoons, keep stirring till all the salt disappears. Salt, here, is the solute and water, the solvent. Together, they form a solution. There is a point when a solution contains more solute than the solvent can dissolve. This solution is known as a supersaturated solution. You normally cannot see the solute in a solution because it is fully dissolved. You are able to see the solute in a supersaturated solution because all of the solute doesn't fully dissolve into the solvent.
Here is a nice graph that I found online, when I was learning more about solutions. We can clearly see that solubility of a particular salt is directly proportional to temperature.So now, we will use the concept of dependence solubility of a solution on temperature to create crystals!
(Please refer: http://chemicals.etacude.com/s/more/nacl.html)
Step 2: Materials Required
You will need the following to start our experiment:
1. A pair of gloves (optional, but recommended when dealing with salts like Borax)
2. Any salt soluble in water. I have used Borax here. Alternative salts that could be used are Alum, Magnesium Sulphate etc,
3. A cylindrical container, preferably transparent, so it would be easier to check progress without disturbing the system
4. Food colouring! (optional)
5. Water and a vessel that can be used to boil water
6. A scale (just a stick would do), some thread and a pair of scissors.
7. A sieve (optional)
With all this ready, lets move on!
Step 3: Getting the Solvent Ready
Firstly, measure 3/4 of the cylindrical vessel with water (here water is the solvent). Pour the contents into another vessel, one with which we can boil the water. Now, heat the vessel till boil.
Science here: In this step, we boil the solvent in order to increase the solubility of the salt in the solvent, i.e. to create a super saturated solution, which dissolves more salt than at just room temperature.
Step 4: Adding the Solute
Before handling with corrosive / dangerous salts, it is advisable that you glove up!
With a spoon, contentiously add salt to the boiling water. Please note, after the water starts to boil, do not switch of the flame, but leave it in sim and continuously stir will adding the salt.
Science here: There will be a point where you cannot add any more salt and the solution cannot accept any more salt. At this stage, the solution has reached saturation at its elevated temperature, but is at super saturation with respect to room temperature!
After this, switch of the stove, and a SMALL pinch of food colouring of your choice. I haven't done so here, but used green food colour in making those cool Alum salt crystals you saw in the thumbnail.
After doing so, pour the solution from the boiling mixture back into the cylindrical tumbler, through sieve, just to make sure no solid particle passes through.
Step 5: Setting the Core
Once you are done with all the above steps, take a piece of thread of adequate length, and tie it up to the scale / stick as shown. Dip the thread into the solution with the scale supported by the vessel (as shown). It does not matter if the thread floats, but push it in as much as you can.
After doing so, leave the setup at an undisturbed place overnight. By undisturbed, I mean away from vibration.
Science here: The reason we do this is to provide a core foe the crystals to form around; similar to what dust particles do in clouds.
Step 6: Fruits of Labour
After leaving the setup undisturbed for a while, it can be noted that a crystal has grown around the thread! Magical! Now remove the thread from the scale, cut off the excess and create your own crystal garden!
Science here: The reason we let the super saturated solution cool is, because while doing so, the temperature decreases and in turn, reduces the solubility of the solution. So the salt that would dissolve in the solute at a higher temperature, now have nowhere to go, as solubility decreases, so the crystallize out of the solution around the thread (like clouds). This is a gradual and slow process, that is why it is not advisable to store the solution in a fridge to cool, but best left at room temperature. Also, if there are any vibrations / shocks, it would disturb the crystal formation. So, no vibration means better and larger crystals!
You are now endowed with the secret knowledge and science of making super cool crystal! So what are you waiting for? Go ahead and start making 'em!
Arty tip: Use red colour food colouring to make red crystals, and instead of thread, use tin bent in the shape of a heart! You now have a red crystal shaped heart! ( I made this for my mom on mothers day and she loved it :-) )