By Melissa Clarke
What is a crystal?
Crystals are a solid material that consists of atoms, molecules or ions that are arranged in an ordered pattern to form different shapes and sizes.
What substances can be used to make crystals?
Salt, Epsom salt, Sugar, Borax, Alum (aluminium potassium sulphate), Photographer's hypo, Bicarbonate of soda (baking soda), Laundry soda and Copper sulphate
What household items can you also grow crystals from?
Alum Crystals- Alum (aluminium potassium sulphate) are the easiest crystals to grow at home. A common compound that is available at the grocery store. Alum is nontoxic and can be used to grow a big, colourless crystal.
Borax Crystals- Borax is a household chemical which can be used to grow colourless crystals and is found in the laundry soap section of the supermarket.
How do crystals form?
The Sodium (Na) and Chlorine (Cl) atoms both share a pair of electrons in an ionic bond. While in the solution, the Na and Cl are separated by water molecules (H20). As the water evaporates from the solution, the Na and Cl atoms begin to bond together, first as single molecules and then the molecules bond together, forming crystals. Every molecule will form the same shape crystal each time it forms. The crystal shape for salt is a cube.
Explain how crystals can grow in different shapes and sizes:
Size and Shapes-
Cubic or Isometric - cubed, octahedrons (eight faces) and dodecahedrons (10 faces).
Tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms.
Orthorhombic - like tetragonal crystals except not square in cross section (when viewing the crystal on end), forming rhombic prisms (two pyramids stuck together).
Hexagonal- six-sided prisms. When you look at the crystal on-end, the cross section is a hexagon.
Trigonal- possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division.
Triclinic - usually not symmetrical and have unusual shapes.
Monoclinic - like skewed tetragonal crystals, often forming prisms and double pyramids.
Different types of group crystals
Isometric- Isometric crystals are formed with the same lengths along all axes. They can have four faces (cubes), eight or ten, all of equal sizes.
Hexagonal- These crystals have six flat faces of the same size. When cut in half, the cross-section of these crystals will form a hexagon.
Covalent Crystals- These crystals have covalent bonds between all the molecules that make them up, meaning that electrons are shared between bonded molecules. These can be looked at as one giant molecule, and they typically have very high melting points.
Ionic Crystals- The molecules in these types of crystals are held together by electrostatic forces. They are very hard; one example of this type of crystal is common table salt.
Molecular Crystals- These types of crystals are very soft, as opposed to other types of crystals. This is because their bonds are noncovalent and weak, such those formed with hydrogen.
Different types of crystals-
>Ammonium Phosphate Crystals
>Calcium Copper Acetate Hexahydrate Crystals
>Copper Acetate Monohydrate Crystals
>Copper Sulphate Crystals
What effect do crystals have on light travelling through them?
It moves like wave and exchanges energy and momentum like a particle. When waves move through a crystal they diffract Light, sound, neutrons, atoms and electrons are diffracted by crystals.
What are the optimum conditions for crystal growth?
-Cover the solution with a loose-fitting paper hat that permits water to evaporate slowly whilst keeping out dust.
-Allow the solution to stand in a draft free location, not in direct sunlight or near a heater. The aim is to keep the temperature as constant as possible.
1. Place approximately 25 g of potash alum in a
beaker (250 ml or bigger) and add approximately 170 ml of hot water.
2. Stir the mixture until all the crystals have
dissolved. (NOTE: don’t use all the alum you have been given –
keep a few crystals back in reserve in case you need to “seed” the solution
3. Filter the warm solution through a filter funnel
into another clean beaker.
4. Cover the beaker of solution with the watch
glass or fresh filter paper and set aside in a cool sheltered place and allow it to stand undisturbed overnight.
(The first beaker and funnel can be washed and
dried and the residue and filter paper used for filtration discarded).
1. Observe the beaker of solution. The bottom should have become covered with a layer of smallish crystals which formed naturally as the solution cooled.
2. Carefully pour off the clear solution above the crystals into a clean beaker and set it aside for later, leaving the crystals behind in the other beaker. If for any reason, no crystals have formed after leaving the solution to stand overnight, the solution can be “seeded” by adding a crystal from the original alum).
3. Let it stand overnight again and observe the
formation of crystals.
1. If nothing has happened, crystal growth may also be made by scratching the bottom of the glass beaker with a glass stirring
2. Choose one good group of crystals needs to be selected to act as “seed” for your big crystal.
3. Using a plastic spoon, spatula, tongs or tweezers, transfer the selected crystal to the beaker containing the decanted solution, trying to place it centrally in the beaker.
(A good technique to promote uniform growth is to suspend the crystal with a nylon thread tied round a stirring rod or pencil resting on the rim of the beaker. This step is not essential, however, and good a crystal can usually be obtained just by leaving the crystal on the bottom of the beaker).
4.Take a picture of the crystal, preferably close to a ruler so that you can measure its size, and mark the level of the liquid
in the beaker. Record the date in your diary
5. Cover the solution with a loose-fitting paper
that permits water to evaporate slowly whilst keeping out dust.
6. Allow the solution to stand in a draft free location, not in direct sunlight or near a heater. (The aim is to keep the
temperature as constant as possible).
·Once a week record in your diary the level of the solution in the beaker and if possible, take a picture of it close to a
ruler so that you can estimate how much it has grown. Try and avoid touching
the crystals during the growth phase as this may induce additional crystals to
·If small isolated crystals appear, you may be able to carefully remove them with tweezers. Be careful not to disturb your big crystal. If small crystals grow on the main crystal remove it, dry it with tissues, and carefully remove the adhering buds. Do not touch the crystal with your fingers. The crystal is likely to be quite fragile, fairly brittle, and easily damaged, so should not be dropped or bumped.
· Sometimes, small crystals can re-dissolve (go back into solution) if the beaker is very gently warmed in a bath of warm to hot water.
1.In this case, your large crystal should be carefully removed from the beaker and gently laid on some tissue.
2. The solution should be stirred very gently, whilst being gently heated up in the water bath.
3.The beaker should be removed from the hot water bath immediately the small crystals have dissolved.
4. Allow the beaker to cool back to room temperature (1 to 2 hours, say) before returning your big crystal to solution.
5. Set the beaker aside under its paper hat and continue to allow the crystal to grow.
6. Continue to monitor progress by reporting on the drop in water level, and estimate the size of the crystal.
If no further growth is apparent;
·A new saturated solution may be prepared as before (dissolving the crude alum in warm water, filtering off any impurities,
and decanting the solution after it has cooled overnight).
·When the new solution is cool enough, your crystal may be transferred into this new solution and may then continue to grow
as it takes up more of the aluminium potassium sulphate salt from the solution.
To terminate the experiment (after about 10 weeks or so)
1.Remove your crystal very carefully from the beaker, dry it with tissues and with a ruler measure its length, width and height.
2.Compare the measurement, if you can, with the size of the original crystal.
3. Take a photo of the completed crystal (next to a ruler to confirm the size)
Tuesday- From what I observed after my group and I putting the ingredients into in the beaker, it looked like a beaker with water in it with a watch glass on top to prevent dust particles of getting inside. We put in on the shelf by the window overnight and see what happens.
Wednesday- The next day, we looked in our group's beaker and on the base we see 4 crystals that were the size of a 5 cent coin. Our group was quite impressed with the overnight results.
Thursday- The following day we looked at the crystals and had 4 crystals and then we divided the crystals evenly and put them into our own separate jars and took them home that night and take care of them over the 2 week holidays.
Day One: Thursday
The beaker had the liquid solution and my 2 small crystals.
Day Two: Friday (following week)
The beaker had several mini crystals bunched up together on the bottom and along with my 2 crystals. Crystal one is The liquid decreased in level by 3 millimetres.
Day Three: Thursday (following week)
The beaker is exactly the same from Friday's observation but the liquid levels dropped by 2 millimetres.
Below is all the photos I took throughout the whole science project: