Year 9 Science
What is a crystal?
Crystals are solids that form by a regular pattern that is repeated. It is pattern of connected molecules; the unit cell is a collection of atoms that is repeated in exactly the same arrangement, throughout the whole crystal. They can look interesting and form unique shapes naturally.
What substances can be used to make crystals?
Substances used to make crystals are: Sugar, salt, alum, and borax.
What are some examples of crystals in nature? What households items can you also grow crystals?
Crystals in nature include rocks and ice. Crystals in households can include diamonds, sugar and salt.
Growth of a crystal?
The process of crystal forming is called crystallization. Crystals often form in nature when liquids cool and start to harden. Certain molecules in the liquid gather together as they attempt to become stable. They do this in a uniform and repeating pattern that forms the crystal. In nature, crystals can form when liquid rock, called magma, cools. If it cools slowly, then crystals may form. Many valuable crystals such as diamonds, rubies, and emeralds form this way.
can crystals grow in different shapes, sizes, colours?
Crystals can have very flat surfaces called facets. They can form geometric shapes such as triangles, rectangles, and squares. The shapes are a direct result of the type of molecules and atoms that make up the crystal. Smaller crystals and larger crystals that were formed of the same molecules and in the same method should have similar shapes. There are seven basic crystal shapes, also called lattices. They are Cubic, Trigonal, Triclinic, Orthorhombic, Hexagonal, Tetragonal, and Monoclinic.
Types of Crystals
Single Crystals, Poly Crystals, Liquid Crystals, these are the three basic types of crystals.
What are the optimum conditions for crystal growth?
Warmth is key to forming crystals, warm air temperature causes the water to evaporate and form the crystal. The warmth causes the crystal is grow faster. Crystals will still grow in cooler temperatures, but it will take much longer. The growth of the crystal also requires light, the crystal will eventually grow in darkness but it works much faster in light.
- beaker x2
- filter paper
- Place approximately 25 g of potash alum in a beaker (250 ml or bigger) and add approximately 170 ml of hot water.
- Stir the mixture until all the crystals
have dissolved. The solution may have a slightly cloudy or milky appearance due
to impurities in the technical grade of alum used.
- Filter the warm solution through a filter funnel (in which filter paper has been inserted) into another clean beaker.
- 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 can be thrown away.
Observe the beaker of solution. The bottom should have become
covered with a layer of smallish crystals.
- 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. -- Let it stand overnight again and observe the formation of crystals. Alternatively, if nothing has happened, crystal growth may also be induced by scratching the bottom of the glass beaker with a glass stirring rod.- From the bed of crystals, one good symmetrical crystal or group of crystals needs to be selected to act as “seed” for your big crystal. 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.
- Take a picture (if possible) 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.
- 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.
Once a week record in your diary the level of the solution in the beaker and if possible, without disturbing your crystal, take a picture of it close to a ruler so that you can estimate how much it has grown. Try and avoid disturbing crystals during the growth phase as this may induce additional crystals to grow.
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 be encouraged to re-dissolve (go back into solution) if the beaker is very gently warmed in a bath of warm to hot water. In this case, your large crystal should be carefully removed from the beaker and gently laid on some tissue.
- The solution should be stirred very gently, whilst being gently heated up in the water bath.
- The beaker should be removed from the hot water bath immediately the small crystals have dissolved.
- Allow the beaker to cool back to room temperature (1 to 2 hours, say) before returning your big crystal to solution.
- Set the beaker aside under its paper hat and continue to allow the crystal to grow. Continue to monitor progress by reporting on the drop in water level, and estimate the size of the crystal.
After day one we came back and no crystals had been formed, therefore we had to make it again.This attempt was also unsuccessful so we shared the crystals around from other classmates and ended up with one larger crystal and lots of tiny ones in the solution (2cm). We took this home of the holidays.
The crystal remand the same throughout the holidays, the liquid measurements stayed the same and crystal size.
The main Crystal has stayed the same size and shape, although the smaller granules around it have started to clump together, and another larger crystal has to started to form off the gramule clumps. The solution measurements are the same (2cm high)
Over the weeks my crystal has not grown much, the main crystal stayed the same size, but all around it granules started to form which looked like sugar. Towards the end the granules started to develop into clumps but were less than a 0.5mm in height. in the last couple of days a small crystal developed off a clump of granules, but it was small and thin.