Isabel's Crystal Formation
Year 9 Science 2013
Thursday 12 September 2013
What is a crystal?
A solid object which is made up of an ordered repeating pattern of the same atom or molecule.
What substances can be used to make crystals?
- Solvent (e.g. water)
- Solute (e.g. rock salt, Epsom salt or sugar)
- A range of chemicals, including but not limited to:
* Potassium alum
* Ammonium chloride
* Sodium borate
* Calcium chloride
* Sodium nitrate
* Copper acetate
What are some examples of crystals in nature?
Snowflakes, diamonds and table salt.
What household items can you also grow crystals from?
Sugar or salt and water.
Explain the process of crystal growth.
Crystals often from in nature when liquid cool down and begin to harden. Particular molecules in the liquid join together as they try to become stable. This happens in a repeating pattern that forms a crystal.
To grow a crystal, there is a different process called nucleation. The molecules of the solute and solvent attempt to stick together, despite other forces in the solution trying to keep them apart. Every so often, a solute and solvent will stay together long enough to attract another molecule and so on until a crystal begins to form.
Explain how crystals can grow in different shapes and sizes.
It can depend on some factors:
- The internal symmetry of the crystal
- The relative growth rates
- The different atoms and molecules making the crystals differs their shape
Outline a few different types of crystals.
Covalent Crystals - has real chemical covalent between all of the atoms.
Metallic Crystals - individual metal atoms sit on lattice sites while the outer electrons from these atoms are able to flow freely around the lattice.
Ionic Crystals - Individual atoms don't have covalent bonds between them but are held together by electrostatic forces.
Molecular Crystals - there are recognisable molecules in the structure and are held together by non-covalent interactions like van der Waals forces or hydrogen bonding.
What effect do crystals have on light travelling through them? (relate to reflection, refraction, dispersion and diffraction)
Crystals are known to polarize light,though they can have the optic results of x-ray diffraction.
What are the optimum conditions for crystal growth?
- Supersaturated solution
- Porous material as crystal foundation
- Warm air temperature to speed growth
- Sufficient light
Tuesday 17th September 2013
* 25g potash alum
* 170mL hot water
*2 x 250mL beakers
- Put 25g of potash alum and 170 mL of hot water in a 250mL beaker. Stir until all dissolved.
Filter the solution through a filter funnel with filter paper inserted into another beaker. Cover with watchglass or fresh filter paper and allow to stand overnight undisturbed. Record level of solution and take photograph.
Wednesday 18th September 2013
-Observe changes in solution. Carefully decant the clear solution above crystals into clean beaker and set aside. Leave the crystals in the other beaker. Allow to stand overnight undisturbed. Record level of solution and take photograph.
Thursday 19th September 2013
- Observe formation of crystals.Using a spatula, transfer a good symmetrical crystal to the beaker containing the decanted solution, aiming to place it centrally. Take a photograph and mark the level of the solution on the beaker. Cover the solution with a loose-fitting paper hat. Allow the beaker to stand undisturbed.
Observation - Tuesday 17th the filtration of potash alum with water is clear, though there is some cloudliness in the solution.
MATERIALS SAFETY DATA SHEET
Chemical Substance - Potash Alum
Describe the substance - Potash Alum is a white powdery substance when solid and dissoles to a clear liquid when mixed with hot water.
Outline any hazards involved with this substance - Potash Alum is harmful if it comes into direct contact with the mouth, eyes, open wounds and skin. It is important the solution is not drunk, spilt or touched by bare skin. When handling the substance ensure that you are wearing goggles, gloves and an apron. If this substance is consumed or touched with bare skin you should seek medical attention immediately as you may get ill.
Safety equipment required at school - Goggles, apron, gloves and closed shoes,
Explain the risks of transporting crystals home - The jar could break and spill its contents and people unaware of the contents of the jar such as family or friends may open the jar and touch or drink the solution.
Outline ways to eliminate risk involved in transporting the crystals home - Ensure the jar lid is secure and place the jar in a plastic bag tied up securely. Make sure the jar isn't knocked around so the solution is not disturbed.
Explain the risks of growing crystals at home - Family and friends could open the jar and come into contact with it and get ill. Also, the jar could break and spill its contents everywhere.
Safety equipment required at home - Gloves and closed shoes.
Explain ways of eliminating risks at home - Place the jar away from food, pets and children in a secure place, for example on a high shelf. Also make sure large labels are placed on the jar so family and friends are aware that it contains a harmful substance.
These pictures are from one week into the holidays. There are less crystals and they are fractured (probably from transportation). Other than this, there hasn't been much change in the crystals.
These pictures are two weeks into the holidays. The crystals don't seem to have changed from the last picture.
Throughout the duration of the experiment, I haven't observed many changes in the growing of my crystals. The process began by dissolving potash alum in hot water and filtering the solution. Then the solution was decanted and the original crystals were placed in a new jar with a portion of the solution. This jar was then left in a stable position for a few weeks. I don't think my crystals grew as effectively as they could have because the jar I placed them in was very different in proportion to the beaker used at the beginning. Also, I could have placed them in more direct sunlight, which I believe would have helped them grow consistently. My crystals were all different sizes, which I think could have been prevented by a smoother transportation from school to home. My crystals do however, show their properties by refracting light and their symmetrical shapes.