1. What is a crystal?
A crystal is a solid material, that is formed by molecules connecting together in a repetitive, uniform fashion. Unlike many other solids, the collections of atoms (Unit Cells) are formed in the same pattern throughout the entire substance. This allows light to refract and disperse in interesting ways.
2. What substances can be used to make crystals?
A list of commonly used substances when making crystals include:
- Aluminium Potassium Sulfate
- Ammonium Chloride
- Calcium Chloride
- Sodium Nitrate
3. What are some examples of crystals in nature? What household items can you also grow in crystal form?
A very well-known example of a crystal found in nature is the snowflake, which is comprised of many ice crystals. As expected, ice crystals can be made at home with relative ease, if you have water and a freezer. Other examples include: quartz, which is the crystal found in granite; to make crystals at home, it is good to make a saturated mixture of water and salt or sugar. The sugar can be plain sugar, but the salt has to be rock salt or Epsom salts.
4. Explain the concept of crystal growth.
The beginning of crystal is called nucleation. This process occurs when the solute that the crystal will grow in has molecules that are attracted to the other solute molecules in the solutions, not just the solvent molecules. In the right conditions, these molecules will have an attractive force, which will force them together for a little while. However, if they are not forced apart by the other attractive forces in the solution long enough to meet up with another molecule, and another after. Eventually, so many will join together to form the 'critical size', at which point the attraction between the molecules is stronger than the other forces countering them, and this protocrystal (the pre-crystal) will form a nucleation site. This site will then float around the solution, bonding with other molecules and 'growing'.
5. Explain how crystals can grow in different shapes, sizes and colours.
The size and shape depend on two different factors; the symmetry of the inside of the crystal, and the relative growth of different areas of the crystal. The meaning of this that if there are four sides of a crystal, and they have an even rate of growth, then it shall be square. However, if two of these sides grow faster, then the crystal will become a rectangular shape or similar. Crystals can grow in many different shapes, but these are the simplest to explain.
The colour depends on the different chemicals used to form the crystals, and the colours of light that these molecules absorb.
6. Outline a few different types of crystals.
Examples of crystals are cubic (these are not necessarily cubes; they can have eight or ten faces), hexagonal, which forms a hexagon if viewed at its cross section, and triclinic, which do not usually have perfect symmetry from one side to the other, making them appear in weird shapes.
7. What affects do crystals have on light travelling through them?
Though crystals sometimes reflect light, they often refract the light that enters them. This refracted light disperses and this is what causes them to glitter and shine with different colours when moved in light. Often they are shaped so that they refract more effectively, as this is what makes crystals so appealing.
8. What are the optimum conditions for crystal growth?
The best place to grow crystals would be in a warm place, but not in direct sunlight. The temperature needs to be even for the crystal to grow properly, and it is not good to keep it near a heater or where there is a draught.
9. Method and materials for making crystals:
Materials: 2x 250ml beakers, filter papers, hot water, tweezers/tongs/spatula/spoon, covering cloth or hat to cover, watch glass to cover beakers.
Day 1. Place roughly 25 grams of potash alum in a 250ml or larger beaker. Add approximately 170ml of hot water to this, to help assist in the dissolving of the potash. Stir until dissolved. It may appear cloudy, but this is to be expected.
Filter the still-warm solution through filter paper, into a new beaker. Then, cover this beaker with either a new piece of filter paper of a watch glass. It can then be placed to cool down overnight in a sheltered place. NOTE: always clean up everything after you are finished.
Day 2. When observing the solution the nxt day, there should be a sediment on the bottom of the beaker, comprised of smallish crystals. The clear liquid on top needs to be decanted into a different beaker, for later use. If no crystals have formed, you need to 'seed' the solution, using the left over potash alum from the day before. After this is finished, let the crystals stand overnight.
Day 3. Select the best or most symmetrical crystal, and gently remove it with a pair of tweezers, a spoon, a spatula or a pair of tongs. Place this crystal in the beaker with the decanted solution from the day prior, and try and put it in the centre. You can suspend the crystal using a nylon thread and a pencil, but it can just be placed on the base of the beaker.
Take a picture of the crystal to compare with, once the crystal has grown. After this has been completed, place a loose fitting cloth or cover over the top of the beaker, to keep out dust. This is all that needs to be done for the time being.
Observation 1: 19/09/13
Observation 2: 27/09/13
Observation 3: 04/10/13
As part of this assessment, I created a sheet to show the effects of different wavelengths of light on crystals, in terms of the colour they produce. The sheet gives the information necessary to allow them to match the different coloured crystals to their appropriate wavelength. The worksheet can be viewed below.
As the substances involved in this experiment can potentially be hazardous, it is advisable for you and the others around you to be aware of the safety protocol. This protocol can be seen on the sheet below.
OBSERVATION: WEEK FOUR (FINAL OBSERVATION)
These observations can be found on the document with the conclusions, brief bibliography and summary below.