Isobella G - Yr 9 science 2013
What is a Crystal?
A crystal is a build-up of chemical compounds that joins together in a constant arrangement allowing light to bounce off them. These chemicals form a solid substance which can be microscopic or quite large.
What Substance can be used to make crystals?
Aluminium potassium sulphate dodecahydrate, ammonium chloride, borax and calcium chloride.
What are some examples of crystals in nature? What household items can you also grow crystals from?
Nature: Snowflakes, diamonds
Household items: table salt, sand
Explain the process of crystal growth?
Sodium and Chlorine atoms both share a
pair of electrons in an ionic bond. While in solution, the Sodium and Chlorine are
separated by water molecules. As the water evaporates from the solution, the Sodium and Chlorine 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 like a six-sided die.
Explain how crystals can grow in
different shapes and sizes?
Crystals can come in other shapes than just cubes. For example, you can see triangle shapes in crystals like rubies and amethysts. The unit cells for these crystals
are more difficult than in salt and they have a different shape, but the unit cells still stack together in a regular pattern to make a crystal. Perfect crystals have only straight edges, but most of the crystals we see in nature aren't perfect. They often grow in confined spaces in the ground and don't have the room to grow in even directions. So they may have some straight edges, but look rounded or jagged in other places.
Outline a few types of crystals?
Diamonds, rubies, sapphires, and emeralds have been a popular type of
crystal for thousands of years. They are highly valued due to their beauty and
relative small amounts that exist in nature. There also opals which is an
Australian crystal, not so rare in the outback. Plenty are gathered each week.
Salt is used in day to day cooking and cleaning. Sugar is used in cooking also.
What effect do crystals have on light travelling through them? (Relate
to reflection, refraction, dispersion and diffraction)
Light behaves differently depending on which
direction the light is reflecting at the crystal. The index of refraction
depends on both composition and crystal structure. When light hits a crystal at
a certain point, there will be a reflection of bright light. In some
circumstances the light can be quite blinding, but it depends on the crystal.
What are the optimum conditions for crystal growth?
Warmth is the key to forming crystals. A
jar's surroundings should be warm also for optimum crystal growth. Warm air
temperature helps water evaporation, causing the crystals to grow more quickly.
Crystals will still grow in cooler temperatures, but it will take much longer
for the water to evaporate. Crystal growth also requires light. Again, the
crystals will eventually grow in the dark, but it will take a very long time.
Light evaporates water as heat does; if you put a jar of what you are using to
make your crystal you should have crystals forming in a minimum of a few days.
Making The Crystals!
25 grams of potash alum
2x 250 ml beaker
170 ml of hot water
watch glass/more filter paper
Step 1 Place approximately 25 g of potash alum in a 250ml beaker
Step 2 Add 170ml of hot water
Step 3 Stir the mixture until the crystals have dissolved, the solution may be slightly cloudy which is perfectly fine.
Step 4 Filterthewarm solution through a filter funnel (with the filter paper inserted) into the second clean beaker.
Step 5 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.
Step 6 The first beaker and funnel can be cleaned and dried and the waste and filter paper can be thrown out.
2x 250ml beaker
(left over potash alum)
loose fitting paper hat
Step 1 Observe the beaker containing the solution. The bottom should be covered with a small layer of crystal because the solution is cold.
Step 2 Gently decant (pour off) the clear liquid above
the crystals into the clean beaker and set aside. Make sure the crystals are
left in the other beaker. If no crystals have formed overnight, you can seed
the solution. Do this by adding crystals from the original alum and let it sit
overnight again. You may also need to stir the solution with your stirring
Step 3 Choose one good symmetrical crystal or group of crystals to act as the ‘seed’ for your large crystal. Using your plastic spoon, tweezers, tongs or spatula transfer the chosen crystal into the middle of the beaker with decanted solution.
Step 5 Take a picture of the crystal in line with the ruler so you measure its size and mark the level of liquid in the beaker.
Step 6 Cover the solution with a loose fitting paper hat that allows water to slowly evaporate and keep out foreign particles. Keep it somewhere where the temperature will stay constant.
2x 250ml beakers
Step 1 Once a week record the level of liquid in the
beaker and without moving the crystal take a photograph of it next to the
Step 2 Estimate and record how much the crystal has grown.
Step 3 If any isolated crystals appear you can remove them gently with tweezers. If small crystals begin to form on your main crystal dry and remove them with a tissue.
Step 4 If the crystal isn’t growing anymore you can create a new solution using the pervious steps and gently transfer the crystal once the solution is room temperature. The solution may need to be left overnight to cool before the crystal is added.
Step 5 Once the experiment is over, remove the crystal extremely carefully from the beaker, dry it with a tissue and measure its length, width and height with a ruler. Compare the measurement to the original size of the crystal in your logbook.
Today my group completed the practical component of the experiment! We gathered the potash alum, combined it with hot water and filtered the solution into a clean beaker correctly so hopefully tomorrow we will have some crystals beginning to grow.
Today my group had an observation of our crystal jar solution and found out that it had formed around 6 small clear crystals! We then divided them up in to 3 jars with the aluminium potassium sulphate. We used these crystals we made to form other crystals this worked like a seed.
After 3 days my crystal has grown up to 9 mm! I have placed the crystals at home on my desk. Below is a photo of my crystal.
It is my second time recording my observations on my crystal at home. I have left the filter paper hat on top of the jar allowing some air to enter and leave the jar.
Since last week a lot of water had evaporated and smaller crystals have begun to appear surrounding my main crystal on the floor of the jar.
It is now day 14 and my crystal growth has progressed further! It has now grown an extra 1.2 cm! I am really happy with the results so far, and now the soloution level has dropped and is now 1 cm deep. Below is a photo with my results
Above: Crystal growth Below: solution that is left
It has been almost a week since I have observed my crystal experiment and my crystal growth process has slowed dramatically! My solution has stayed the same at the height of 1cm and my crystals have not changed. I believe that due to the lack of sunlight my crystals have gotten over the past 6 days has affected my growth and evaporation in this experiment. I am now going to put them on my window ledge in direct sunlight and see what happens.
5 days later I have noticed a huge difference in my crystals as I have left them in direct sunlight. Most of the solution has now evaporated and my crystal is growing larger and larger!
I am very pleased to say that my liquid solution has nearly evaporated and the large crystals in my jar have grown even more since I last recorded my observations! These photos down below show that in the next few days the liquid will be completely dried up and I will be able to take photos of my crystals out of the jar.
All of my liquid solution has evaporated! There are also some small rings of tiny crystals at around the base of the jar where the solution level would have been at one stage! my crystal is holding up alright.
Overall my crystal experiment was successful from the very start. My group worked corporately to form a good solution in class. I mamaged to grow my crystal 5 cm long in the duration of the experiment. As well as completing a successful prac I had so much fun with a very different, more hands on experiment! The final dimension of my largest crystal was 5cm and it is located under the clump of crystals below.
Below this creative photograph shows many dimensions of the different crystals. I placed my largest crystals together in a clump as they broke when I had to get them out of the jar. The light is reflecting off the crystals onto one another and into the centre of them projecting light and giving them a mirrored effect. They are clear glistening crystals.