Crystal Formation Task


By Lisa Antal


Crystals Questions

A crystal is a solid whose atoms, molecules or ions are arranged in an ordered
pattern. Creating a geometrical shape.

The substances used to make crystals can sometimes be hazardous,
so we try to use substances that are non-hazardous. Some of the substances that
are used to make crystals are bluestone (cupric
sulfate pentahydrate), alum (aluminium potassium sulfate) and Rochelle salt
(potassium sodium tartrate)

There are many crystals found in nature, some examples
are snowflakes, diamonds and salt. Some household items that you can also grow
crystals from include salt, sugar, borax, alum and Epson salt.

Crystals come in all shapes and sizes. depending on what substances you use and how much. If your crystal gets enough sun so that the water has evaporated the crystal will be bigger but if you don't keep it in the optimum growth conditions than it will not grow very big.

Some different types of crystals include cubic - not always cube shaped, hexagonal - six-sided prisms, trigonal - possess a single 3-fold axis of rotation instead of the 6-fold axis of the hexagonal division, tetragonal - similar to cubic crystals, but longer along one axis than the other, forming double pyramids and prisms, monoclinic - like skewed tetragonal crystals, often forming prisms and double pyramids, triclinic - usually not symmetrical from one side to the other, which can lead to some fairly strange shapes.

Because crystals have a high index of refraction they usually have total internal reflection which is shown in the diagram 1. Diamonds are cut specifically so there is a good amount of total internal reflection shown in the diagram 2.dispersion is when the light is refracted too much therefore allowing you to see colour.

Because warmth is the key to forming crystals; the 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; combine them by placing your jar on a warm, sunny windowsill and you should have crystals in a few days.

Materials:

250ml beakers

hot water

filter funnel and filter paper

fine nylon thread

tweezers,tongs, plastic spoon or spatula

ruler

watch-glass or paper hat

smart phone or digital camera and a diary or log book

Method:

Day 1:

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 discarded.

Day 2:

The next day, observe the beaker of solution. The bottom should have become covered with a layer of smallish crystals which formed spontaneously as the solution cooled. 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.

Day 3:

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.

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.

On the holidays:

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.

Observations

Day 1

We dissolved the potash alum and then filtered it into our jars. the solution was clear.

Day 2

We left it overnight and there was only one crystal in our jar so we had to leave it overnight again so more crystals could grow

Day 3

Two more crystals grew overnight, so we each got to take one crystal home in our jars

Day 7

The crystal hasn't grown at all since Thursday. The crystal is still at 0.5 cm small and the solution hasn't evaporated and is still at 5 cm. There is no rate of growth. the crystal is shaped like a hexagon. There are little crystals on the bottom that look like sugar.

Day 15

I have been growing my crystal for 15 days now and absolutely nothing has happened yet. Maybe it hasn't gotten enough sun. The crystal is 0.5 cm and the solution is still 5 cm. There are still little crystals on the bottom of the jar.

Final crystal summary

In this experiment my crystal did not grow at all. In my jar there were about three crystals in it, but the largest crystal in my jar was about 0.5 cm long. The solution in the jar stayed at 5 cm and didn't evaporate at all. There were a little bit of sugary looking crystals on the bottom of the jar. This artwork demonstrates the properties of a crystal by showing the refraction of light.

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