Crystal

Crystal Formation Task

Questions 1-8

What is a crystal?

Crystals are a solid that form by a regular repeated pattern of molecules connecting together.

What substances can be used to make crystals?

Alum Crystals: Alum is a kitchen ingredient that can be grown as crystals simply by mixing alum in boiling water until no more will dissolve.

What are some examples of crystals in nature? What household items can you also grow crystals from? The most common crystal you will find in nature are snowflakes and diamonds. In most households you will find table salt, which is actual a form of crystal! It is easy to make a crystal at home, for example you can make a simple crystal by using table salt, sugar, or epsom salts and water.

Explain the process of crystal growth Crystals grow by a process called assisted nucleation. The starting material (solute) dissolves into the water (solvent) a solution is created. The solute molecules float around in the water but aren’t able to meet each other properly as they need a meeting place where they can join together. By placing a piece of string into the solution a plane is provided for the solute building blocks (atoms and molecules) to meet and join together.

Explain how crystals can grow in different shapes and sizes

Crystals grow in certain shapes and sizes because the atoms/molecules join and create a pattern that repeats itself to make a particular shape. A crystal grows by adding atoms/molecules to all of its sides in the exact pattern as the atoms and molecules that were added before. Because the atoms and molecules are different in each crystal, they all have different shapes and sizes.

Outline a few types of crystals:

Borax Crystals: You can grow borax crystals around any shape you like or you can use them to sprinkle a crystalline coating onto any porous object.

Suger Crystals: are easy to make and edible

Ionic Crystals:This is a crystal where the individual atoms don't have covalent bonds between them, but are held together by electrostatic forces. An example of this type of crystal is sodium chloride (NaCl). Ionic crystals are hard and have relatively high melting points.

What effect do crystals have on light travelling through them? (Relate to reflection, refraction, dispersion and diffraction) Crystals have a high refractive index, so light inside them is bent and travels slower then in the air. Since crystals have a high refractive index

What are the optimum conditions for crystal growth? Crystal growth is quickest when in a hotter climate and it is important to keep the crystal still, because vibrations can slow the process.

Method:

What you need:

-Potash alum

-Beaker

-Hot water

-Filter funnel

-Spatula

-Stirring rod (optional)

-Ruler

-Loose-fitting paper hat

Day 1:

Place approximately 25 g of potash alum in a beaker (250 mL or more) 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 (which the filter paper has been inserted into) into another clean beaker. Cover the beaker of solution with the fresh filter paper and set aside in a cool undercover 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 thrown away.

Day 2:

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 decant (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.

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.

(NOTE: 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.

Over 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.

Crystal Preparation

Tuesday: We poured the hot water into the beaker and mixed till it dissolved. The we got the solution and filtered it through the funnel. We finally left it in the classroom with filter paper covering it.

Wednesday: On the second day no crystals had formed in the jar, so we had to repeat the day 1

Thursday: This time we had one crystal in our beaker, so we had to get two more from another group. We evened out the solution and carefully put the crystals from our beaker into our own jars to take home.

Crystal Growth

Week 1: The jar was placed on the chest of draws wear it is dry and has a low chance of being nocked. The solution was at 1.5cm and the the crystal was at 2cm. The water was clear and there was only one roundish crystal in the jar

Week 2: The solution was 1.5cm and the crystal was 2cm. The crystal hasn't grown in the last week, so I moved the jar to the windowsill . Small flecks of crystal are starting to grow at the bottom of the jar. The crystal is still the same shape.

Week 3: The solution was 1.3cm and the crystal was at 2cm. Because of the lack of growth, I moved the jar under my mum's work lamp. The jar has lots of smaller crystals lining the bottom. The solution has decreased by 2mm and the crystal is still the same size.

Final Crystal

My crystal wasn't very successful in the growth and nothing started to happen to the crystal until the second week. There might have been some problems with the crystal's growth because of the transport and the crystal getting nocked around a bit.

Activity: Word Search

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