Cibao Chua 2013
1. What is a crystal?
A crystal is a solid object which is made up of an ordered repeating pattern of the same atom or molecule.
2. What substances can be used to make crystals?
There are many different types of substances that can be used to make crystals including, potassium alum, borax, copper sulphate, Epsom salt and monoammonium phosphate. Each of these substances create a different crystal. For example Epsom salt crystals typically look like shards or spikes. The crystals start off clear,but they whiten over time. Monoammonium phosphate crystals look like emeralds and are shaped to look very rectangular.
3. What are some examples of crystals in nature? What household items can you also grow crystals from?
Some examples of crystals in nature include-snowflakes and diamonds.
Surprisingly, we have quite a few items found in our house that we can use to grow crystals. They include using- table salt (sodium chloride), distilled water and sugar (sucrose).
4. Explain the process of crystal growth.
Nucleation is the process in which crystals grow. This process takes place when the solute particles come together to form a nucleus, which will grow into a crystal. This means you will want a concentrated solution with as much solute as you can dissolve (saturated solution). Sometimes nucleation can occur simply through the interactions between the solute particles in the solution (called unassisted nucleation), but sometimes it's better to provided a sort of meeting place for solute particles to aggregate (assisted nucleation). For example you might tie a string around your crystal seed then tie it off onto a pencil to keep it suspended. It is best to choose a string with a rough surface compared to a smooth surface because that way, the nucleation process will happen more effectively.
5. Explain how crystals can grow in different shapes and sizes.
Crystals grow into certain shapes because the atoms or molecules join together in a pattern that repeats itself over and over to create a certain shape. A crystal grows by adding atoms or molecules to all its sides in the exact same pattern as the atoms and molecules that were added before. Because each different crystal is made up of a different building block (atom or molecule)they each have a different structure or shape. Some crystals grow into cubic or hexagonal shapes. Other crystals may grow into monoclinic, triclinic or rhombic shapes.
6. Outline a few different types of crystals.
A few types of different crystals include: Sugar, Salt, Diamond, Snow Bath salts and Quartz.
7. What effect do crystals have on light travelling through them? (relate to reflection, refraction, dispersion and diffraction)
Crystals often have high refractive index which means much of the light entering the crystal is totally internally reflected many times, causing the crystals to 'sparkle'. The cutting of facets at certain angles increases the amount of total internal reflection by reflecting the light at an angle greater than the crystals 'critical angle', causing it to sparkle even more.Crystals also cause dispersion and that is why sometimes you can see other colours (such as red and yellow) as the white light is broken. As you can see in this picture of a diamond ring below, there are small specs of colour. This is due to dispersion.
8. What are the optimum conditions for crystal growth?
Crystals grow when water evaporates from the solution. So while crystals can grow in the dark, it would take a much longer time. This is why it is recommended for crystals to grow somewhere warm, for example the windowsill or under a lamp. When the temperature is warm, the solution will evaporate more quickly. Crystal growth also requires light. Light evaporates water as heat does.
· 25g of potash alum
· 2 beakers
· 170 mL of hot water
· Stirring rod
· Filter funnel
· Filter paper
· Watch glass/filter paper
1. Make sure all apparatus is clean and dry.
2. Place approximately 25 g of potash alum in a beaker (250 ml or bigger) and add approximately 170 ml of hot water.
3. Stir the mixture until all the crystals have dissolved.
4. Filter the warm solution through a filter funnel (in which filter paper has been inserted) into another clean beaker.
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.
6. The first beaker and funnel can be washed and dried and the residue and filter paper used for filtration discarded.
· Plastic spoon/ spatula/ tongs /tweezers
· Loose fitting paper hat
1. (The next day) Observe the beaker of solution.
2. Carefully decant the clear solution above the crystals into a clean beaker and set it aside for later, leaving the crystals behind in the other beaker.
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.
4. 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.
5. Cover the solution with a loose-fitting paper hat that permits water to evaporate slowly whilst keeping out dust.
1. Evenly distribute the solution into each jar
2. Place your seeds carefully in your jar (choose the largest, or put a few)
3. Put a ruler next to your jar and take a picture to record the solution levels
4. Take your jar home and put it somewhere not in direct sunlight or near a heater. Also try to avoid disturbing your crystals as much as possible.
Day 1 and Day 2 Observations-
When we went to go see our beaker the day after, we noticed that there were no signs of crystals forming. My group concluded that it may have been due to using hot water from the tap, instead of boiled water in a kettle. The impurities in the tap water may have entered the solution and prevented any formation of the crystal. As a result of this, we had to complete the process all over again but this time we were careful in washing everything clean and using boiled water from the kettle. We were also much more patient in waiting for the solution to filter through. Instead of putting the beaker on the windowsill, like we did previously, we stored it in a cupboard where it was dry with no sudden temperature change. However, we didn't get any crystals from our new solution. We went back to check our old solution and noticed that crystals had started forming. They were still quite small and flat but there was quite a lot of them; around 10-14.
Day 3 Observations-
On this day, we transferred the crystals inside the beaker into our jars. We made sure the solution was equally poured into each jars. In the end, I had 3 crystal seeds in my jar and about 2.5cm of solution.
During the first two weeks of growing my crystal, the size and shape remained the same. It was still quite small around 0.3cm and very flat. Around the sides of the jar, small crystals grew and stuck together forming some sort of “rim”. There was around 1cm of water during the two weeks. The solution levels did not change so I decided it was time to change where I put my jar to give my crystals the best conditions to grow. I decided to put it on the windowsill, directly facing the sun(but not in the sun) , which would mean the solution would hopefully evaporate faster. This was extremely effective, because around 4 days after, I noticed big changes. My crystals had almost doubled in size from what it started off as and the solution levels had gone down to 0.5cm. The crystals all bonded together and so there was not one distinct crystal, rather clusters of small crystals.
Overall, my crystal took a very long time to grow bigger in size. It was only during the last 1 week or so where I noticed some differences and the crystals grew to about 0.7cm-1.2cm big. They turned out to be very flat and not as three dimensional as I had hoped them to be. The solution has still not finished evaporating yet and there is still around 0.5cm of liquid left. Since the crystals are clusters of smaller crystals bonded together, it is very fragile and can easily be separated from its "cluster". To conclude, my crystals have not grown very big, however there is one cluster where it appears more three-dimensional and is bonded much more strongly, compared to the other crystals.
My final images of my crystals display how crystals can grow into all shapes and sizes and that they are translucent so they allow more light through,which therefore makes the crystals appear more "shiny" and "bright".