Growing large, good quality crystals requires not only patience, care, and commitment, but also continual monitoring and assessment. The crystal growing project provides students with the opportunity to be actively involved in a long – term science project. The formation of a beautiful crystal at the conclusion of the project is extremely rewarding in itself. Additionally, the students learn much about crystals and their formation. Students are also required to write a short report on the project which further contributes to the learning process.
Making crystals is a business for many people. It is also the last step in production of many chemicals. The problem is that growing crystals is a slow process and we are trying to identify the conditions that can increase the rate of crystallization.
WHAT IS A CRYSTAL?
A crystal is a solid that consists of the various atoms, ions, or molecules being arranged in a uniform repeating pattern. This results in the material having a specific shape and color, and having other characteristic properties. Diamond (used in jewelry, and cutting tools) is an example of a crystal; it is made of pure carbon. Graphite (used in pencils and lubricants) is also a crystal made from carbon. Salt and sugar are also examples of crystals.
Recrystallization is a process that has been used to purify solid material by dissolving the solid (called a solute) in an appropriate liquid (called a solvent) and then having the material come out of solution in crystalline form. Depending upon conditions, one may obtain a mass of many small crystals or one large crystal.
More detailed information can be found on crystal types, shapes & sizes, light and color, how crystals form, and an encyclopedia review.
in terms of crystal systems and lattice types. There are 7 crystal systems:
PHYSICAL AND CHEMICAL PROPERTIES OF SUGAR
chemical names : sucrose, saccharose, beta-D-Fructofuranosyl-alpha-D-glucopyranoside
formula : C12H22O11
molar mass : 342.30
specific gravity : 1.587
melting point : 160 – 186 °C
crystal class : monoclinic spenoidal
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
If you just want to make crystals, you do not need a question, variables and a hypothesis; however you may want to study on a specific question about making sugar crystals. This is a sample question:
How does the temperature affect the speed of crystallization?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
If you just want to make crystals, you do not need a question, variables and a hypothesis; however you may want to study on a specific question about making sugar crystals. This is how you may define variables:
Independent variable (also known as manipulated variable) is the temperature.
Dependent variable (also known as responding variable) is the amount of crystals formed in a certain period of time.
Constants are the amount of water, the amount of sugar, the size of the jar in each crystallization trial.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
If you just want to make crystals, you do not need a question, variables and a hypothesis; however you may want to study on a specific question about making sugar crystals. This is a sample hypothesis:
Sugar solution forms crystals faster in cold temperatures.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Crystal Making Activity
Here is a procedure designed to produce many crystals using ordinary sugar.
HERE’S WHAT YOU DO
Pour the water into a saucepan and carefully heat it on the stove until the water boils, then turn off the heat.
Gradually add the sugar, a spoonful at a time, to the hot water and stir after each addition to dissolve. continue adding sugar gradually until no more will dissolve in the water. If necessary, heat the solution to make it clear.
Let the solution cool a bit and pour it into the tall jar. If the solution is too hot it might break the jar.
Cut a length of string which is about 6 mm (1/4 inch) shorter than the height of the jar. Attach a small weight (such as a piece of a clean rock) to one end of the string and tie the other end to the center of the pencil or narrow stick.
Let the solution cool (e.g. over night).
Moisten the string with water and rub some grains of sugar along the string. Let the string dry.
Slowly lower the string into the solution, making sure that the weight does not touch the bottom of the jar. Rest the pencil or stick across the rim.
Allow the solution and string to rest undisturbed for several days or weeks.
Watch what happens!
WHAT SHOULD HAPPEN?
You should see crystals growing in 5 to 15 days. If not, be patient; it might take longer.
The grains of sugar along the string act as ‘seeds’ on which crystals dissolved in the water are deposited as the sugar solution cools. The longer the string remains in the solution, the larger the crystals will grow.
After a while, the crystals will stop growing. To make them even bigger, carefully remove the crystals on the string. Pour the liquid into a sauce pan, carefully heat again, add more sugar, and repeat steps 2 and 3 above. Put your sugar string back into the solution.
All sugar crystals have the same characteristic shape regardless of size.
Please be patient. Remember, growing crystals takes time.
Experiment 1: How does the temperature affect the speed of crystallization?
1. Make a strong sugar solution (Boil 2 cups of water in a small sauce pan, add 4 cups of sugar, stir the mixture until the sugar is fully dissolved and you get a clear solution).
2. Transfer the solution to 3 identical plastic cups. Make sure all three cups have the same amount of sugar solution.
3. Cover all three cups with a plastic wrap
4. Place one of the cups in the refrigerator.
5. Keep one of the cups in room temperature.
6. Place the last cup in a warm place such as a warm oven (NOT HOT).
7. After one day, open all three cups. Empty the excess syrup and weigh the cups.
8. Which cup has the most crystal?
Your results table may look like this:
|Temperature||Mass of Grown Crystals|
|Room Temperature (72ºF)|
|Warm Place (110ºF)|
Make a graph:
Use the above table and make a bar graph for visual presentation of your results. Make one vertical bar for each of the temperatures you test. Write the condition or temperature under each bar (For example you may write refrigerator under one of the bars)
The height of each bar represents the mass of crystals formed in that temperature.
Seed crystals are very important in formation of sugar crystals. Seed crystals can be planted on the string or on a bamboo skewer, like sugar sticks.
To prepare a bamboo skewer with crystal seeds, first insect the stick in sugar solution so it becomes sticky.
Remove excess liquid by rubbing the skewer against the container. Then insert the skewer in a pile of sugar. Small sugar crystals will stick to the skewer. Let it dry in a warm place.
After your sugar solution cools off, insect the seeded bamboo skewer in the solution.
To hold the stick in place, you may use a piece of cardboard. Simply make a small hole in the center of a piece of cardboard and pass the skewer through the hole.
In a highly concentrated solution, you can see the growth of crystals as soon as you insert the seeded skewer in the solution. It will take about 7 days for crystals to become as large as commercially available sugar sticks.
Food coloring may be used to make sugar crystals in different colors.
Materials and Equipment:
HERE’s WHAT YOU NEED
- 1 cup water (distilled water works best)
- 1-1/2 to 2 cups granulated sugar
- 1 tall empty jar
- 1 Popsicle stick
- 1 paper clip
- fine string
- small saucepan
** You may already have a kitchen scale that can be used for your experiment. If you need need to buy one, make sure you buy a scale that measures in grams. Any scale with a capacity of 300 grams up to 500 grams will usually have the precision you need for your experiment.
Use this link to see samples of scales available at WWW.KLK.COM online store.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Keep track and record the amount of water and sugar that you use. Also record results in a time table.
Summery of Results:
Crystals need time to form and when they start growing, they appear everywhere, not just where we intend. As you have seen in the pictures, many crystals formed at the bottom and sides of the pan. We may find a nicely formed crystal among many others and use that as a seed for later experiments and get a larger crystal.
We hanged a string with a large knot at the bottom of that into the pan and expected the crystals grow on the knot. A small crystal ball formed on the knot, but many more crystals formed at the surface, sides and bottom of the pan. Picture in the left shows some of the side and surface crystals. Close observation
Making sugar crystals is a fine task and needs accuracy and attention. Overheating the solution can cause decomposition and great discoloration. Too much sugar in solution can cause over saturation. Not enough sugar will cause under-saturation and in all these cases there will be no crystals.
The updated recipe that is now an attachment at the bottom of this project is made after some experiments and fine tuning the procedures.
Picture in the right shows a small crystal ball formed after 3 weeks in a saturated sugar solution. This crystal is formed on a knot at the bottom of the string.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Updated Recipe 1:
Making Rock Candy
Crystal Growing Experiment – Making Rock Candy
This is a nice little experiment for young scientists.
600 grams (21 ounces) of sucrose (table sugar)
8 ounces of tap water
a pot, beaker or saucepan to heat and mix the solution
a candy thermometer (need to be able to measure 170°F)
a spoon for mixing the solution
heat source (stove)
crystal growing container (glass or plastic which can tolerate boiling water)
Caution! Since this experiment involves heat, hot containers, and a hot sugar solution, there is the risk of burns. Use extreme caution to protect yourself from burns. Children should be supervised by an adult when performing this experiment because of the risk of burns.
Place 600 grams (21 ounces) of sugar into the pot for mixing and heating.
Pour 8 ounces (one cup) of water into the pot containing the sugar.
Stir the sugar and water until all the sugar is wet but not dissolved.
Heat the solution, stirring constantly. Place the candy thermometer into the solution to measure the temperature of the solution. Stir constantly until the solution is 170°F then remove the solution from the heat.
Continue to stir the solution as the solution cools to 125°F.
Pour the 125°F (HOT!) solution into the crystal growing vessel. Remember to use a vessel which will tolerate boiling water!
Allow the solution to cool to room temperature. Close/seal the container.
Crystal will grow in the container within 2 to 3 days. Maximum crystal growth will occur by 7 days. One can grow more and larger crystals by allowing water to evaporate from the solution (Crystallization by evaporation). Punch or cut holes in the top of the container or simply leave the lid off the container. It may take many weeks for the water to evaporate, therefore this method of crystal growth is much slower.
Adding more sugar will result in more crystals (likely smaller) and a more rapid appearance of the crystals.
Updated Recipe 2:
There are two simple basic methods to grow crystals from a sugar solution
The Evaporation Method
The Slowly Cooling Method
Using the evaporation method you simply let water to evaporate of your saturated solution to get crystals. Its quite simple but may take a long time.
Using the slowly cooling method you produce a hot saturated solution and let cool it down slowly to get the crystals.
The catch is let it cool down slowly. As slower a solution cools down as bigger and finer the crystals will be. Fortunately the solubility of sugar rises greatly when the temperature goes up.
The good thing is this method is quick you will get nice sized crystals within several hours to days.
The Evaporation Method
Dissolve per 100 grams of water 230 grams of sugar heat up the solution until it boils and gets clear. The solution may have a slight yellow hue. For heating up the solution use a cooking pot or a vessel made from heat resistant glass (Pyrex), as for example replacement jars for electric coffee machines. You may also use the microwave but of course only use vessels which are suitable for this (no metal or metal parts in microwave!).
To grow the crystals you can use any kind of galas or plastic container with a wide open mouth. For example preservation glasses etc. You should produce at least about 500 ml of solution better around 1000 ml (or a quart).
After the covered solution has cooled down so after two or three days there should be some sugar crystals at the bottom of the jar. If not throw in some little grains of sugar. Let the solution stay alone and covered for about a week.
If you got no crystals on the bottom, yet even after throwing in some sugar grains your solution can not be saturated and won’t work.
This may happen either because you made a mistake with the amounts of water and sugar used or your room temperature is well above 20 °C (app. 70 °F).
To avoid mistakes in the amounts of water and sugar used, use an electronic kitchen scale which should have at least a resolution of 2 grams (better 1 gram) most can be switched from oz./lbs to metric, metric is easier to calculate. Also weigh the water as its much more accurate as measuring the volume.
Okay everything worked fine, there are some crystals at the bottom and the solution rested for a week. Now pour the solution in your final freshly cleaned growing vessel. You may filter but its not absolutely necessary and filtering the viscose solution may take for ever.
Now you need a seed crystal, usually you will find at the bottom nicely sized sugar crystals already suitable for this purpose or you may use a bought candy sugar crystal (that’s cheating !). Dry up the crystal with some paper towel and fix it with a slip knot to a thread of “invisible sewing thread” which is a thin clear thread of nylon or use very thin fishing line. Don’t use regular threads made out of cotton etc. as they work like a wick and are easily visible in the ready crystal.
Fix the thread to a piece of wood or a pencil for example so that the crystal suspends somehow above 2 – 3 cm (about one inch) the bottom of your growing vessel but well below the surface of the solution. Before doing that rinse the crystal on the thread shortly in cold water.
The growing vessel must stay open to allow the water to evaporate but you may cover it with a thin paper towel (most paper towels are multi layer so you may split them) to prevent flies, wasps, dust etc. from falling into the solution.
As the water evaporates your seed crystal will grow.
This will not work if you are in a very humid climate or if your room temperature changes and goes up.
As evaporation goes on there may grow additional crystals on the bottom of the vessel on the thread or on the sides. They grow on the cost of your desired main crystal. If so, pour the solution in a freshly cleaned other vessel rinse the crystal and the thread shortly in cold water (remove additional crystals which may have formed on the thread) and go on with evaporation.
The Slowly Cooling Method
If you produced the saturated solution for the evaporation method and found some crystals at the bottom you already used the slowly cooling method to produce crystals ! To get bigger and better ones you just have to add more sugar (larger “security gap”) and take care that the solution cools down very slowly.
A good basic recipe is to add 230 to 300 grams of sugar to 100 grams of water, heat up until the solution boils and gets clear. Pour the solution in your final growing vessel and close it tightly. Take care that the the solution cools down very slowly by insulating it and also avoid any moving, shaking or vibration of the solution.
You may give the crystals a better surface to grow, a matrix, if you put in a piece of rock, or have it suspended on a thread, or use a metal paper clip on a thread.
It takes a few hours to days, depending on how much solution you take and how good your insulation is, until the solution has cooled down to room temperature and the crystals are ready.
They main problems you may have with the slowly cooling method is that the solution does not cool down slowly enough, which results in small crystals or your solution has cooled down but there are no crystals at all !
What happened ? Supersaturation ! Your solution contains much more sugar as “allowed” since there have not formed any seed crystals spontaneously. If the solution is disturbed or you throw in some little sugar grains crystallization starts immediately.
Since the growing velocity of sugar crystals is small, solutions are often slightly supersaturated when they have cooled down and so the crystals still grow a little while even if the temperature does not change anymore. So allow the crystals some extra time.