Growing crystals- factors that affect the rate and the size

Introduction: (Initial Observation)

At first glance, crystals are beautiful.
When you learn more about the physical properties of crystals, their geometrical shapes, and the way they can be cut, they become more interesting.

When you learn about their scientific and industrial applications, they become valuable.

When you learn how much of the world economy depends on crystals, they become priceless.

Growing crystals is the first step in producing today’s semiconductors. Semiconductors are the heart of every computer processor, memory and other ICs. (Integrated Circuits).

Growing crystals is an art, a technology and a hobby. Every year there are many crystal growing contests around the country and around the world. The goal is making the largest crystal.

This project is an opportunity to explore the amazing world of crystals and perform some experiments on making crystals.

Information Gathering:

Find out about growing crystals. Read books, magazines or ask professionals who might know in order to learn about factors affecting crystal growth. Keep track of where you got your information from.
The Internet is a good source of information about crystals. Start by searching the net with keyword “Growing Crystals”. This gives you some links with basics of growing crystals such as:

http://www.beloit.edu/sepm/Rocks_and_minerals/growing_crystals.html

http://web.mit.edu/x-ray/cystallize.html

To find more details, be more specific and search for keywords like “growing a large crystal” or “growing the largest crystal”. This gives you some links with basics of growing crystals such as:

http://serc.carleton.edu/sp/mnstep/activities/34720.html

http://sciences.aum.edu/phs/crys1.html

http://xray.tamu.edu/pdf/notes/guidetocrystalgrowth.pdf

What is a saturated solution? How can I make it?

A saturated solution of any substance, is the solution that can not dissolve any more of that substance. For example a saturated solution of salt, is a saltwater solution that cannot take any more salt. In other words if you add more salts, it will remain at the bottom and does not dissolve.

To make a saturated solution of salt, you may start adding salt to water and stir it continuously until it dissolves. Continue adding salt and stirring until the solution does not dissolve any more salt and extra salt remains at the bottom of the container. This solution will be the saturated solution. You can transfer the saturated solution to a different container and ignore the extra salt.

How do I measure certain amounts of water or solution?

To measure liquids you may use a measuring cylinder also known as graduated cylinder. In a measuring cylinder, at least one side is marked with water level lines and numbers that show how many milliliters is the capacity bellow each line. For example the lines in a 500-ml measuring cylinder may be numbered 100ml, 200ml, 300ml, 400ml and 500ml. To measure 200ml, fill up the cylinder up to the 200ml line. That will make 200 ml of the liquid. Then you can transfer this liquid to another container for your

Question/ Purpose:

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.

The purpose of this project is to experiment growing crystals and find out what factors affect the rate of growth (Speed of growth) and the size of grown crystals. Some of the factors that you may choose to study are the subject of the following specific questions:

1. How does the initial concentration of a solution affect the rate of crystal growth? (Main question)
2. How does the initial concentration of a solution affect the size of crystals?
3. How does the cooling rate affect the rate of crystallization?
4. How does the cooling rate affect the size of crystals?

Hypothesis:

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.

This is a sample hypothesis for question number 1:

The rate of crystal growth increases by any increase in the initial concentration of solution.

Experiment Design:

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.”

Warning: This experiment requires adult help and supervision. It deals with very hot liquids.

Related Notes:

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.

 

 

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Additional Experiments:

Experiment 2:

In this experiment, we are going to investigate the factors which determine how big the crystals will grow. We will make a saturated solution of copper sulfate and aluminum potassium sulfate. Remember that a solution is created when a solute (in this case the two chemicals listed) is dissolved in a solvent (in this case, water). A saturated solution is created when so much solute is put into the solvent that no more can be dissolved. One way of thinking about it is that all the “holes” between the water molecules have been filled.

Method:

Obtain and prepare material:

• prepare 5 grams of copper sulfate (which is blue) and 5 grams of aluminum potassium sulfate (which is white).

 

• Make the saturated solution:

  • Set up a water bath over a hotplate using 2 beakers, one set inside the other.

  • In a small beaker, put 20 ml of water.

  • Heat the water in the water bath until it boils.
    

  • Slowly stir in a little of the mix of the 2 powders. When the powder has dissolved, pour in some more and mix until that, too has dissolved.

  • Continue pouring the powder in little by little until it has all dissolved.

• Pour a small quantity of the solution on a flat, wide dish so that it can cool quickly. Pour it out of the small beaker using the metal tweezers.

4.Leave the rest of the solution in the small beaker so that it can cool slowly.

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1. What was the point of this experiment? Remember that the point is the objective of the experiment, it is what we are trying to learn from it.
2. Draw diagrams of the two sets of crystals you obtained after one week. Clearly mark which ones formed in the beaker and which ones formed in the wide, flat dish (the Petri dish). Draw them to scale so that it is clear to see any differences in size.
3. Which crystals formed more quickly, the ones in the Petri dish or the ones in the beaker. Justify your answer. Use words such as “cooling” or “crystallizing”.
4. Based on the aim of the experiment and based on your observations of the results, write a conclusion for this experiment. Remember that in a conclusion we are addressing the question, “What did we learn from this?”

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Experiment 3:

In this experiment we test the effect of concentration on the rate of crystallization. Prepare 300 ml of a saturated solution of copper sulfate or aluminum potassium sulfate. Before leaving it for crystallization, transfer it to 3 identical cups or beakers so that each will have 100 ml of the solution.

Do not add anything to the first cup. Dilute the second cup by adding 20 ml of water. Dilute the third cup by adding 50 ml of water. Leave all three samples for crystallization and inspect them every day.

After how long did the saturated solution crystallize?

After how long did the second solution (20 ml water added) crystallize?

After how long did the third solution (50 ml water added) crystallize?

Enter your results in a table like this:

Experiment 4: How does the cooling rate affect the rate of crystallization?

Introduction: The cooling rate or the speed of cooling depends on the factors such as the environment temperature, size of container, heat exchange and air flow. For example the solution will cool off faster in a colder room and in a smaller container and in a metal container. (Metals are better heat conductors than glasses and plastics). In order to change the cooling rate in this experiment we will change the rate of heat exchange by adding insulating materials outside the crystallization containers.

Procedure:

1. Prepare 5 identical jars to be used as crystallization containers.
2. Number the jars from 1 to 5
3. Prepare some towels, paper bags, paper towels to be used as insulating materials.
4. Tie the 15 cm piece of string to the middle of the pencil.
5. Tie the paper clip (or bead) onto the end of the string.
6. Put the pencil across the top of a jar so that the string hangs down the middle of the container. If it hangs down too far, roll the string around the pencil until the string is not touching the sides or bottom of the jar. The string will act as a seed for the crystal (You may also want to insert the string in a can of sugar. Small sugar crystals attached to the string will help formation of new crystals). Any type of jar will do, but canning jars, pint size are especially nice, they will endure the hot temperatures. Tall skinny olive jars are also good because they don’t use up so much of the liquid.
7. Now that the string and pencil are ready remove them from the jar and put them aside
8. Get a helpful adult!
9. Pour five cups of water into a pot and bring it to boil. Then stop the heat.
10. Pour about one cup of sugar into the hot water, stirring until it dissolves.
11. Keep adding more and more sugar, each time stirring it until it dissolves, until no more will dissolve. This will take time and patience and it will take longer for the sugar to dissolve each time. Be sure you don’t give up too soon.
12. Have your friendly ADULT carefully pour the hot sugar solution into the jars to the top. Then submerge the paper clip and string into the sugar solution. Be sure the string hangs down in the middle of the jar.
13. Wrap the jar number 2 with one layer of insulating materials. Wrap the jar number 3 with 2 layers or thicker insulating materials. Use more insulating materials for jar number 4 and finally the jar number 5 will have the most insulating materials.
14. Allow the jars to cool and put it someplace where it will not be disturbed.
15. After 36 hours, open and inspect all the jars. Weigh each jar and then empty the excess water solution and then weight it again. In this way you will know how much of each solution remained and how much of that crystallized.

Your results table may look like this:

Cooling rate	Rate of crystallization	The size of the largest crystal
Very High (no insulation)
High (One layer of insulation)
Medium (2 layers of insulation)
Low (3 layers of insulation)
Very slow (most insulation)

Rate of crystallization is the weight of final crystals divided by the total weight of the mixture or solution.

Materials and Equipment:

Can be extracted from the experiment section.

What type of scale should I use?

MiniScience digital scales or any other gram scale (electronic or mechanical) will work.

You can purchase Copper Sulfate and Potassium Aluminum Sulfate from a local scientific supplier or from online stores such as MiniScience.com, klk.com and

Results of the Experiment (Observation):

The most important difference between the two containers is that the small dish has small crystals and the beaker has larger crystals. Other differences can be seen such as the intensity of the colors or the number of crystals formed.

Here are some photos of the copper sulfate crystal experiment.

Results:

One week later, here are the results:

 

 

 

 

 

 

 

 

 

Calculations:

If you do any calculations, write your calculations in this part of your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during the experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

The longer the time of formation, the bigger the crystals.

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.

Possible Errors:

There are many sources of error: the solution could have been over-saturated or under-saturated, the water could have gotten too hot and prevented the crystals from forming correctly, the solution could have been agitated while it was forming crystals, etc.

Possible remedies are: giving a specific mass of each powder and measuring the volume of the water in a graduated cylinder, putting a thermometer in the small beaker to make sure it does not get too hot, pouring out the liquid to cool in the place where the beakers will be stored to eliminate any unnecessary movement.

References:

List of References:

http://www.crystalgrowing.com

http://library.thinkquest.org/J002289/crystals.html

http://www.xray.ncsu.edu/GrowXtal.html