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What Variables Affect Crystal Growth?

Almost every solid that occurs in nature is made up of crystals, though the crystals may vary greatly in shape, size, and color. Salt, for instance, looks like rough sand to the unaided eye. However, when looked at using a hand lens or a microscope, you can see that the salt is actually made up of small cube-shaped crystals. The crystals of salt and many other substances are very small, but others are large enough to be seen without a hand lens or a microscope. Also, many crystals are transparent, while others are colored. What do you think causes crystals to be so different from one another?

Activity A

Required Materials

  • Baby food jars, clear film canisters, or other containers
  • Water (some warm and some at room temperature)
  • Measuring spoon (1 tsp = 5 ml)
  • Copper sulfate, salt, sugar, borax, or other crystal-forming substance
  • Slides
  • Dropper or straw
  • Field microscope
  • Hand lens
  • Science notebook

Activity Directions

  1. With your group, create a list of the things necessary for crystals to form and write it down in your science notebook. Then, choose one or more things that you want to change (your variables) when you make a new batch of crystals.

  2. Design a way to test how each variable affects crystal growth and how you are going to record your data. Record your plan in your science notebook.

  3. Exchange science notebooks with another group. Can they understand which variable you are testing? Do they know what materials are needed? Are your instructions clear enough so that they could copy your experiment? Make any necessary changes to make your plan as straightforward as possible.

  4. List each variable that you wish to test and predict what you think will happen. When you are done with your experiment, you can look back and see how accurate your predictions were.

  5. Now conduct your experiment and let the crystals sit undisturbed for at least 24 hours.

  6. Record your results and draw the crystals in your science notebook.

  7. Share your results with the class and respond to the questions that follow in your science notebook.

      Did other groups choose the same variable?

      Were their results the same?

      What other questions do you have about crystal making?

Activity B

Variable 1: Temperature

Required Materials

  • 2 containers
  • Cup containing warm water and a cup containing cool water
  • Measuring spoon (1 tsp. = 5 ml)
  • 2 teaspoons of copper sulfate or other crystal-forming substance
  • 2 slides
  • Dropper or straw
  • Field microscope
  • Hand lens
  • Science notebook

Activity Directions

Day 1

  1. Mark one of your containers with an H and the other with a C.

  2. Put 10 ml (2 tsp.) of warm water in the container marked H.

  3. Put 10 ml (2 tsp.) of cool water in the container marked C.

  4. Add about 7 grams (1 tsp.) of copper sulfate or the chemical you are using to each container.

  5. Shake or stir each container until all of the chemical is dissolved.

  6. Label two microscope slides, one H and one C.

  7. Using a dropper or straw put 2 drops of liquid from container H onto slide H.

  8. Put 2 drops of liquid from container C onto slide C.

  9. Put the two slides where they will not be disturbed. You will observe them tomorrow.

  10. Answer the following questions in your science notebook:

      Based on the crystals you grew in Activity 14, what do you think your new crystals will look like?

      What do you think the results of your experiment will be?

      How do you think the temperature will affect the crystals?

Day 2

  1. First use your hand lens to observe both slides and record what you see in your science notebook. Then use your microscope and do the same thing. Record observations by writing and drawing what you see.

  2. In your science notebook write about the difference between the crystals grown using warm water and the crystals grown using cool water.

  3. Can you answer the question, Does the temperature of water in a solution affect crystal growth? Be prepared to share your results with the rest of the class.

Variable 2: Method of Mixing the Solution

Required Materials

  • 2 containers
  • Warm water
  • Measuring spoon (1 tsp. = 5 ml)
  • 2 teaspoons of copper sulfate or other crystal-forming substance
  • 2 slides
  • Dropper or straw
  • Field microscope
  • Hand lens
  • Science notebook

Activity Directions

Day 1

  1. Label one of your containers S and the other NS.

  2. Put 10 ml (2 tsp.) of warm water in the container marked S.

  3. Put 10 ml (2 tsp.) of warm water in the container marked NS.

  4. Add about 7 grams (1 tsp.) of copper sulfate or other crystal-forming chemical to each container.

  5. Shake or stir container S until all of the chemical is dissolved. Do not shake or stir the copper sulfate in the container marked NS. Simply allow this container to sit for about 5 minutes.

  6. Label 2 microscope slides, one S and the other NS.

  7. Using a dropper or straw put 2 drops of liquid from container S onto slide S.

  8. Put 2 drops of liquid from container NS onto slide NS.

  9. Put the two slides where they will not be disturbed. You will observe them tomorrow.

  10. Answer the following questions in your science notebook:

      Based on the crystals you grew in Activity 14, what do you think your new crystals will look like?

      What do you think the results of your experiment will be?

      How do you think the method of mixing the solution will affect the crystals?

Day 2

  1. First use your hand lens to observe both slides and record what you see in your science notebook. Then use your microscope and do the same thing. Record observations by writing and drawing what you see in your science notebook.

  2. In your science notebook write about the difference between crystals grown using a solution that was stirred or shaken and the crystals grown using a solution that was not stirred or shaken.

  3. Can you answer the question, Does the method of mixing the solution affect crystal growth? Be prepared to share your results with the rest of the class.

Variable 3: Amount of Chemical

Required Materials

  • 2 containers
  • Warm water
  • Measuring spoon (1 tsp. = 5 ml)
  • 1 1/2 teaspoons of copper sulfate or other crystal-forming substance
  • 2 slides
  • Dropper or straw
  • Field microscope
  • Hand lens
  • Science notebook

Activity Directions

Day 1

  1. Mark one of your containers with a 1/2, and the other with a 1.

  2. Put 10 ml (2 tsp.) of warm water in the container marked 1/2.

  3. Put 10 ml (2 tsp.) of warm water in the container marked 1.

  4. Add about 3.5 g (1/2 tsp.) of copper sulfate or other crystal-forming chemical to the container marked 1/2.

  5. Add approximately 7 g (1 tsp.) of the same chemical to the container marked 1.

  6. Shake or stir both containers until the chemical is dissolved.

  7. Label two microscope slides. One slide should be marked 1/2 and one slide should be marked 1.

  8. Using a dropper or straw put 2 drops of liquid from container 1/2 on to slide 1/2.

  9. Put two drops of liquid from container 1 on to slide 1.

  10. Put the two slides where they will not be disturbed. You will observe them tomorrow.

  11. Answer the following questions in your science notebook:

      Based on the crystals you grew in Activity 14, what do you think your new crystals will look like?

      What do you think the results of your experiment will be?

      How do you think the amount of chemical will affect the crystals?

Day 2

  1. First use your hand lens to observe both slides. Then use your microscope and do the same thing. Record your observations by writing and drawing what you see in your science notebook.

  2. In your science notebook write about the difference between crystals grown using different amounts of chemical.

  3. Can you answer the question, Does the amount of chemical affect crystal growth? Be prepared to share your results with the rest of the class.

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