Name: ______Period: ______Date: ______

Growing Crystals of Ionic Compounds GLO’s: ______HOM: ______

Background Information: The ions (charged atoms) that make up an ionic compound are bonded together in a repeating three-dimensional pattern called a crystal lattice. The simplest crystal lattice is the simple cubic structure, where the atoms lie on a grid: so that the positive ions are nearest to the negative ions. The shape of all crystal lattice structures depend on the pattern of ions in the crystal lattice. When you look at a pure crystal you are seeing how the atoms are arranged at the molecular level. Because this pattern keeps repeating itself it becomes large enough for you to “see” the arrangement of the atoms

Scientists grow crystals of various compounds so that they can see how the atoms are arranged. One method of growing crystals is called recrystallization. This is a process that is 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 a saturated solution in crystalline form. As the solvent evaporates the solid crystals begin to grow larger.

Minerals are the building blocks of rocks, which are the building of the Earth. They are, quite literally, all around us. We use them to build our homes, cars, and toys. Our bodies even produce minerals, such as the apatite that forms your teeth.

In nature, minerals can form from molten rock below the surface of the earth. Minerals can form as salts that precipitate out of water bodies, such as lakes. Some minerals even form from hot vapors. Today you can put on your mineralogist hat and grow some minerals of your own! Observe how they form, how they are shaped, and experiment with what conditions affect their growth.

Important things to know:  Supersaturated solutions and seed crystals o By heating the water and dissolving the borax, you are able to dissolve more borax than what is normally possible at room temperature. o As the solution cools, the solution is supersaturated until a seed crystal or other disturbance, such as your pipe cleaner, is added. o Crystals of sodium borate will start to form on the pipe cleaner. The pipe cleaner is a great surface for crystal formation because it has so much surface area on each little fiber.  Formation of crystal size o Sodium borate forms a particularly shaped crystal but the crystal can vary in size based on the speed at which the solution cools. o The faster the solution cools, the smaller the crystals because they don’t have as much time to organize themselves. o Slow-cooling solutions will tend to have larger crystals. This is similar to when igneous rocks (rocks from volcanic activity) form. Rocks on the earth’s surface cool quickly and will have small crystals, like obsidian, whereas rocks that cool within the earth tend to have larger crystals, like granite, because they take longer to cool.

Objective: Observe the arrangement of atoms of Borax (Sodium Borate – Na2B4O7) by identifying the crystal shape that grows after completion of the recrystallization process. Materials:  Beaker  Pipe Cleaner  String  Borax powder (sodium borate)  Water  Hotplate  Stirring Rod Procedure:

1. Bring a beaker of water to a boil. For a 250 mL beaker, add 4-5 heaping spoons full of borax and stir until dissolved. Adjust amount of Borax according to beaker size. 2. Shape the pipe cleaner into any desired form, such as a heart, star, or Christmas tree, taking care that it is small enough to not touch the sides of the beaker when immersed. 3. Attach your design to a popsicle stick with a string. 4. Dip the pipe cleaner in the solution and let it sit overnight, suspended from the rod and string. In the morning, the pipe cleaner will be transformed into a unique ornament that looks great on gift boxes or the tree.

Note: the pipecleaner should NOT directly touch the solution.

Result: Draw your borax crystals and Sodium chloride on the space below:

Borax crystals Sodium chloride crystals (Research this) Discussion: (Answer in complete sentences) 1. What shape are your borax crystals? ______2. Do the borax/Sodium chloride crystals grow separately, or do they often grow together? ______

3. What colors are your crystals? Are they shiny? Do the surfaces look flat or a little curved? ______4. Why did we use hot water to dissolve the borax and sodium chloride? Why did it precipitate out or form crystals, as it cooled down? Did it help that the water was evaporating? ______5. What would happen if you put your borax crystals/sodium chloride back into some hot water? ______6. What other shapes can you grow crystals on? ______7. What conditions affect how crystals grow? ______8. Are all crystals shaped the same? Do all crystals grow the same way? ______9. Do crystals grow on any surface like paperclips, nails, marbles, strings etc? Explain your answer. ______

Conclusion: ______

Reflection: 1. What did you learn from this lab? ______

2. What variable are you going to change in your next lab? ______

3. What questions do you have for this activity? ______