- Many solids are made of pieces with many small, flat sides. Such pieces are called crystals. Salt and sugar grains are examples of crystals. In this investigation, you will grow crystals in a solution.
MATERIALS NEEDED:
Safety goggles
Two 250-mL beakers
Wire screen
Hot plate
Hot pads
50 g alum, powder
500-mL jar with cover
*Small alum crystal
10-cm thread
Masking tape- *You need a small "seed" crystal. This can be made by dissolving alum in a small amount of hot water, much like method 2 in this lab, and letting the water evaporate.
PROCEDURE:
Method 1
WEAR SAFETY GOGGLES
Put 200 mL of water in a 250-mL beaker. Use a hotplate, covered with a wire screen, to heat the water to boiling. REMEMBER: Steam can burn you. Keep a safe distance from steam and boiling water.
Dissolve as much alum in the heated water as possible. If you spill any of the alum solution on your skin, wash with soap and water. If you get any in your eyes, flush them with plenty of water.
Using hot pads, transfer the solution to a 500-mL jar that has a cover. (A jar used for canning fruit works well.)
Allow the solution to cool. Then tie a small crystal of alum to the end of a thread about 10 cm long. Tape the other end of the thread to the inside of the jar cover. Lower the crystal into the solution and rest the cover loosely on the jar to allow water to evaporate and to keep dirt out. The crystal should hang near the center of the solution. If you want the evaporation to go quicker, you can hang the string from a rod across the jar mouth.Carefully set the jar in a place where it will not be disturbed. Check the sample each day for signs that the crystal is growing larger. Be sure not to disturb it.Method 2
WEAR SAFETY GOGGLES
Prepare another alum solution. This time dissolve as much alum as you can in 50 mL of hot water in a beaker. Using a hotplate, slowly heat the solution to remove most of the water. BE CAREFUL not to let it boil hard, or it could splatter hot solution. When the water is almost gone, use hot pads to remove the beaker from the hot plate. Watch for crystals to form as the alum solution cools. Save these crystals in a safe place so they can be compared with the crystals that form in the first solution.OBSERVATIONS:
Compare the sizes of the crystals formed in the two solutions.
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Do the alum crystals have the same shape?
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Describe the shape of an alum crystal.
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How can you produce the largest alum crystal?
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FURTHER INVESTIGATION:
- Try to grow other crystals. Follow the procedures in the first part of this lab, using copper sulfate instead of alum. Compare the crystal shapes of copper sulfate and alum. Try growing crystals from salt and sugar.
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- *You need a small "seed" crystal. This can be made by dissolving alum in a small amount of hot water, much like method 2 in this lab, and letting the water evaporate.
GROWING CRYSTALS
INTRODUCTION: