Growing Crystals Name _________________ Modified from Exploring Minerals and Crystals, Geoscience Australia. Education and Outreach Editor: Katy Tomkins Purpose: to create and examine crystals of soluble salts to determine their crystalline shape. SAFETY: Wear goggles, aprons, and closed toed shoes. DO NOT TASTE and materials.

Part 1: Sodium Chloride Crystals Chemicals:

• Sodium Chloride • Warm water

Equipment: • Plastic cup • Short piece of string • Hot plate with magnetic stirrer

• Beral pipet • Glass slide • Hand Lens

Procedure: Some producers of salt coat the grains with a harmless insoluble substance so that the grains will not stick together in damp weather. The following procedure is used to separate this coating and any un-dissolved salt from the solution.

Day 1: 1. Put about 6 grams of salt into 80 mL of water in a 250 mL beaker. 2. Place the beaker on a hot plate and turn the stirring bar on a low setting. Most of the salt will dissolve

forming a solution of salt in water, but some will remain in the bottom of the container and the solution may appear cloudy.

3. Let the mixture stand overnight. Next class, the solution will appear clear.

Day 2: 4. Label the glass slide “NaCl.” Use a Beral pipet to place a drop of the solution on the glass slide. 5. Pour the clear solution into a shallow glass or cup, being careful not to stir up any of the material from the

bottom. This process of separating a liquid from a solid, simply by pouring the liquid off is called decanting. 6. Discard the solid material. 7. Dip a piece of string into the salt water and let it hang over the side of the glass. This provides a place for

the crystals to grow. Let the clear solution stand, uncovered, for several days. 8. To keep the dust out you may want to cover the container.

Part 2: Sucrose Crystals Chemicals:

• Sugar • Water Equipment:

• Beaker (250 mL or so) • Paper clip • Popsicle stick • glass slide

• String • Plastic cups • Hot plate with magnetic stirrer • Beral pipet

Procedure, Day 1:

1. Place 150 mL of water in a 400 mL beaker. 2. Place the beaker on a hot plate set to about 5-6. Add a stirring bar and set the stirring rate to LOW. 3. Gradually add about 200 grams of sugar. Keep adding sugar until no more dissolves (thus creating a super

saturated solution) Only a few grains should remain undissolved. 4. Pour the solution into a plastic cup. 5. Tie some string onto a popsicle stick. Tie a paper clip on the other end. Hang the paper clip in the solution,

suspended from the stick across the top of the cup. 6. Label the glass slide “sucrose.” Use a Beral pipet to place a drop of solution on the glass slide. Set aside.

Part 3: Copper Sulfate Crystals Chemicals:

Approximately 3 grams copper sulfate • Water Equipment: • 50 mL Beaker • Beral pipet • Glass slide

Procedure, Day 1:

7. Place 20 mL of water in a 50 mL beaker. 8. Add about 3 grams of copper sulfate CuSO4 and stir occasionally until dissolved. 9. Label the beaker and set aside for later observation. 10. Label the glass slide “CuSO4.” Use a Beral pipet to place a drop of solution on the glass slide. Set it aside.

Magnesium Sulfate Dripper This activity demonstrates the formation of stalagmites and stalactites. Water containing dissolved Epsom salts moves through a piece of string. As the water evaporates, crystals of Epsom salts are deposited. The Epsom salt formations are models of how crystal deposits form in caves, but it should be noted that cave formations are made of calcium carbonate. Chemicals:

• Epsom salts (magnesium sulfate) • water

Equipment:

• 1 Liter Beaker • Two plastic cups • Thick string • Plastic wrap • Hot plate with magnetic stirrer • Scissors

• Washers • Plastic plates • Ruler • Paper • Food color (optional

Procedure, Day 1:

1. Bring 500 mL of water and 125 grams of Epsom salts to a boil and use the magnetic stirrer to stir gently until all the solid dissolves. If you want, you can add food coloring at this point.

2. Divide this solution into two plastic cups or beakers set 10 cm apart on a plastic plate. 3. Label the glass slide “MgSO4.” Use a Beral pipet to place a drop of solution on the glass slide. Set it aside. 4. Take a 30cm long piece of thick string and tie a small metal washer or nut to each end. 5. Dip the string into one of the cups to get it completely wet then suspend it between both cups with one end of

the string in each cup. 6. Adjust the spacing of the cups so that the bottom of

the loop of string is below the level of the solution in each cup.

7. Cover each glass with a piece of plastic wrap, being careful not to press down on the string. The plastic wrap prevents evaporation that could cause crystals to form within the glasses. Capillary action causes the solution to be drawn up the string and over the edge of the glass. Gravity pulls the solution down to the lowest point of the hanging loop and causes it to drip off. If the dripping is slow enough, each drop will leave behind a deposit of Epsom salt, forming a stalactite.

8. Move the cups closer or further apart so that the drip rate is one drop every five to ten minutes.

9. If you plan to grow a long stalactite, move the glasses closer together every four hours or so. As the liquid is drawn up out of the glasses, the level of the solution drops, slowing the drip rate. Keep adjusting the distance between the glasses so that the drip rate remains at the optimum growth rate for your particular setup.

Borax crystals Borax forms beautiful crystals very quickly. Borax is much more soluble in hot water than in cold water, however, this is not true of all substances. Salt has a similar solubility in cold water as it has in hot water. Chemicals:

• Borax • Hot water Equipment:

• 250 mL beaker • Plastic cup • Hot plate with magnetic stirrer • Pipe cleaner

• Pencil • Beral pipet • Glass slide

Procedure:

1. Add about 20 grams of borax to 120 mL of water on the hot plate, stirring the mixture until the borax has dissolved completely.

2. Bend a pipe cleaner around a pencil so you can balance the pencil on top of the jar and have a short piece of pipe cleaner sticking down into the solution.

3. Label the glass slide “Borax.” Use a Beral pipet to place a drop of solution on the glass slide. Set it aside.

Borax crystal. Source: Geoscience Australia, photo credit: Katy Tomkins. At the end of class, place all your group’s materials on a sheet of paper and label with your class period and initials.

Growing Crystal Lab Conclusion: What crystal shape did you identify for each substance? Cite your evidence. What prevents the crystals from growing larger? How could you grow bigger, more perfectly shaped crystals?