Variables For Making Rock Candy

A Science Fair Project is a cause/effect investigation.

The cause is called an independent variable (something you purposely change).

Changes in the independent variable effects another variable called the dependent variable.

You AFFECT the investigation by making changes in the independent variable. This change EFFECTS the dependent variable causing it to change.

Exploratory Experiment Rock Candy

Purpose: To grow a large number of sugar crystals on a string.

Identifying Variables

1. Dependent variable: This is generally identified by the purpose of the exploratory experiment.For example:

Purpose: To grow a large number of sugar crystals on a string.

Dependent variable: amount of sugar crystals

2. Independent variable: You now want to identify all the possible variables that might affect the development of sugar crystals. Do this by identify each variable in each procedure step of the exploratory experiment.

Exploratory Experiment Procedure + Independent Variables

Rock Candy: Growing Sugar Crystals

Notice: Whether you plan to eat the rock candy or not, use very clean materials so that you do not introduce variables (dirt–etc) that might affect the results.


1. Place 3 cups of sugar and 1 cup of tap water in a cooking pot.

a. quantity of sugar

b. quantity of water

2. Heat the mixture to boiling, stirring constantly. As soon as the mixture boils, all of the sugar should have dissolved and the solution is clear with a straw color. Remove the pot from the heat.

a. heating the mixture

b. amount of heating time (boil for a time period)

3. Add 10 drops of red food coloring. Stir the solution so that it is thoroughly colored.

a. quantity of food coloring

b. color of food coloring

4. Cover the pot with a paper towel and allow the pot to sit at room temperature for 10 minutes.

a. cover the pot –use different material

b. don’t cover the pot

c. cool the pot for a longer time

5. While the sugar solution is cooling, prepare the cotton string and jar. Use a slender jar, such as an olive jar that has a diameter of ————and a height of —————–.

Cut a —inch long cotton string .

a. length of string

b. type of string

Tie a Lifesaver candy to one end of the string. The candy serves as a weight to keep the string vertical.

a. type of weight

b. no weight

Drop the candy-end of the string into the jar. The string is to be vertical in the jar.

a. position of the string–slanted ? horizontal?

Raise the string so that the candy is suspended about —inches from the bottom of the jar.

a. height of string in the jar

b. string touches the bottom of the jar

Tie the free end of the string to a pencil and place the pencil across the mouth of the jar. Note: You want the string to be suspended vertically in the center of the jar with the candy end abou —-inches from the bottom of the jar.

a. how string is suspended in the jar

Seed the string by dipping the string into the sugar solution, and then sprinkle dry table sugar along the sticky string.

a. don’t dip in sugar solution –wet with water or other liquid

b. wet with sugar solution but don’t sprinkle with dry sugar

Hang the seeded string vertically in the jar, and then cover the jar with a paper towel while the sugar solution continues to cool.

a. how string is hung–at an angle? horizontally?

b. what the jar is covered with

c. don’t cover the jar

6. Place the paper covered pot containing the sugar solution in the refrigerator for 10 minutes. You want the liquid to be cooler than room temperature.

a. longer cooling time in the refrigerator

b. don’t cool in the refrigerator

c. don’t cover the pot

d. cover pot with a different material

7. After the solution has cooled in the refrigerator, raise the seeded string from the jar, pour the solution into the jar, and then lower the string so that it hangs in the center of the jar.

a. don’t raise the seeded string

8. Cover the jar with a paper towel and set it in a place where it will not be disturbed but can be observed. Note: You do not want the jar moved or vibrated.

a. cover the jar with a different material

b. don’t cover the jar

c. place jar where it will be disturbed–vibrated

9. Observe the growth of the sugar crystals for 7 days.

a. observe for a different amount of time–shorter–longer

Trouble shooting

1. Crystals grow on the surface of the solution.

Remove the crystals with as little disturbance to the string as possible.

2. Crystals grow on the inside and bottom of the jar.

Remove the string and hang it in clean jar.

Pour the crystallized solution into the cooking pot and bring it to a boil. Cool as before. Pour the cooled sugar solution into the clean jar. Add the string as before.