Growing Rock Candy: Variables

Experiment for Growing Sugar Crystals

Variables

Dependent Variable: amount of sugar crystals collected

Independent Variable:

The independent variable is a part of the experiment that if changed could affect the dependent variable.
I have identified all the possible independent variables in the following descriptive experiment. Notice that instead of just making a list of the variables, I have written a question comparing the independent variable and the dependent variable previously selected. The independent variable is in purple type and the dependent variable is bold faced.

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

a. What effect would changing the quantity of sugar have on the amount of sugar crystals collected?

b. What effect would changing the quantity of water have on the amount of sugar crystals collected?

c. What effect would changing the type of water have on the amount of sugar crystals collected?

Step 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. What effect would changing the quantity of heat have on the amount of sugar crystals collected?

b. What effect would changing the length of boiling have on the amount of sugar crystals collected?

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

a. What effect would changing the quantity of food coloring have on the amount of sugar crystals collected?

b. What effect would changing the color of food coloring have on the amount of sugar crystals collected?

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

a. What effect would changing the type of covering have on the amount of sugar crystals collected?

b. What effect would changing the how much of the pot is covered have on the amount of sugar crystals collected?

c. What effect would changing the cooling time of the sugar solution have on the amount of sugar crystals collected?

Step 5. Prepare the growing jar. Thoroughly clean a see-through slender glass jar that is at least six inches tall with a diameter of at least 3 inches.

a. What effect would changing the size of the jar have on the amount of sugar crystals collected?

Step 6. Prepare the growing string.

(1.) Cut a cotton string at least 3 inches longer than the height of the growing jar.

a. What effect would changing the length of the string have on the amount of sugar crystals collected?

b. What effect would changing the type of string have on the amount of sugar crystals collected?

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

a. What effect would changing the type of weight have on the amount of sugar crystals collected?

b. What effect would changing the amount of weight have on the amount of sugar crystals collected?

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

a. What effect would changing the the angle of the string in the jar have on the amount of sugar crystals collected?

(4.) Raise the string so that the candy is suspended 2 inches from the bottom of the jar. Tie the free end of the string to a pencil and place the pencil across the mouth of the growing jar. Note: You want the string to be suspended vertically in the center of the jar with the candy end about 2 inches from the bottom of the jar.

a. What effect would changing the height of the string in the jar have on the amount of sugar crystals collected?

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

a. What effect would changing the wetting of the string have on the amount of sugar crystals collected?

b. What effect would changing the amount of sugar crystals added to the string have on the amount of sugar crystals collected?

(6) 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. What effect would changing the angle of the string in the jar have on the amount of sugar crystals collected?

b. What effect would changing the covering material for the jar have on the amount of sugar crystals collected?

a. What effect would changing the amount the jar opening is covered have on the amount of sugar crystals collected?

Step 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. What effect would changing the cooling time of the sugar solution have on the amount of sugar crystals collected?

b. What effect would changing the temperature of the cooled sugar solution have on the amount of sugar crystals collected?

c. What effect would changing the covering for the pot have on the amount of sugar crystals collected?

e. What effect would changing the amount the pot is covered have on the amount of sugar crystals collected?

Step 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. What effect would changing how the sugar solution is poured into the jar have on the amount of sugar crystals collected?

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

a. What effect would changing the material of the jar covering have on the amount of sugar crystals collected?

b. What effect would changing the amount of the jar opening that is covered have on the amount of sugar crystals collected?

c. What effect would changing the temperature of where the jar is placed have on the amount of sugar crystals collected?

a. What effect would vibrations of the growing jar have on the amount of sugar crystals collected?

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

a. What effect would changing the length of the observation time have on the amount of sugar crystals collected?

EXPERIMENT QUESTION

Once you have reviewed all the possible independent variables in the dependent experiment, chose one that you think will most affect the dependent variable. Or, choose a question that you are most interested in.

Example (6a)

What effect would changing the angle of the string in the jar have on the amount of sugar crystals collected?

EXPERIMENT HYPOTHESIS

So, what do you think? Will changing the angle of the string make any difference in the amount of sugar crystals collected? Also, if you change the string angle, you will also have to change other variables, such as the container as well as the depth of the sugar solution.

Fact: Gravity is a force that pulls everything toward the earth’s surface.

Example Hypothesis

Because gravity pulls things down, more sugar molecules would grow on the string if the string were horizontal. There would be more surface catching the falling sugar molecules.

EXPERIMENT PROCEDURE

The objective of the experiment is to determine if your hypothesis is correct under the conditions it will be performed. The experiment procedure steps will be those of the descriptive experiment except for the step involving the independent variable.

The independent variable is the position of the growing string. It needs to be horizontal instead of vertical. This change requires a different type of growing tray so the string can be stretched horizontally across the tray.

EXPERIMENT CONTROL

A control is generally the original descriptive experiment. But, since the experiment hypothesis question requires

This is the same experiment, but with the string in the original vertical position. Since there has to be a change in the container holding the sugar solution, you would have to use the same type of tray for the control. The objective for the control is to have something to compare your experimental results with.