EXPERIMENT TO DETERMINE WHAT ENVIRONMENTAL FACTORS ARE MOST

IMPORTANT TO GROW ROCK CANDY

Abby

Cary Academy

ABSTRACT

The purpose of this experiment was to determine what environmental factors caused

rock candy to grow. Sugar- water solutions were placed into different environments to

determine in which conditions it grew crystals/rock candy best. It was determined that

rock candy grew best under a heated lamp. The results are due to the fact that energy

was created by the heat, and that energy allowed the sugar molecules to bond faster in

a supersaturated solution that did not have a balance between the sugar and water and

that was trying to achieve equilibrium.

INTRODUCTION

Rock candy is one of the oldest and most pure forms of candy. In this experiment, the

growth rate of rock candy was tested in different environmental conditions to determine

which environmental condition was most important to grow rock candy. The experiment

attempted to grow rock candy in three types of environments.

To make or grow rock candy a lot of sugar is needed. Sugar is made up of three

elements: carbon, hydrogen, and oxygen. Sugar is made in nature by photosynthesis.

Photosynthesis occurs when sunlight is turned into energy by the chlorophyll in green

plants. Plant sugar is made when energy reacts with water and carbon dioxide. To

make one molecule of sugar, 12 atoms of carbon, 22 atoms of hydrogen, and 11 atoms

of oxygen are needed. Figure 1 shows the make-up of one molecule of sugar.

Figure 1: Atomic model of one molecule of sugar.

All green plants produce sugar in their leaves. Farmers grow sugar cane and sugar

beets for sugar. Great quantities of sugar are produced from those plants. Rock candy

is made from the sugar produced by these plants. Rock candy is made from a sugar

and water solution that is put into the correct growing environment. A solution is a

mixture of two or more substances that includes a solute and a solvent. To grow rock

candy, crystallization must occur. Crystallization occurs when a liquid solution changes

to a solid. For a solution to change from a liquid to a solid, it must become

supersaturated. Saturated means that the water in the solution has dissolved all the

sugar it possibly can at a given temperature. Any additional solute will not dissolve if

added to a saturated solution. To have a saturated solution, there must be more solute

than solvent in a solution. A solution can also become supersaturated. A

supersaturated solution is when a solution holds more of the dissolving material than

could be dissolved by the solvent under normal circumstances. Cooling the

temperature of a solution is one way to make it become supersaturated. A

supersaturated sugar solution has more sugar in it than can stay in a liquid form. It is at

this point that the supersaturated solution crystallizes and the liquid starts to become a

solid. In a sugar solution, this is when the crystals begin to grow. Crystals will continue

to grow as long as the sugar solution is not in equilibrium. Heat added to a solution will

create energy which will allow crystals to grow even faster because the molecules are

moving and attaching. Equilibrium will occur when the water can hold all the sugar in

liquid form and growth of the crystals will stop. A crystal is any solid material whose

atoms are arranged in a definite geometric pattern. It takes millions of unit cell

(individual structural units of atoms) to form a crystal. The cells repeat themselves in all

directions making crystal faces. Crystal faces are geometric shapes with flat surfaces.

Sugar is an isometric, cubic crystal which means that is has flat planes that are set at

fixed angles to one another. For crystals to grow larger, they must have perfect existing

conditions and outside forces.

Since all solutions used in the experiment were created in the same way and started at

the same saturation level, it was predicted that the sucrose growing under the light at

75 o F would grow the best because of the warm environment and the purity of the

sucrose. The warm environment will allow faster crystal growth because increase

energy in the molecules will cause the solution to reach equilibrium the fastest.

Figure 2: Process of crystallization.

MATERIALS AND METHOD

In this experiment a measuring cup, hot plate, cooking pan, stirrer, blue food coloring, a

lamp, glass containers, seeded sugar sticks, tape, pencils, table and pure sucrose

sugar, scale, cup, water, graduated cylinder and temperature probe were used.

The main experiment conducted was to determine the growth of crystals in different

environments/conditions. To begin the experiment, sugar-water solutions needed to be

made. To make a sugar-water solution, ¾ cups of water from the measuring cups was

added to the cooking pan. This cooking pan was then placed on the hotplate and the

water was brought to a boil. To bring the water to a boil, the hotplate was set on 10.

Once the water was boiling, 2 cups of table sugar were added to the boiling water. The

sugar and water were mixed until the bottom of the pan was visible and the sugar was

completely dissolved. The sugar-water solution was then complete. To begin the

experiment, the sugar- water solution was poured into a glass container. Then a

seeded sugar stick was stuck into the solution. The seeded sugar stick was necessary

for the crystals to grow on. However, to make sure the solution would hold the seeded

stick, a pencil was taped across the opening of the container and the stick rested on the

pencil to make sure that it would not move within the container. Overall, 5 sugar-water

solution containers were made. 4 of the 5 sugar-water solutions were made with table

sugar. The remaining sugar-water solution was made from pure sucrose sugar. The 5

containers were then placed in different temperature. 3 of the containers including the

container with pure sucrose-water solution were placed underneath a lamp that created

temperatures between 75-80 o F. 1 container was placed at room temperature and the

other container was put into the refrigerator. 7 drops of blue food coloring were added

to one of the table sugar-water solutions being grown under the heat lamp. The

containers were observed every school day to see if crystals had developed. If crystals

did exist, measurements were then taken by removing the sugar seeded stick with the

crystals and placing it on the scale. The crystals weight measured in grams was then

recorded.

As an additional experiment, a sugar-water mixture was created as explained above

except with different temperatures of water. This experiment was performed to see how

much sugar could be added at different temperatures until it became supersaturated.

Supersaturated means that the solution has more solvent (in this experiment sugar)

than it can dissolve. Three different temperatures of water were used in this

experiment. These different temperatures were cold water of 4.7 o C, boiling water

boiled on a hotplate until it reached 45.1 o C, and room temperature water of 23.2 o C.

The temperature of the water was determined for each by using the temperature probe.

To each of these different water temperatures, 25 mL of sugar as measured in the

graduated cylinder was added in intervals until the sugar was no longer being dissolved.

The amount of sugar used until the solution became supersaturated was recorded.

RESULTS

In the experiment to see if the sugar-water solution grew crystals/rock candy larger at

room temperature than under a heated lamp, it was determined that crystals/rock candy

grew the largest under the heated lamp because the final weight of the crystals/rock

candy grown under the heated lamp (41 g) was more than the grams of the crystals

grown at room temperature (24.6 g) as seen in Figure 3.

Figure 3: Growth of crystals under a heated lamp versus room temperature.

In the experiment to see if the sugar-water solution grew crystals/rock candy larger in a

refrigerator than under a heated lamp, it was determined that crystals/rock candy grew

larger under the heated lamp because the final weight of the crystals/rock candy grown

under the heated lamp (41 g) was more than the grams of the crystals/rock candy

grown in the refrigerator (8.5 g) as seen in Figure 4.

Figure 4:Growth of crystals in refrigerator versus under a heated lamp.

In the experiment to see if the sugar-water solution made from table sugar grew

crystals/rock candy larger under a heated lamp than the sugar-water solution made

from pure sucrose, it was determined that crystals/rock candy grew somewhat larger

under the heated lamp when the solution was made with pure sucrose (42 g) than when

the solution was made with table sugar (41 g) as seen in Figure 5.

Figure 5: Growth of crystals from sugar-water solution made with pure sucrose versus

table sugar.

In the experiment to see if the sugar-water solution grew crystals/rock candy larger with

blue dye than without blue dye, it was determined that crystals/rock candy grew larger

without blue dye (41 g) than with blue dye (15.1 g) added to the solution as seen in

Figure 6.

Figure 6: Growth of crystals using a sugar-water solution with blue dye and without blue

dye.

In this experiment to see which temperature of water dissolved the most sugar before it

became supersatured, it was determined that the heated water at 45.1oC dissolved the

most sugar (275 mL) and the cold water of 4.7o C dissolved the least amount of sugar

(205 mL) as seen in Figure 7.

Figure 7: Amount of sugar dissolved at different temperatures of water.

DISCUSSION

In this experiment, the sucrose- water solution grown under the heated lamp produced

crystals or rock candy that was larger and grew faster than any of the other sugar-water

solutions. The smallest growth of crystal or rock candy was when the sugar- water

solution was placed in the refrigerator. The weight of the crystals/rock candy in the

refrigerator at day 8 was 8.5 g, whereas the weight of the crystals/rock candy grown

under the heated lamp at day 6 was 22.8 g. The room temperature crystals/rock candy

consistently grew, but at a slower rate than under the heated lamp. At day 17, the

weight of the crystals/rock candy under the heated lamp was 33.5 g, whereas the

weight of the crystals/rock candy grown at room temperature was 24.6 g. It should be

noted that the table sugar-water solution grown under the heated lamp produced

crystals/rock candy that almost achieved the same size of the sucrose- water solution

but it took a longer time as shown in Figure 5. It took 15 days for the sucrose- water

solution to produce crystals/rock candy of 42 g whereas it took 20 days for the table

sugar-water solution to produce crystals/rock candy of 41 g. Most likely the sucrose

created more rapid growth because of its purity. However, these experiments proved

that the most significant factor to growing crystals/rock candy was the heat. The heat

was an important factor because it caused the crystals to grow faster because of the

energy produced by the heat. For the sugar crystals/rock candy to grow, atoms that

make up the sugar must chemically bond with atoms of sugar crystals that are growing

on the seeded stick. The heat caused this bonding process to occur faster because of

the increased energy. This energy caused the molecules of sugar to attach faster to

the seeded stick which in turn caused the crystals/rock candy to grow faster. The heat

also helped the solution reach equilibrium faster. In other words, the heat caused the

water to evaporate more quickly so sugar molecules came out of the solution and

moved onto the seeded stick and the water and sugar in the solution became equal.

The seeded stick was important to the growth of crystals because when a non-seeded

string was used in the experiment to try to grow crystals, no growth occurred. The

atoms didn’t have anything upon which to stick and grow. One interesting result that

occurred in the experiment was that when blue dye was introduced, the growth of the

crystals/rock candy was significantly slowed. As shown in Figure 6, at day 6, the table

sugar- water solution with no dye had grown crystals that weighed 22.8 g and the table

sugar-water solution with blue dye had only grown crystals that weighed 12.7 g under

the heated lamp. The slow growth most likely occurred because the chemical reaction

between the blue dye and sugar water that caused the atoms not to bond as quickly.

The final experiment tested the effect of water temperature on the saturation of a

solution. As shown in Figure 7, heated water allowed more sugar to be dissolved than

lower temperature water. At 45.o C, 275 mL of sugar could be dissolved before the

solution became supersaturated. When the temperature was lowered to 4.7 o C, 205

mL of sugar could be dissolved before the solution became supersaturated. More sugar

dissolved when placed in heated water because molecules of water moved faster and

dissolved more sugar. Consistent with the experiment to grow crystals/rock candy the

heating of the initial sugar- water solution was critical. The warmer the water, the more

sugar that would dissolve before the solution became saturated. When the solution was

cooled, it became supersaturated because the sugar solution had more sugar in it than

could stay in its liquid form, and crystals began to grow as the sugar in the solution had

to take on a solid form until equilibrium between the water and sugar was reached. As

was seen in both the growing of the crystals and the testing of the saturation levels,

heat was important to allowing sugar molecules to bond faster to create the

crystals/rock candy and allowing more sugar to be dissolved.

CONCLUSION

In this experiment, it was determined that crystals grown from a pure sucrose- water

solution under a heated lamp grew larger and faster reaching a weight of 42 g than the

table sugar- water solutions grown under the same conditions which reached a weight

of 41 g or the solutions grown at room temperature which reached a weight of 24.6 g or

in the refrigerator which reached a weight of 8.5 g. This result was consistent with the

hypothesis which stated that pure sucrose would produce the largest crystals under a

heated lamp due to the purity of the sugar and the fact that heat would cause the

solution to reach equilibrium faster. If this experiment was conducted again, it was

suggested that the room temperature environment be carefully monitored. This was

suggested so that there are not great temperature variations when the sun goes down

that could impact growth. An additional experiment that could have been conducted

would have been to place the pure sucrose- water solution in an area of room

temperature rather than just under heat to see what the effect of pure sucrose was on

the growth of the crystals. Another experiment that could have been conducted would

have been to seal the top of the container to determine how much air affected the

growth of the crystals.

CITATIONS

Brown, Theodore L., H. Eugene LeMay, Jr. and Bruce E. Bursten. Chemistry: The Central Science. Englewood Cliffs: Prentice Hall. 1994. Print.

"solution." Compton's by Britannica. Encyclopedia Britannica Online School Edition.

Encyclopedia Britannica, 2010. Web. 21 Jan. 2010

<http://school.eb.com/all/comptons/article-9277136>

Wikipedia contributors. "Supersaturation." Wikipedia, The Free Encyclopedia.

Wikipedia, The Free Encyclopedia, 6 Feb. 2010. Web. 17 Feb. 2010.