Effect of Surface Area on Reaction Rate

Surface Area vs. Reaction Rate

How does the surface area of pure cane sugar cubes affect the rate of dissolution in water?

Chandler Hultine

Abstract

The purpose of this lab was to investigate how surface area affects the reaction rate of a substance in a solution. This lab was put together to find out how differentiating surface areas of pure cane sugar cubes would affect the rate of dissolution in water.

The investigation was undertaken by using five different groups of sugar cubes, each group having a different surface area than the others. The cubes were submerged and stirred in a solution of water until they completely dissolved, and the time it that it took them each to dissolve was recorded. The longer the time it took for the cubes to dissolve, the slower the reaction rate, and vice versa.

The initial hypothesis, if the surface area of the cube increases, then the reaction rate of the dissolution of the cube in water will also increase because more of the cube will be exposed to the water which will allow for more collisions of particles to occur at a time, was accepted due to a positive correlation between dissolution times and surface area of cubes. The more broken up a cube was, the faster it tended to dissolve in water and vice versa, because the more broken up cubes had more surface area. (Abstract Words: 212)

Introduction

The overall aim of this lab is to investigate how surface area is related to reaction rate in terms of the dissolution rate of a substance in a solution. This lab will be experimenting with sugar cubes of the same volume, but different surface areas to see how exactly surface area affects the rate of dissolution.

How does the surface area of pure cane sugar cubes affect the rate of dissolution in water? If the surface area of the cube increases, then the reaction rate of the dissolution of the cube in water will also increase because more of the cube will be exposed to the water which will allow for more collisions of particles to occur at a time.^3,6

With most things in life, size is a very important factor that people consider in many choices they make, whether it be deciding between the newest smartphones or burning wood chips versus entire logs in a fire.¹ Seeing how size affects something is key when taking an item/idea and making it more effective. The purpose of this experiment is to see how the amount of surface area of a substance is related to the reaction rate when said substance is placed into a solution.⁵ This investigation is to see how the reaction rate of a substance can be either increased or decreased when placed into a solution.

Investigation

For the investigation, a variety of sources that related to how surface and dissolution/reaction rates are related. The [main] sources include but are not limited to:

• Research on the topic done by NASA,
• An excerpt from Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems,
• And experiment research from sciencebuddies.org titled Big Pieces or Small Pieces: Which React Faster?.

These sources have provided a great amount of background information, especially the article by NASA involving an explanation on the correlation between surface areas and reaction rates.

Materials

In order to complete this experiment, the following materials were required:

• 25 Sugar cubes (any brand, just make sure all the same)
• 1 Timer
• 5 Beakers (250mL)
• 1 Pipet
• 1 Thermometer
• 1 Knife
• 1 Paper towel or piece of paper (cut sugar cubes on)
• 1 Hammer or weighted object (to crush one of the sugar cubes into a powder like state)
• 1 Pencil and paper (to record observations)
• 1 Stirring device of any kind (like a chopstick)

Constants

Water source, brand of beakers, size of beakers, amount of water, stirring device, type of sugar cube, temperature of water, temperature of surroundings, temperature of beakers, cuts in sugar cubes, pipets, timer, thermometer

Procedure

1. Divide the 25 sugar cubes into groups of five so that each group has five sugar cubes.
2. Leave the first group untouched. This will be the group that has the smallest surface area.
3. Take the second group of five sugar cubes and, using the knife, cut each cube in half.
4. Take the third group of sugar cubes and cut each cube into quarters (cut each one in half then cut the halves in half).
5. The fourth group will be cut into eighths.
6. The last group of sugar cubes will be completely ground up into a powder. This will be the group with the greatest surface area.
7. Once all the cubes are cut up and put into groups, fill up each of the 5 beakers with water to the 200mL mark. Use a pipet to make the measurement precise.
8. Wait 30 minutes after filling the beakers with water to ensure they are all room temperature.
9. Begin with the uncut sugar cube. With the timer and stirring device at hand, place the uncut cube into the water-filled beaker and begin the timer and stirring as soon as the sugar cube is placed in the water.
10. Stir the sugar cube in the water until it completely dissolves/disappears in the water.
11. Stop the timer as soon as the sugar cube completely dissolves.
12. Record the results on a pre-made data table.
13. Repeat steps 6 to 9 for all variants of the sugar cube for one group.
14. Repeat the entire experiment for all 5 groups of sugar cubes, making sure that one group is finished before moving onto another group. DO NOT finish dissolving all of the sugar cubes of one specific surface area size and then moving onto another set of the same surface area sized cubes; make sure the experiment is carried out group by group. Treat each group with the five different surface area sized sugar cubes as an individual experiment. This way a total of 5 experiments will be carried out.

Data

Trial 1

Trial 2

Trial 3

Trial 4

Trial 5

Mean time for full sugar cube: 423.4

Mean time for half sugar cube: 223.4

Mean time for quarter sugar cube: 129.2

Mean time for eighth sugar cube: 75.8

Mean time for powder sugar cube: 52.6

Results and Discussion

The results of this experiment show that a more broken up sugar cube resulted in a faster dissolution rate of the cube in water, and vice versa when there were longer rates of dissolution for sugar cubes that were less broken up. Since the purpose of this experiment was to find the relationship between surface area and reaction rate, this experiment was successful.

Trial 1 data shows the times nearly being cut in half as the sugar cube becomes more crushed up, except for the transition between the powder and sugar cube broken up into eighths.

Trial 2 data also shows the time between each tier of sugar cubes being split in half as the surface area increases. However, this is not true for the half-broken up and quarter-broken up sugar cubes. The time in seconds for dissolution rate for those two sugar cubes only had a difference of ~50 seconds, which is not even close to half. This makes me wonder what happened during that part of the lab, because the data does not follow the conventional trend like the rest of my experiment results. A possible source of error for this trial was that I did not collect all of the sugar from the sugar cube after it was cut. When all of the sugar is not completely collected, the data can become skewed because not all of the sugar cube is actually being dissolved in the solution.

Trials 3, 4, and 5 all show around the similar results. The times are very close to each other for each size sugar cube that was dissolved. Trials 3, 4, and 5 are also relatively close to the data shown in trial 1. This shows that there was a little less precision that went into trial 2.

What does all of this data mean? Well for starters, the data and experiment are relevant for any other experiment out there that tries to determine the relation between surface area and reaction rate. The reason for this is because whenever different rates of reaction are being tested for, a change in the surface area of a reactant/variable will have an effect on the rate of reaction, because the alteration of surface area means that the frequency of particle collisions is altered as well.^1,3,7 For example, if the surface area (of an object that is about to be placed in a solution) is doubled, that means there will be twice as much area for particles to potentially interact with on the object as compared to the original object that has the original surface area.³ This is true for all aspects of reaction rate; surface area plays a substantial role whenever reaction rate is tested for.^1,3

Conclusion

Initial Hypothesis: If the surface area of the cube increases, then the reaction rate of the dissolution of the cube in water will also increase because more of the cube will be exposed to the water which will allow for more reaction between water and sugar cube to occur at one time.^3,6

There was a strong, positive correlation between the data that was collected and the initial hypothesis. From looking at the data, it is apparent that the cubes that were more broken up that had more surface area dissolved much faster than a cube that was less broken up and did not have as much surface area. The data shows that more surface area does mean faster reaction rate, and vice versa.³ The powder/completely crushed up sugar cube had the quickest time for dissolution in water which was on average 52.6 seconds, whereas the full sugar cube that was untouched and had the smallest amount of surface area had the slowest time for dissolution which was on average 423.4 seconds. Therefore, the hypothesis is accepted with the support of the data. The larger cubes that were not cut up took the longest to completely dissolve, whereas the finely crushed up cubes dissolved quickest.⁵

The accuracy of this experiment could be slightly improved in the future by adapting a more consistent and reliable method of stirring the sugar cubes around when they are placed in water. This would improve the accuracy of the time that each cube takes to completely dissolve in the solution of water.

Bibliography

Reaction Rates. Publication. NASA, n.d. Web. ¹

Allen, Loyd V., Nicholas G. Popovich, Howard C. Ansel, and Howard C. Ansel.Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems. Philadelphia: Lippincott Williams & Wilkins, 2005. Print. ²

Clark, Jim. “The Effect of Surface Area on Rates of Reaction.”The Effect of Surface Area on Rates of Reaction. N.p., n.d. Web. 06 May 2013. ³

Bayer HealthCare, 2005. “Temperature and Rate of Reaction,” Bayer HealthCare, LLC [accessed May 8, 2007]http://www.alka-seltzer.com/as/experiment/student_experiment1.htm. ⁴

Olson, Andrew. “Big Pieces or Small Pieces: Which React Faster?”Big Pieces or Small Pieces: Which React Faster?Science Buddies, n.d. Web. 06 May 2013. ⁵

Kenneth Connors, Chemical Kinetics, 1990, VCH Publishers, pg. 14 ⁶

Isaacs, N.S., “Physical Organic Chemistry, 2nd edition, Section 2.8.3, Adison Wesley Longman, Harlow UK, 1995. ⁷

(Bibliography Words: 126)