The Effects of Acids on Seashell Corrosion

Carla GiannandreaAcademy of Notre Dame de Namur

Question

What will happen to the percent change in the mass of seashells when soaked in different acid solutions?

Background Information

• Earth’s oceans absorb the carbon dioxide in the air emitted by humans.

• The acidity level of water has risen from 8.2 to 8.1

• Acids are considered either strong or weak• There are three types of acids, monoprotic,

diprotic, and tripotic acids.• Seashells are comprised of three shell layers...

• Proteinaceous periosteum• Prismatic layer• Inner pearly layer of nacre

Hypothesis

The percent change of the mass of seashells will increase as the pH levels of the different acid solutions decrease

Materials

• 72 seashells• Balance• 36 large glass jars• pH meter• HCl (Hydrochloric Acid)

• H2SO4 (Sulfuric Acid)

• HNO3 (Nitric Acid)

• Distilled water

http://sciencetools-w310.wikispaces.com/file/view/1w310_005.JPG/125401779/1w310_005.JPG

Procedure

• Three different solutions of 500 mLs of HCl were made, each with different pH level

• Each solution was then put into a different jar.

• Steps one and two were done with acids HNO3 and H2SO4 as well.

• Distilled Water was put into nine different jars.• The seashells were massed and put into the

solutions for seven days.• When taken out, they were massed again and the

percent change in mass was found in each seashell.

• Independent Variables• Different types of acids• Different pH levels of acids

• Dependent Variables• Percent change in the mass of the seashells

• Control• Seashells soaked only in distilled water

• Constants• Approximately same sized seashells• Same amount of solution in each jar• Soaked for the same amount of time• Maintained under tha same conditions

Average Percent Decrease in Mass of Seashells Soaked in HCl Solution

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Distilled Water HCl ph 5 HCl ph 4 HCl ph 3

Avg. Percent Change in Mass

Average Percent Decrease in Mass of Seashells Soaked in HNO3 Solution

0

0.1

0.2

0.3

0.4

0.5

0.6

Distilled Water HNO3 ph 5 HNO3 ph 4 HNO3 ph 3

Average Percent Change in Mass

Average Percent Decrease in Mass of Seashells in H2SO4 Solution

0

0.1

0.2

0.3

0.4

0.5

0.6

Distilled Water H2SO4 ph 5 H2SO4 ph 4 H2SO4 ph 3

Average Percent Change in Mass

T-Test P. Value

Distilled Water to HCl ph 5 0.043

Distilled Water to HCl ph 4 0.043

Distilled Water to HCl ph 30.681

Distilled Water to HNO3 ph 5 0.168

Distilled Water to HNO3 ph 4 0.765

Distilled Water to HNO3 ph 3 0.938

Distilled Water to H2SO4 ph 5 0.745

Distilled Water to H2SO4 ph 4 0.978

Distilled Water to H2SO4 ph 3 0.191

Discussion and Analysis

Conclusion• The results of this experiments

concluded that short term exposure to acid solutions does not affect the mass of seashells.

• A source of error could have been inaccurate readings of the pH meter when making the solutions.

Further Research

• Testing change in softness of the seashells instead of change in mass

• Using different types of seashells• Using a control with pH 8.1 (the pH

level of the ocean)• Using a control of salt water

instead of distilled water

ReferencesAcid. (1990). In S. P. Elliot, M. Goldstein, & M. Upshall (Eds.), Webster’s New World Encyclopedia (9th

ed., p. 7). United States of America: Prentice Hall. (Original work published 1948)

Acid and Base Chemistry. (n.d.). Retrieved October 6, 2002, from Shoder website: http://www.shodor.org/unchem/basic/lab/

Acids. (n.d.). Retrieved October 6, 2010, from http://hyperphysics.phy-astr.gsu.edu/hbasic/chemical/acid.html

Bivalve Shell. (n.d.). Retrieved from http://en.wikipedia.org//_shell

Brewer, P. G., & Barry, J. (2008, October 7). Rising Acidity in the Ocean: The Other CO2 Problem. Scientific American. Retrieved from http://www.scientificamerican.com/.cfm?id=rising-acidity-in-the-ocean&page=2

Carpi, A. (n.d.). Acids and Bases. Retrieved 2003, from http://www.visionlearning.com/library/module_viewer.php?mid=58

Chemistry (A. C. Wilbraham, D. D. Staley, M. S. Matta, & E. L. Waterman, Trans., pp. 271,589-591, 600-607). (2008). Boston, Massachusetts: Pearson Prentice Hall.

References (continued)Hardt, M. J., & Safina, C. (2010, August). Threatening Ocean Life from the Inside Out. Scientific

American, 66-73.

Horne, F. (2006, October 23). How are seashells created? Or any other shell, such as a snail’s or a turtle’s? [Special section]. Scientific American. Retrieved from http://www.scientificamerican.com/.cfm?id=how-are-seashells-created

pH Indicator. (n.d.). Retrieved from http://en.wikipedia.org//_indicator

Seashells. (n.d.). Retrieved October 4, 2010, from Wikipedia website: http://en.wikipedia.org/wiki/Seashell

Where do Seashells come from? (n.d.). Retrieved from http://www.seashellsandsuch.com/articles/wherecomefrom.php