Analyze Stable Isotopes

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# Analyze Stable Isotopes - PowerPoint PPT Presentation

Climatologists have many strategies for developing an understanding of patterns of climate change . Analyze Stable Isotopes. Many students are familiar with the use of unstable isotopes to “go back in time”. http://www.physlink.com/Education/askExperts/ae403.cfm.

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## Analyze Stable Isotopes

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Presentation Transcript
Climatologists have many strategies

for developing an understanding

of patterns of climate change.

Analyze Stable Isotopes
Many students are familiar with the use of unstable isotopes to “go back in time”.

This worksheet activity guides students toward a very basic understanding of how a study of stable isotopes found in the ice of the Polar Regions can be used to study Earth’s climate history.

Students begin by indicating the number of protons and neutrons in nuclei of a stable isotopes.

a. Express the different in atomic mass units.

2.0141 amu − 1.0078 amu = 1.0063 amu

b. Express the difference as a percentage and express the percent difference in words.

(1.0063 amu ÷ 1.0078 amu) x 100 = 99.85%

This means that H-2 isotopes are 99.85% more massive than H-1 isotopes.

Students then compare the masses of two stable isotopes of an element. For example:
Question 5: What is the average atomic mass of hydrogen atoms in a sample of stable isotopes of hydrogen?

(1.0078 amu x 0.999885) = 1.0076841 amu

+ (2.0141 amu x 0.000115) = 0.0002316 amu

1.0079157 amu

Question 6: How does your answer to Question 5 compare with the average atomic mass of hydrogen on a Periodic Table of the Elements?

Many Periodic Tables of Elements indicate that the atomic mass of Hydrogen is 1.00794 amu. The average mass of stable isotopes was slightly smaller.

Hydrogen-3 is an unstable isotope with a half life of 4500 days. Its presence in a hydrogen sample will increase the average atomic mass of hydrogen atoms.

Students compare the average atomic mass they have calculated with a value on a Periodic Table of the Elements
Question 7: What combination of stable isotopes in water molecules could result in water vapor having a greater tendency to form precipitation as it is transported toward a Polar Regions? Provide a rationale for your answer.

A combination of Hydrogen-2 and Oxygen-18 atoms would result in a water molecule that would be much more likely to form precipitation. As the temperature of water vapor decreases, more massive water molecules would decrease their speed more rapidly and form cloud droplets on condensation nuclei.

Students are posed questions about the precipitation of water vapor as it is transported toward the Polar regions.

The web site below can be used to help students visualize the relationships among the temperature, kinetic energy, and velocity of particles.It can also be used to illustrate the relationships among temperature, kinetic energy, mass, and velocity of particles.

http://www.classzone.com/books/ml_science_share/vis_sim/mem05_pg101_kintheory/mem05_pg101_kintheory.html

Solving the kinetic energy equation for velocity also reveals the affect of mass on the velocity of objects.
Students are asked to explain how water molecules in different layers of ice in the Polar Regions may have different isotopic ratios

Question 10: Why would fewer water molecules containing the more massive isotopes reach the Polar Regions during winter months or during an Ice Age?

Water molecules containing one ore more massive isotope of hydrogen and/or oxygen would have had a greater probability of forming precipitation at lower Latitudes as the water vapor is transported toward the Polar Regions.

Drilling deep into an ice sheet

http://researchnews.osu.edu/archive/lonthmppics.htm

Removing an ice core

http://researchnews.osu.edu/archive/lonthmppics.htm