# Homework 9.3.19

APES Homework: elements, half lives and pH

starting at 26 minutes, about the origin of elements, and the "bomb pulse"

If you are off campus, this address will work:

As an investigating scientist at Fukushima Japan, you are tasked with evaluating the decay of radioactive Cesium after the accident.

Problems part I: Due Thursday 9.5.19

1. look up the half life of Cesium 137
2. If the initial percentage of Cesium 137 at the Fukushima Daiichi nuclear power plant accident is 100%, how much will be left after 60 years?
3. graph the decay of Cs 137 on paper, through 6 half lives, labeling your diagram
4. how much of the initial 100% will be found after 70 years?
5. take a photo of your most beautiful graph and data table, and email it to me as part of this assignment.

We can use a simple formula to determine amount left in a half-life scenario like yours. (see your lab sheet as well)

The formula is

At = A0 (0.5)^t

Where

At is the amount at some time t

A0 is the initial amount

t is the number of half lives

This works for uneven numbers of half lives as well.

Example: to find the amount in the above example left after 45 years, divide 45 by the half life in years. Use this number as t.

On your calculator, you might use the y^x keys, or similar keys on your computer.

Verify the answer for 45 years by plotting a dot on your graph above.

Problems Part II: Due Thursday 9.5.19

1. Strontium 90 was found in dairy products in New Zealand after the French tested nuclear bombs on islands near Tahiti in 1960, which they claimed. How much of the original amount would be left in the dairy products today?
2. Chernobyl in the Ukraine exploded in 1986, releasing among other things loads of Cesium 137. How much of the original amount is there today?
3. You find an archaeological bone sample that has 1/64 of the original amount of Carbon 14 present. How many half lives is this?
4. If the half life of Carbon 14 is 5730 years, how old is the bone?
5. The pH of a sample is 1. Is this an acid or a base?
6. The Hydrogen concentration of a second sample is 1 ee -4. What is the pH for this?
7. is this sample more or less acidic than the first?
8. Why are fats more efficient at storing energy than sugars or starches? What other benefits do they offer?
9. Why does crude oil have sulfur in it?
10. Look up Plutonium (the core of a bomb we dropped on Nagasaki), and explain why the dust is so toxic.
11. An element has a half-life of 30 days. If the original sample is 100 grams, how many grams will remain after 30 days?
12. How many will remain after 90 days?
13. How many will remain after 45 days?
14. Using your lab notes, what is the k (decay) value for this? (assume t is in days as well)
15. Another element has a half life of 300 days. What would be the k for this?
16. What is the connection between k value and decay rate?
17. Which is more acidic: NaOH or HCl? Why?
18. How much more acidic is something with a pH 4 than one of pH 5?
19. Which has a higher Hydrogen ion concentration [H+]?
20. How about pH 4 vs. pH 8?
21. What is the pOH of something with a pH of 4?
22. You are told a solution has a Hydrogen ion concentration of 1 ee -12. What is the pH and pOH for this solution?