B radioactivity the readioactivity of an element can

B. Radioactivity
The readioactivity of an element can be described by the following equation:
N
t
= N
o
e
kt
(1)
where N
t
represents the radioactivity at some time, t. N
o
represents the initial
radioactivity, and k is the radioactivity constant. If you take the ln of both sides of
equation(1), we get:
lnN
t
= lnN
o
- kt (2)
Notice that Equation 2 is a linear equation of the form y = mx + b ( also called slope
intercept form ). Let us express Equation 2 above as follows:
lnN
t
= - kt + lnN
o
y = mx + b
Now we can see that the y-intercept b is equal to lnN
o
. We can also equate m with -k,
which tells us that the slope is negative.
Once the value of the radioactivity decay constant k is known, the radioactivity at any
other time (t) can be calculated from the Equation (1).
Using the following data for a sample of Uranium-235, plot the natural log ( ln ) as a
function of time.
Table: Radioactivity Experimental Data
Time (10 9 Years)
Average Radioactivity
(Counts per minute)
ln(Average Radioactivity)
0.00 1000
0.15 860
0.30 750
0.45 645
0.60 560
0.75 480
0.90 420
xvi

From the graph determine the slope and y-intercept of the line of ”best fit” line through
the data points.
slope:
ln(radioactivity)
Time(10 9 years )
=
y-intercept: ln(radioactivity) =
What percent of the original sample remain after 1.0 billion (10 9 ) years?
When you are done with this assignment, submit the following to your instructor:
1. The page on Boyl’es Law and the accompanying graph
2. The page on radioactivity decay and the the accompanying graph
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xix

Formula Writing
Name:
Given the ions shown, fill in the Table with the appropriate chemical formula.
Anion →
Cl
- 1
SO
- 2
4
CO
- 2
3
NO
- 1
3
Cation ↓
NH
+
4
Ag
+
Cu
2+
Ca
2+
K
+
Hg
2+
Fe
3+
Zn
2+
Al
3+
Mg
2+
Cr
3+
xx

Write the name of each ion under the ion formula. Then, using the ion names, fill in the
Table with the name of the compound formed from each ion pair.
Anion →
Cl
- 1
SO
- 2
4
CO
- 2
3
NO
- 1
3
Cation ↓
NH
+
4
Ag
+
Cu
2+
Ca
2+
K
+
Hg
2+
Fe
3+
Zn
2+
Al
3+
Mg
2+
Cr
3+
xxi

Name:
Fill in the blank in the Table below. Fill in the third and fourth column with the chemical
formula and name, respectively, of the barium salt that contains the anion in the acid
formula.
Formula of
Acid
Name of Acid Formula of
Barium Salt
Name of Barium Salt
Sulfuric Acid
Chloric Acid
Hydrobromic Acid
Nitric Acid
Phosphoric Acid
Carbonic Acid
Fill in the blank in the Table below.
Formula of
Acid
Name of Acid Formula of
Aluminum
Salt
Name of Aluminum
Salt
Aluminum Nitrate
Aluminum Sulfate
Aluminum Hypochlorite
Aluminum Phosphate
Aluminum Chlorate
Aluminum Nitride
xxii

Equation Writing
Name:
For each of the following write a balanced chemical equation. An upward pointing arrow
( ↑ ) refers to gas formation. A downward pointing arrow ( ↓ ) refers to formation of
precipitate. The triangle ( 4 ) for decomposition reactions indicates that heat must be
added for the reaction to occur.