Untitled - Kelly Walsh High School

Nuclear Chemistry 301
t 1/2 (ln 2)/k (ln 2)/6.33 10 3 min 1 0.693/6.33 10 3 min 1
109.47867 109 min
A sample of iron-55 weighs 3.75 mg. The decay constant for this isotope is
0.26 y 1 . How much iron-55 will remain in the sample after 6.0 years?
We can recopy and label the variables to get:
N 0 3.75 mg Nt ? k 0.26 y 1 t 6.0 y
The only equation containing these four variables is: ln (N t/N 0) kt
We can enter the values into the equation to get:
ln (0.26 y1 ?
a
) (6.0 y) 1.56 (unrounded)
3.75 mg b
e1.56 ?
a
0.210136 (unrounded)
3.75 mg b
? (0.210136) (3.75 mg) 0.78801 0.79 mg
A sample of argon-41 contains 4.25 mg of this isotope after 254 s. The decay constant
for this isotope is 6.33 10 3 min 1 . What mass of argon-41 was originally
in the sample?
We can recopy and label the variables to get:
N 0 ? N t 4.25 mg k 6.33 10 3 min 1 t 254 s
The only equation containing these four variables is: ln (N t/N 0) kt
We can enter the values into the equation to get:
ln (6.33 103 min1 4.25 mg
a b
) (254 s)
?
The time units do not match; therefore, we need to add a conversion step.
ln (6.33 103 min1 ) (254 s)
0.026797 (unrounded)
e0.026797 1 min
a
60s
4.25 mg
a b
0.97355885 (unrounded)
?
? (4.25 mg)/(0.97355885) 4.3654269 4.37 mg
b
mg
a4.25 b
?