The half-life of 9142Mo is 15.5 minutes. If you start with 3.5 x 1022 atoms of 9142Mo, how many atoms will remain after 31 minutes?


The half-life of 31H is 12.26 years. If you start with 2.0 x 1015 atoms of 31H, how many atoms will remain after 36.78 years?


The half-life of 6932Ge is 30 hours. If you start with 3.0 X 105 atoms of 6932Ge, how many atoms will remain after 120 hours?


The half-life of 146C is 5730 years. If you start with 2.5 X 109 atoms of 146C, how many atoms will remain after 28,650 years?


The half-life of 198O is 29.1 seconds. If you start with 1.5 x 1022 atoms of 198O, how many atoms will remain after 4 minutes and 51 seconds?

Just use the equation that you have probably been given:

N(t) = N_0e^{-\lambda t}

Where:

\lambda = \frac{ln(2)}{t_{1/2}}

number 1 :

n =3.5 ee 22 * e^- (31/15.5)

n = 3.5 ee 22 * 2.718281828459^ - ( 31/15.5)

n = 3.5 ee 22 * 2.718281828459^-2

n = 3.5 ee22 * 1.3533528323661269189399949497248e-1

n = 4.7363491328144* 10^21 atoms left

Number 2:


n = 2.0 *10^15* e ^ - (36.78 / 12.26)

n = 2.0 *10^ 15 * 2.718281828459^ - 3

n = 2.0 *10^15 * 0.049787068368

n = 9.957413673573e+13 Atoms of H3 atom


Number 3 :

n = 3.0 *10^5 *e^-(120/30)

n = 3.0* 10 ^5 * 2.718281828459^ -4

n = 3.0 *10^5 * 0.018315638889

n = 5494.691666620254 germanium 69


Number 4 :

n = 2.5 * 10^9 e^ -( 28650 / 5730 )

n = 2.5* 10^9 *2.718281828459 ^ - 5

n = 2.5 * 10^9 * 0.006737946999

n= 1.684486749771 e+7 atoms of carbon 14

Number 5 :

n = 1.5 *10^22 * e - ( 291/29.1)

n = 1.5 * 10^22 * 2.718281828459^ - (10)

n = 1.5 * 10^22 * 4.539992976249 e-5

n = 6.809989464373 e+17 atoms of oxygen 19

number 1 :

n =3.5 ee 22 * e^- (31/15.5)

n = 3.5 ee 22 * 2.718281828459^ - ( 31/15.5)

n = 3.5 ee 22 * 2.718281828459^-2

n = 3.5 ee22 * 1.3533528323661269189399949497248e-1

n = 4.7363491328144* 10^21 atoms left

WRONG. You didn't use ln(2)

The actual answer is 8.75 x 10^21


Number 2:


n = 2.0 *10^15* e ^ - (36.78 / 12.26)

n = 2.0 *10^ 15 * 2.718281828459^ - 3

n = 2.0 *10^15 * 0.049787068368

n = 9.957413673573e+13 Atoms of H3 atom

Wrong again...

Ans: 2.5 x 10^14



Number 3 :

n = 3.0 *10^5 *e^-(120/30)

n = 3.0* 10 ^5 * 2.718281828459^ -4

n = 3.0 *10^5 * 0.018315638889

n = 5494.691666620254 germanium 69

Wrong...


Ans: 1.875 x 10^4 = 1.88 x 10^4



Number 4 :

n = 2.5 * 10^9 e^ -( 28650 / 5730 )

n = 2.5* 10^9 *2.718281828459 ^ - 5

n = 2.5 * 10^9 * 0.006737946999

n= 1.684486749771 e+7 atoms of carbon 14

Wrong...

Ans: 7.8125 x 10^ 7 = 7.81 x 10^7


Number 5 :

n = 1.5 *10^22 * e - ( 291/29.1)

n = 1.5 * 10^22 * 2.718281828459^ - (10)

n = 1.5 * 10^22 * 4.539992976249 e-5

n = 6.809989464373 e+17 atoms of oxygen 19

Wrong...

Ans: 4.935 x 10^19 = 4.94 x 10^19

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