Question

P 101uu sus
The half - life period of radioisotope is 20 seconds. Starting with 0.2g of the isotope, the amount left alte
2 miniutes is
[ ]
h) 0312 mg
c) $.0031259
d) 0.525 mg​

Answer 1

Answer:

0.003125 g

Explanation:

At initial = 0.2g

After every 20 secs its halved

2 minutes = 120 secs = 20*6 secs

=> 6 half time

After 2 minutes = 0.2g/(2)⁶ = 0.2/64 g

= 0.003125 g

=

Answer 2

Hello!

The half - life period of radioisotope is 20 seconds. Starting with 0.2 g of the isotope, the amount left after 2 minutes is?

• We have the following data:

The half-life is the time of half-disintegration, it is the time in which half of the atoms of an isotope disintegrate.

P (Half-life) = 20 sec

mo (initial mass) = 0.2 g

T (Elapsed time for sample reduction) = 2 minutes = 120 sec

x (number of periods elapsed) = ?

m (final mass after time T) = ? (in grams)

• Let's find the number of periods elapsed, in formula the half-life (P) of the radioactive sample, let's see:

$T = x*P$

$120 = x*20$

$20\:x =120$

$x = \dfrac{120}{20}$

$\boxed{x = 6}$

• Now, Let's find the final mass after time T, let us see:

$m = \dfrac{m_o}{2^x}$

$2^x = \dfrac{m_o}{m}$

$2^6 = \dfrac{0.2}{m}$

$64 = \dfrac{0.2}{m}$

$64\:m = 0.2$

$m = \dfrac{0.2}{64}$

$m = 3.125*10^{-3}$

$\boxed{\boxed{m = 0.003125\:g}}\:\:\:\:\:\:\bf\green{\checkmark}$

Answer:

c) 0.003125 g

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