What is the half-life of 20 g of a radioactive sample if 5 g remain after 8 minutes?

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Answer 1 · 2016-05-31T09:23:09

$4 min.$

$m_i=m_rxx2^n$

$m_i=" is the initial mass"$

$m_r=" is the remaining mass after n periods"$

$n " is the number of periods "$

$2^n=m_i/m_r$

$2^n=20/5$

$2^n=4$

$2^n=2^2 " "=> n=2$

$n=(time)/("half-life")$

$"half-life "= (time)/n$

$"half-life" =( 8 min)/2 = 4 min$

$20 \ g -> 10 \ g -> 5 \ g$