+0

# Chem help

0
48
3

A geologist discovers a rock containing 12.5% of its original lead-202. He knows the half-life of lead-202 is 52,500 years.How old is the rock?

off-topic
Mar 26, 2020

#1
0

One formula that you can use is:  A(t)  =  A0·(½)( t / t1/2 )

where  t  =  time                                                       =  unknown

A(t)  =  the amount remaining after time t         =  0.125

A0  =  the initial amount                                   =  1.000

t1/2  =  the half-life                                            =  52 500

A(t)  =  A0·(½)( t / t1/2 )          --->     0.125  =  1.000 · (½)( t / 52 500 )

--->      0.125  =  (½)( t / 52 500 )

--->     log(0.125)  =  log( (½)( t / 52 500 ) )

--->     log(0.125)  =  ( t / 52 500 ) · log( 1/2 )

--->      log(0.125) / log(1/2)  =  t / 52 50

--->     [ log(0.125) / log(1/2) ] · 52 500  =  t

Mar 26, 2020
#2
-1

Nice, Geno!

CalTheGreat  Mar 26, 2020
#3
0

0.125 =(1/2)^(t/52500), solve for t

t =157,500 years

Mar 26, 2020