Asample originally contained 1.28 g of a radioisotope. it now contains 1.12 g of its daughter isotope. how many half-lives have passed since the sample originally formed?

3 half lives

Solution :

Formula used :

where,

a = amount of reactant left after n-half lives = initial amount - amount of daughter isotope= (1.28-1.12)= 0.16 g

= Initial amount of the reactant = 1.28 g

n = number of half lives = ?

Putting values in above equation, we get:

Therefore,  3 half-lives have passed since the sample originally formed.

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